1998 Series 60 Poor Fuel Economy [Archive] - TheDieselGarage.com

: 1998 Series 60 Poor Fuel Economy


love0126
04-02-2011, 05:43 AM
Hi all,

I have a 98' FL Century running at 1.1 M on the original rebuild. I did a head gasket at about 800 K, and put in 3 injectors at about the same time. The thing runs like a swiss watch. The problem is that it's getting very poor fuel economy. It has been getting about 4 MPG over the past month. Before that, it was with a different owner, so I don't know what it was doing. I replaced the oil pan gasket and checked the cylinders for wear, and they were very smooth. Any ideas what I should look into? Old DDEC III isn't throwing any codes. Fuel is clean, and so are the air and fuel filters. The trailer doesn't even have any smoke stain on it whatsoever. She's burning clean.

love0126
04-02-2011, 07:22 AM
Haha I feel retarded. I forgot to calculate deadhead and bobtail miles. True fuel economy is 5.0 MPG. My business partner ran this exact 500 HP Detroit 60 and averaged 6.7 MPG over the road. Still, 5.0 is not acceptable even with the fuel surcharge. I've thought of the following to do: Check clutch for slippage, add a gallon of Lucas oil treatment, add a good quality fuel treatment to clean the combustion chambers, and finally, have a shop scan the DDEC III to make sure there aren't any codes that aren't setting the Check Engine Light. Anything else? I know it's tougher to do a compression test on these trucks and to verify nothing is wrong internally.

wcdiesel
04-02-2011, 09:56 AM
Check your fuel pressure after the secondary filter - 15 psi at idle -65 to 70 psi at 1800 plus , check your overhead adjustments

dzljon
04-02-2011, 03:11 PM
I am thinking it is time for a cam.. 1.1M miles plus idle time on the the origional is very good, i would start by checking lift on the intake and exhaust as well as the injector lobe.

379Longhood
04-02-2011, 04:34 PM
:sprayw
You may also want to check for exhaust restriction and possible late injection timing. After you check valve lift.

love0126
04-02-2011, 11:50 PM
These are all tremendous suggestions. I'm gonna be pulling the cover off and checking the valves when I see it next. It very well could be a cam or injection timing. The truck is not fitted with EGT so I can't monitor that unfortunately. I will also check fuel pressure. Where is the schrader valve on the fuel line to check fuel pressure?

Truck 505
04-03-2011, 12:06 AM
What tranny does it have and what rpm and gear are you running when loaded.

tc2
04-03-2011, 12:06 AM
There is no schrader valve. You remove the fuel temp. sensor from the fuel pump and check the pressure there.

Before you get too crazy checking all that mechanical stuff, get someone to hook a pro-link or laptop with software to it and make sure the sensors are reading properly, particularly the boost pressure sensor.
I've had quite a few of the boost sensors become quite inaccurate without setting a code. If it is inaccurate it could result in low power or excessive fuel consumption.
I usually check the sensor reading key on engine off and make sure it is pretty much zero, then I hook an air to air pressure tester up after the turbo and pressurize the air to air, piping and intake to 20 psi or so , and check that the sensor reads that accurately. You also get an idea if there are any significant boost leaks at the same time.

These are all tremendous suggestions. I'm gonna be pulling the cover off and checking the valves when I see it next. It very well could be a cam or injection timing. The truck is not fitted with EGT so I can't monitor that unfortunately. I will also check fuel pressure. Where is the schrader valve on the fuel line to check fuel pressure?

love0126
04-03-2011, 01:33 AM
It has the Eaton 13 speed. Standard highway gears. If I remember correctly. I was wondering about that boost sensor. Most I've seen fail cause the turbo to not boost. There is absolutely no soot on our trailer whatsoever. I will authorize its driver to take it in to Freightliner. She could also have a very heavy foot. It's wide open.

Truck 505
04-03-2011, 01:40 AM
A detroit does not like to be lugged. It may get better mileage in 12th gear than 13th gear when loaded because the motor will be running about 200 rpm faster.
We have one with a 10spd and it gets better mileage in 9th loaded than in 10th.
It gets its best mileage between 1500-1700 rpm.

love0126
04-03-2011, 05:28 AM
I'm definitely aware that Detroits love their rpm. My co owner deals with this driver much more than I do. He said he is unaware if she has been lugging it or not but that he would verify her driving habits. I would love to throw it on a scanner to see what is coming up that doesn't set the check engine light. I won't be seeing the truck till at least Wednesday. I will be sure to check the valves for proper lash. Does anyone have the lash specifications for the valves handy?

PGM
04-03-2011, 07:56 AM
Think your getting a bit ahead of yourself with all the mechanical stuff, look for the simplest things first.

Detroit are basic and reliable lumps, however they need to be setup right.

Johnp3
04-03-2011, 06:46 PM
The first thing you want to check is the fuel pressure, second and what I would think the problem is, check the CAC, do it at the turbo outlet first, and check the boost sensor, and check the vent for air bypassing the valve guides, test it at 35 lbs. Then block off the CAC and test that at 35 LBS, it should hold pressure for 15 seconds with a maximum 4 lbs loss. If you have access to a data link check the throttle for 100% travel.
Just a thought!

theakerstwo
04-03-2011, 09:11 PM
And while testing the air/air cooler pressure it up against the head also with about 20 or 25 lbs. If pressure dont come up go turn the engine some and you will find at some point there will be intake and exhaust valves closed enough on all cylnders engough to pressure it up. Some times you find intake gaskets leaking big time. I found a craked manifold in one one time and a pipe plug missing in a cat engine one time.

theakerstwo
04-03-2011, 09:17 PM
Also on a DDEC 4 at one point the programs was i tought it was in 98 had the boost sensor read out frozen untill vehicle starts to move.I remenber when it came out cause before you could monitor the boost with the labtop while pressuring the intake.After that the ecm who only show no boost.That was part of the epa penitalty for the manufactors not complying soon enough.

John_G
04-03-2011, 11:40 PM
A S60 cam should last the life of the vehicle, unless it fails the published "re-use guidelines" in the service manual, no matter how bad it *looks* - LEAVE IT!

Is the fan staying one excessively?

How many HOURS are being added each trip?

What's the road speed and load?

A C120 with a 475HP S60, at reasonable speeds of 65 MPH or LESS should be getting 6.5 MPG consistantly if idle time is minimal. Every 1 MPH over 60 will drop MPG 0.1, so if you get 7.0 MPG @ 60, you should expect that at 65 it will be 0.5 MPG less, or 6.5 MPG. If the driver is running the enigne 24x7, your mileage will TANK. Idle time should be below 20% for a "good" driver and below 10% for an excellant one. All the diagnostics and hardware in the world won't fix high idle time, high speed limits or a driver wasting fuel.

Johnp3
04-04-2011, 01:18 AM
In addition to what JohnG said the BS about revving the motor us is just that BS. the max torque is at 1200 RPM, and the sweet spot is at 1550 RPM that is were the torque and HP graphs cross. running at a hill is different but to drive at an elevated RPM just burns fuel.
You might want to ask the shop that did the overhaul if they checked CAM timing after the overhaul, and what was the measurement? It is possible to be out a tooth, and it does change output.
I worked in a freightliner shop and did a lot more cams in CAT's than I ever did in S60's.

love0126
04-04-2011, 06:47 AM
A S60 cam should last the life of the vehicle, unless it fails the published "re-use guidelines" in the service manual, no matter how bad it *looks* - LEAVE IT!

Is the fan staying one excessively?

How many HOURS are being added each trip?

What's the road speed and load?

A C120 with a 475HP S60, at reasonable speeds of 65 MPH or LESS should be getting 6.5 MPG consistantly if idle time is minimal. Every 1 MPH over 60 will drop MPG 0.1, so if you get 7.0 MPG @ 60, you should expect that at 65 it will be 0.5 MPG less, or 6.5 MPG. If the driver is running the enigne 24x7, your mileage will TANK. Idle time should be below 20% for a "good" driver and below 10% for an excellant one. All the diagnostics and hardware in the world won't fix high idle time, high speed limits or a driver wasting fuel.

Honestly I don't know what she's been idling for in terms of time. She has been having a lot of off time on the road, but we recently switched carriers. This guy seems to know how to run a truck. I do know she uses high idle, which is deemed appropriate given the slow idle s60 bearing problems I've read for. I wish we had an APU. I really do. At this point, I intend to get a perspective of her idling / driving characteristics, check crankcase pressure, and see how much reefer fuel she's been using. I'm so dumbfounded that it runs so cleanly and yet is getting crap for fuel economy!!! ARGH!

John_G
04-04-2011, 01:11 PM
A typical big bore diesel will burn 0.65 to 3.0 GPH at idle, the lower end is for "just ideling" and the upper end includes HVAC, household loads and the fan in hot weather at 900 RPM.

If you idle it 10 hours/day total and assume an average burn of 1.5 GPH, that represents 15 gallons per day wasted. Factoring the cost of fuel and you get about $50/day out the stack for nothing. A decent hotel room can be had for less and they serve breakfast!

An APU is about $8k installed, actually the ones I like better are less, so in 400 days you have made your $$$ back just in terms of fuel, reduced maintenance will shorten that some and the engine lasts longer too.

love0126
04-04-2011, 09:12 PM
A typical big bore diesel will burn 0.65 to 3.0 GPH at idle, the lower end is for "just ideling" and the upper end includes HVAC, household loads and the fan in hot weather at 900 RPM.

If you idle it 10 hours/day total and assume an average burn of 1.5 GPH, that represents 15 gallons per day wasted. Factoring the cost of fuel and you get about $50/day out the stack for nothing. A decent hotel room can be had for less and they serve breakfast!

An APU is about $8k installed, actually the ones I like better are less, so in 400 days you have made your $$$ back just in terms of fuel, reduced maintenance will shorten that some and the engine lasts longer too.

I have seen some units in the 6K range. Who makes the best APU's out there? Both in terms of reliability as well as effectiveness at keeping the cab at a good temp?

Johnp3
04-04-2011, 09:29 PM
I have seen some units in the 6K range. Who makes the best APU's out there? Both in terms of reliability as well as effectiveness at keeping the cab at a good temp?

That is a good question on the APU's I would imagine it may be different, for units that run in areas where the extremes of temperature are.
The most in Idle time I have ever seen was 76%, I have seen many that were in the high 60's.

love0126
04-04-2011, 10:11 PM
Yikes that is a lot of idle time. I will start keeping a log of idle hours. I talked with my co owner. He said the driver likes to idle it. She was only doing 1900 to 2k miles per week with the old carrier, so she had a ton of downtime on the road. I bet anything the truck will be closer to 6 MPG than 5 when she runs a bit more. We will be checking the valves when we can get it in the shop. Not too tough to pull the cover off and plug a feeler gauge in there. Also we intend to get an oil analysis done next oil change to check the condition of the bearings. I know some c12's that have never seen 6mpg. lol

undeadmechanic
04-06-2011, 12:10 AM
I'm definitely aware that Detroits love their rpm. My co owner deals with this driver much more than I do. He said he is unaware if she has been lugging it or not but that he would verify her driving habits. I would love to throw it on a scanner to see what is coming up that doesn't set the check engine light. I won't be seeing the truck till at least Wednesday. I will be sure to check the valves for proper lash. Does anyone have the lash specifications for the valves handy?

Intake: 0.008"
Exhaust: 0.026"

Do you have an injector height tool for this engine? If you're checking the valves, might as well check the injector height too. All of this information is on a sticker on the left side of the valve cover *unless* the cover has been replaced or someone got a little too overzealous with a pressure washer.

Also, you might want to record the calibration/trim codes of each injector. Whenever I open one up, I usually find one or more that the injector code and the code in the ECM for that cylinder do not match. Just write them down and you'll have to take it to someone that can check/set injector codes.

Good luck!

love0126
04-06-2011, 12:25 AM
Yes my partner in the business does have the injector tool. I will definitely plan on checking them plus the codes to make sure the DDEC III is programmed correctly. I know the driver is being worked better now. 2k miles in 4 1/2 working days. Deadhead mileage less than 10%. This should increase fuel economy. She was doing a ton of idling before.

love0126
04-13-2011, 10:17 PM
I got to see the truck today. I did a quick check for blowby out the oil filler tube. Just a bit of crankcase blowby comes wafting out the tube. I have been unable to get the tools from my business partner, due to conflicting schedules. Those tools would be the ones for adjusting the injectors. Therefore it is going in to Detroit diesel in Fargo for top adjustment and injection pump check. Also, I notice the truck has a weird dust colored film on the tractor. First it started on just the drivers side. Now it is on both sides. It uses about a gallon to 2 between oil changes and does leak a little oil. I dint check the coolant level. Any ideas about the mystery film?

truckdriver
04-14-2011, 12:17 AM
John G gave the easiest thing to check and I'd bet the problem. Put it on the computer and look at the idle time and average road speed. The main factor in fuel mileage is the DRIVERIf the average speed is more than about 60mph then the driver is likely driving 70-75 and that will kill your mileage. I run about 62mph(1400rpm) and I don't race it from a stop and if my truck gets less than 8mpg I'm pissed. With my driving habits I got 6.5 constantly from my 2000 379x 550 cat. That truck had 3.70 gears with 22.5lopro rubber and 65 was 1550 so taller gears would have greatly improved my mileage. My current truck is a 95 FLD with DDECIV 470.

love0126
04-14-2011, 12:43 AM
John G gave the easiest thing to check and I'd bet the problem. Put it on the computer and look at the idle time and average road speed. The main factor in fuel mileage is the DRIVERIf the average speed is more than about 60mph then the driver is likely driving 70-75 and that will kill your mileage. I run about 62mph(1400rpm) and I don't race it from a stop and if my truck gets less than 8mpg I'm pissed. With my driving habits I got 6.5 constantly from my 2000 379x 550 cat. That truck had 3.70 gears with 22.5lopro rubber and 65 was 1550 so taller gears would have greatly improved my mileage. My current truck is a 95 FLD with DDECIV 470.

elmerfudd
I will have them hook it up and check driving habits. Maybe set the governor to 65. I know she likes to idle, but we went from 6.7 first trip out with the new driver to 5 every other time. It happened very suddenly. We are running 1600 or so @ 70. Seems to run good in 13th. He have 24.5's, standard radius. New rubber too.

love0126
04-15-2011, 11:33 PM
The truck had the overhead done yesterday. The tech didn't raise any issues, so I suspect the tuneup was non-eventful. The driver is hauling some beans out to Ohio @ 80K, so we will get our first fuel economy spot check in Indiana from Fargo (they always have the cheapest fuel out there). The driver says it is running about the same. But it didn't have any drivability issues before. Just the bad fuel economy. It should be getting about 1-1.5 MPG better. The driver will hand me the report tomorrow as she passes through.

magoo68
04-16-2011, 03:14 AM
alot of your fuel mileage may be lost due to winter blend fuels and bad weather within a month you should pick up some mileage once they burn up the leftover blends

love0126
04-16-2011, 03:23 AM
alot of your fuel mileage may be lost due to winter blend fuels and bad weather within a month you should pick up some mileage once they burn up the leftover blends

Wouldn't that be a miracle if it was just the fuel? At these prices, it's cutting into our maintenance budget big time. I can't wait for the first fuel spot check to come back. Has anyone ever tried any aftermarket tuners for the big rigs? I personally know EFI Live for my Duramax like the back of my hand, but I only know of Bully Dog for the S60. They claim 6-12% fuel mileage increases. I will take 6%.

love0126
04-16-2011, 03:20 PM
I got to see the truck today. It's definitely idling smoother since the overhead was done. Here are some interesting things we learned from DDEC. I am only gonna look at April for the sake of simplicity here. It says average fuel economy was 5.33 mpg. We are about at 5 right on the nut hand calculated, so DDEC is reading a bit high. The following numbers are not normalized, so the actual fuel economy is lower by about 7% than the numbers below. Average drive load: 60%, avg vehicle speed 59.2 mph. Driving % 43.76->5.48 MPG, Top gear, 74.25%->5.6 mpg, Cruise 45.10% ->5.38 MPG, Speeding 66-71 MPH-> 39.34%, Speeding 71+ MPH-> 18.84%, Highest Speed 77.5 MPH, Stop Idle Time: 53.09%, Engine Utilization 57.60%, Vehicle Utilization 25.21%. So the driver does go above 70 on occasion, but this compares similarly to the engine history totals at 6.7 MPG, so definitely something has been going on. Any thoughts on these numbers?

dzljon
04-16-2011, 08:22 PM
i am still saying cam shaft .. it makes the most since to me....

love0126
04-16-2011, 09:44 PM
I figured if the cam was significantly out of spec, they would have noticed that when doing the overhead. I think it's half mechanical and half driver. We will see when the driver fuels in Indiana tonight what our spot check is for fuel economy. I'm curious how other peoples' DDEC IV numbers come out as. I know she has a bit of a lead foot, but so do other drivers.

Johnp3
04-17-2011, 12:25 AM
Testing the cam timing involves, doing an exact TDC, then measuring the cam lift. It is a spec you check when doing an overhaul. some engines can be out and it only affects performance. if it was overhauled that spec should be in the file. ask!
Doing a valve set you are going buy the cam nothing to do with timing.

love0126
04-17-2011, 01:25 AM
Yes I am aware what involves testing camshafts. my contention is that they are closely related work and I wasn't sure if they did a cursory glance and Mic'ed cylinders 1 and 4 at TDC as the valve adjustments calls for.

love0126
04-17-2011, 01:48 AM
New fuel economy is 5.41 MPG first 600 miles.

theakerstwo
04-17-2011, 02:18 AM
Testing the cam timing involves, doing an exact TDC, then measuring the cam lift. It is a spec you check when doing an overhaul. some engines can be out and it only affects performance. if it was overhauled that spec should be in the file. ask!
Doing a valve set you are going buy the cam nothing to do with timing. In 98 there was alot of engines for some reason came from the factory one tooth off and did not have a problem but our rule was when we do a diamond seal we check the timing.That how we found them and waranty dept was aware of it.But if the jakes hang in the bore it can have a problem.
I mean it may not get good fuel mileage or power but they all sound good.

love0126
04-17-2011, 06:22 AM
In 98 there was alot of engines for some reason came from the factory one tooth off and did not have a problem but our rule was when we do a diamond seal we check the timing.That how we found them and waranty dept was aware of it.But if the jakes hang in the bore it can have a problem.
I mean it may not get good fuel mileage or power but they all sound good.

I could see where that could be an issue. This exact engine though has a lifetime average of 6.7 MPG. Something changed after the driver's first trip out. I know she idles the heck out of it. Over 50% of the time, the truck is idling according to DDEC. She also has a lead foot. Over 58% of the time, she is running over 65 MPH when she is driving. I know getting an APU and setting the governor would curtail these huge problems. This is getting ridiculous. We can't afford to keep idling the truck. DDEC IV indicates it has been consuming 4 gallons per hour idling. That's 16 bucks out the tailpipe per hour. :( The problem is we can't afford an APU right now.

love0126
04-17-2011, 08:23 AM
I re-checked some of my numbers from earlier. The truck has historically used .35 gallons / hour idling. It has recently been idling at .23 gallons / hour idling. I had my numbers inverted. It still seems rather low for a consumption amount. Other than a loss of compression, I cannot think of anything that causes that much of a drop in fuel consumption at idle unless the truck has injectors that are spitting out more than DDEC thinks is happening. Other considerations. The truck has an historic 6.7 MPG average at 56.6 MPH at 47% load. Lately the truck has been doing 5 MPG average at 59.2 MPH at 60% load. If one does the ratio, one gets 5.25 MPG for an expected average. DDEC thinks it's getting 5.33%. Does it seem too coincidental that the load percentage offsets the fuel economy almost exactly so? Does anyone know how DDEC arrives at its load calculation? I want to see if she's just always heavy, or if there is actually an underlying condition causing the engine to compute it is under heavier load than it is based on computer algorithms.

9200IH
04-17-2011, 11:40 AM
You mention you would like to see some other guys numbers.

1996 12.7 set @ 485HP 1,192,000 miles, new injectors @ 998,000
I am the driver, no idle except to cool down motor to shut down (Espar Bunk Heater) Still have blended fuel up here. Flat Bed with 45/48,000 on deck. Last fuel up 1/3 dead head rest loaded, 58mph, I try to shift at or below 1500sometimes that is not possible. 7.93mpg figured at pump not dash display

Mike

theakerstwo
04-17-2011, 12:48 PM
I could see where that could be an issue. This exact engine though has a lifetime average of 6.7 MPG. Something changed after the driver's first trip out. I know she idles the heck out of it. Over 50% of the time, the truck is idling according to DDEC. She also has a lead foot. Over 58% of the time, she is running over 65 MPH when she is driving. I know getting an APU and setting the governor would curtail these huge problems. This is getting ridiculous. We can't afford to keep idling the truck. DDEC IV indicates it has been consuming 4 gallons per hour idling. That's 16 bucks out the tailpipe per hour. :( The problem is we can't afford an APU right now. The engine does not burn 4 gal per hr but if it has 50% time then that can make a big differece. You can have the idle shut down enabled in the ecm so it will not idle no longer than you set the time at as foe as you the owner not the driver. And it can be pasword preteched.

theakerstwo
04-17-2011, 12:53 PM
I learned long time ago the dash display is on a esitmate of fuel burn.It has a map of all condition and should be doing what it says.The driver will be the one that checks the fuel burn and miles run.

love0126
04-18-2011, 04:49 AM
Yes I agree the display can be wrong. I calculated it to be off approximately 6% based on average fuel economy versus the last 20,000 miles run. I should also add that I re-checked my figures. The average fuel burn is actually about .37 gallons/ hour at idle historically. This driver is actually at .25 gallons / hour. She always sets the idle at 900. The only other thing I can see happening here is that the air filter is plugged a bit. Just replaced it 20K ago, but maybe it sucked up enough of its own blowby to cause it to clog up. That said, is it possible that an air filter can cause the truck to lose fuel economy but not substantial power?

love0126
04-18-2011, 05:01 AM
You mention you would like to see some other guys numbers.

1996 12.7 set @ 485HP 1,192,000 miles, new injectors @ 998,000
I am the driver, no idle except to cool down motor to shut down (Espar Bunk Heater) Still have blended fuel up here. Flat Bed with 45/48,000 on deck. Last fuel up 1/3 dead head rest loaded, 58mph, I try to shift at or below 1500sometimes that is not possible. 7.93mpg figured at pump not dash display

Mike

I like your numbers a lot better. We are running 9% deadhead with the new carrier, otherwise hauling lots of french fries, so sitting at 80,000 most of the time. I think my biggest concern is why we're low for economy all across the board. She's barely driving faster than you, albeit loaded at 80,000 90% of her miles and getting a full 2.5 MPG less than you hand calculated. I hate to put a governor on there to help out, but I may have to have it done till we can find the cause. At least we're up 10% after the overhead was done.

379Longhood
04-18-2011, 02:12 PM
Best way to fix driver habits is to make good milage pay them, then they learn to run 55in a head wind, back out one gear on hills. roll on the throttle instead of stomping it. if idling parked instead of having one more blanket on. the missing fuel milage bonus might help your bottom line.

Johnp3
04-18-2011, 07:28 PM
Best way to fix driver habits is to make good milage pay them, then they learn to run 55in a head wind, back out one gear on hills. roll on the throttle instead of stomping it. if idling parked instead of having one more blanket on. the missing fuel milage bonus might help your bottom line.

Another habit that really saves fuel is when cresting the hill going slow over the top and letting gravity help with increasing the speed. I see it every day drivers going full throttle up a grade to full Jake's. No one ever wants to coast.

love0126
04-18-2011, 07:36 PM
What are some of the bonus structures you guys use to get drivers to behave better? Like giving them like a couple hundred a month if they beat our 6 MPG goal?

Johnp3
04-18-2011, 08:41 PM
That is way above my pay grade, the variables are fuel in the winter, temperature, weather, weight, time sensitive loads, log management, trailer placement behind the cab. I know a bonus that can not be achieved is worse than none.
Other things you want to test is the rolling resistance of the unit, I use to have a back road that I would take a truck down and at a certain point take it out of gear and coast. I knew how many telephone pole a normal one passed when starting at 30 MPH. I did it with lots of units, and with an infrared temp gun would find dragging brakes, bad bearings, all kind of things that caused resistance.
Just a thought!

love0126
04-18-2011, 09:10 PM
That is way above my pay grade, the variables are fuel in the winter, temperature, weather, weight, time sensitive loads, log management, trailer placement behind the cab. I know a bonus that can not be achieved is worse than none.
Other things you want to test is the rolling resistance of the unit, I use to have a back road that I would take a truck down and at a certain point take it out of gear and coast. I knew how many telephone pole a normal one passed when starting at 30 MPH. I did it with lots of units, and with an infrared temp gun would find dragging brakes, bad bearings, all kind of things that caused resistance.
Just a thought!

I like the idea about checking rolling resistance. As far as bonus structure, my initial feeling was to base fuel economy bonus on the base 6 MPG. The equation I came up with gave her half the fuel savings above 6 MPG (aggregate fuel economy) as a monthly bonus. I haven't run it by my business partner yet though. Apparently this driver is making him mad over something. He didn't elaborate in a voicemail he left me though. All he said is he is gonna put his foot down on something. As far as load characteristics, she almost always heavy. The trailer is actually sucked up pretty close to the tractor. Just enough room on the catwalk to get at the reefer panel. The one habit I want to change is her 18% of driving time above 71 mph. She spends 60% of her driving time over 65.

379Longhood
04-18-2011, 10:57 PM
Going fast burns fuel , wind resistance increases at the square of the speed increase. so that may be a big one, and soft cresting hills as John mentioned helps a lot, letting the truck run free for the bottom of valleys (within reason) helps too. I would think 1/3 of the savings should be good incentive. and are you checking tire pressure often. even running with the defrost on when you don't need it causes the A/C to cycle and wastes fuel.

love0126
04-18-2011, 11:04 PM
Going fast burns fuel , wind resistance increases at the square of the speed increase. so that may be a big one, and soft cresting hills as John mentioned helps a lot, letting the truck run free for the bottom of valleys (within reason) helps too. I would think 1/3 of the savings should be good incentive. and are you checking tire pressure often. even running with the defrost on when you don't need it causes the A/C to cycle and wastes fuel.

Yes, I'm aware of the square relationship. That's why I think the .1 MPG rule of anything over 60 is a bit of a generalization. I'm not sure of her usage of the Jakes on downhills. Tire pressures were all good last time I checked a month ago. It just got new tires on about 2 months ago. I will check them again when I see it. Hopefully we can get her to quit abusing the fuel economy. I'm sure it's at least half driver with respect to the bad fuel economy. I've never known a truck to get good fuel economy over 70. Ever. :)

Johnp3
04-19-2011, 12:03 AM
When I drove full time, we were grossly underpowered and only used the AC on down hill grades. In the rolling hills even turning the fan on going down hill saves fuel.

love0126
04-19-2011, 01:10 AM
When I drove full time, we were grossly underpowered and only used the AC on down hill grades. In the rolling hills even turning the fan on going down hill saves fuel.

It's also amazing what neutering an engine will do to fuel economy. I know a guy running a C-15 detuned to 325 HP with half empty miles hauling turkey manure is getting 4.4 MPG. The EGT's are always high because they have the turbo turned way down, and the rev limiter keeps the engine out of half of its most efficient range.

love0126
04-20-2011, 12:41 AM
Preliminary DDEC IV readings are at 6.4 MPG for the last 3/4 tank. It was reading in the 5.6 range when we calculated 5.41 last time. Historically DDEC IV has been optimistic by 6%. That still leaves us over 6.1. With that said, she will be almost right at 6 MPG when she fuels. The biggest difference is running in Ohio versus dropping south to Arkansas. The speed limits are lower in Ohio last I checked.

love0126
04-20-2011, 02:47 AM
I got the odometer readings back and it looks like we didn't quite break the 6 MPG barrier, but we were at a much better 5.91 MPG. Still, I see room for improvement. Even though the air filter only has 20K on it, I might change that too. Maybe it got some oil in it... What do most of you guys change your air filter at?

Johnp3
04-20-2011, 04:05 AM
You should have a minder on the air filter, If you take it out clean the housing and be sure the flactuator, rubber lips, valve is in the housing. That keeps the hot air out of the intake.
If you do not have a minder get one I recommend changing the filters every year in the spring, when the dirt is off the roads, or on a Freightliner anything above 12inches.
Cleaning the housing is very important to restriction and cleaning the gasket surface, is important to the sealing.

love0126
04-22-2011, 02:02 AM
I can't remember seeing a vacuum gauge for the air filter in the cabin, but I do know there is a hose coming off the air box. I think that may be the least of our concerns at the moment. The Check engine light came on today and the oil pressure shot way up. The driver said it's at 60, which if I remember right means the gauge is pegged. Has anybody ever had a s60 do that? Kinda scary, but I'm thinking sending unit.

love0126
04-29-2011, 05:19 AM
I wanted to do a quick update to this post. We put the governor on the truck at 65 MPH as of yesterday. We went through the past several tanks of fuel over the past two weeks. It appears when she was in slow states, she was easily in the 6's, but in 70 MPH states, she was around 5.2 MPG. Her speeding hadn't changed much since I talked to her, so we governed it. We will see what it looks like from here on out, but her average fuel economy has gone up the past couple weeks to around 5.6-5.7 MPG. We are betting we will be at 6 - 6.1 MPG next week. The driver was mad, but we told her flat out we couldn't even pay for the truck's repairs at the freight rates we've been getting with the fuel so darn expensive! She did seem to understand that at least. This is still a good .5 MPG less than we would expect from this engine combo. I'm gonna try mixing in some heavier oil at the next oil change to see if maybe the compression is getting low. The blowby is not bad, but we are open to anything at this point.

theakerstwo
04-29-2011, 10:01 AM
I wanted to do a quick update to this post. We put the governor on the truck at 65 MPH as of yesterday. We went through the past several tanks of fuel over the past two weeks. It appears when she was in slow states, she was easily in the 6's, but in 70 MPH states, she was around 5.2 MPG. Her speeding hadn't changed much since I talked to her, so we governed it. We will see what it looks like from here on out, but her average fuel economy has gone up the past couple weeks to around 5.6-5.7 MPG. We are betting we will be at 6 - 6.1 MPG next week. The driver was mad, but we told her flat out we couldn't even pay for the truck's repairs at the freight rates we've been getting with the fuel so darn expensive! She did seem to understand that at least. This is still a good .5 MPG less than we would expect from this engine combo. I'm gonna try mixing in some heavier oil at the next oil change to see if maybe the compression is getting low. The blowby is not bad, but we are open to anything at this point.
Just guess here but sounds like your new to trucks and drivers.

Johnp3
04-29-2011, 03:58 PM
I can guarantee you that thicker oils will definitely not help with mileage. The oil life is easy to check the oil level has to be checked every day, when it starts using oil that is the 1/2 life change it at twice that distance. I am not a believer in long oil changes, and it does effect fuel mileage. The older the engine the shorter the change interval will be.
In my experience Detroit's do well on Rotella, and Cummins like Delo 400

love0126
05-05-2011, 03:56 AM
I can guarantee you that thicker oils will definitely not help with mileage. The oil life is easy to check the oil level has to be checked every day, when it starts using oil that is the 1/2 life change it at twice that distance. I am not a believer in long oil changes, and it does effect fuel mileage. The older the engine the shorter the change interval will be.
In my experience Detroit's do well on Rotella, and Cummins like Delo 400

I agree that Detroits like Rotella. That's all we use. It seems like it starts using oil around maybe 6-7K on the oil. We typically change at 12-15K.

love0126
05-10-2011, 01:43 AM
I figured I would post the updated fuel economy figures and see what everyone has to say...

Before the April 15 overhead tuneup: 5.02 MPG over 5055 miles.
After the overhead and before the governor: 5.47 MPG over 4830 miles. Since the governor (65 MPH) May 28: 6.00 MPG over 3484 miles.

We changed the airfilter, as it looks like it had gotten wet and had been on since October. Otherwise, we checked the tire pressure, and in general it seems to be running very well. I'm still disappointed we can't seem to hit 6.5 MPG like so many of these S60's seem to do. We just did an oil change, and sent in a sample for analysis just to make sure nothing is going on that is deleterious to the health of the engine. There doesn't appear to be any brakes hanging up at all, and we didn't notice any bearings that were catching when we jacked up each axle to check. So I will throw it out there... Anything else I need to do?