I have a turbo question - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 16 (permalink) Old 10-10-2007, 09:49 PM Thread Starter
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I have a turbo question

this is my first diesel and i was told you need to let the turbo cool bown after a long drive?? If so how long is a long drive?? and how long to let it cool???
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post #2 of 16 (permalink) Old 10-11-2007, 12:29 AM
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Quote:
Originally Posted by chevy boy
this is my first diesel and i was told you need to let the turbo cool bown after a long drive?? If so how long is a long drive?? and how long to let it cool???
TRUE! and not just after a long drive, it is necessary after ANY drive. Temps can reach 1200* after a short run.

You should let your turbo cool down to 300* (pre turbo) before shut down. If you don't do it, the oil trapped in your turbo bearings can turn to "coke" and damage your turbo bearings.

The only way to truly know shut-down temp is by purchasing a pyrometer and making sure it's at 300* or cooler before you shut her down.

I have owned a bunch of trucks with pyro gauges but do not have one in my new GMC. Instead, I always let my truck idle 2-3 minutes then shut it off. I'm hesitant to drill into the exhaust manifold and cluttler-up my interior with aftermarket stuff.
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post #3 of 16 (permalink) Old 10-11-2007, 12:53 AM Thread Starter
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ok did not no that thanks for the info
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post #4 of 16 (permalink) Old 10-11-2007, 01:30 PM
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If you have been driving unloaded, at 2000 rpm, and you pull over, the turbo has not experienced more than 2-3 psi at that point, and it is not hot.

This is a water jacketed turbo, and most cooldown efforts are mainly a waste of gas, and serve no purpose, because there is not enough heat to conduct. OTOH, if you pull over hot, like after pulling a grade, it seems justified. But for daily driving in cool weather, it is not helping anything.

One thing the water jacketed turbo relies on, is coolant evaporation. The latent heat absorbed when the coolant heats to a point where it can evaporate (around 260 F) is enormous and will quickly knock down the conducted heat energy. This latent heat absorbtion at 260 degrees keeps adjacent parts well under coking temperature. As it cools, the vapor recondenses, again at 260 degrees. It is a trick idea.

All in all, there is no real advantage in idling in most cases. But whatever you decide, pre-turbo EGT is not the barometer of oil condition or turbo heat. The EGT could be 400 while the turbo is cherry red. Use oil temperature, if anything. Or use post-turbo EGT.

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post #5 of 16 (permalink) Old 10-11-2007, 08:23 PM
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So if my pre-turbo probe is mounted just before the turbo (just a few inches), it's "not the barometer" of turbo heat? It might not be perfectly accurate, but I would disagree with it not being useful.

That seems like a heck of a lot better indicator of turbo temps than nothing at all and served as my barometer. I've never losing a turbo in the over 15 diesel powered trucks I've owned over the years. I attribute that to a moment of cool-down after running my trucks. Conversely, I've seen diesel newbies replace turbos prematurely from shutting them down before proper cool-off.

I would bet that 80% of all diesel truck owners with EGT gauges rely on the 300* pre turbo shut down temp rule of thumb as the time to safely shut down. Maybe it's not dead accurate, but other than having the probe drilled into the turbo, it's better than guessing.

Idling a diesel truck before shutdown is a practice used by truckers & heavy equipment owners that has been done since the advent of the turbo diesel engine and continues today.
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post #6 of 16 (permalink) Old 10-11-2007, 11:59 PM
 
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Not sure about you but my oil temp follows my water temp? how will you know if it's hot or not? I guess you mean an actual oil temp probe on the return side of the turbo??
I'll idle a little if I've been working the truck. If just driving around town I usually turn it off since my EGT's are already down by the time I park.
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post #7 of 16 (permalink) Old 10-12-2007, 12:15 AM Thread Starter
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o my if i wasnt confused before i may be now?????my turbo has coolant running through it??it is a 07 lbz i new about the oil but the last ones i have worked on didnt have coolant running through them
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post #8 of 16 (permalink) Old 10-12-2007, 01:38 AM
 
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not through them, around the centersection to keep heat from sinking from the exhaust side to the compresor side and messing with your intake air, and it helps keep the oil temp low by acting as the medium to take most of the exhaust heat

to cool it down for minutes afte straight daily driving is a little much, probably let the turbo spool down and the rpms to level out for like 30-45 seconds, thats all, but any hard driving and it is necessary for a little longer cool down period
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post #9 of 16 (permalink) Old 10-12-2007, 02:56 AM
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On a July afternoon, my EGT will not lower below 400 regardless of how long I idle. That is because the IAT rises when parked, and that keeps EGT high. Yet if I switch off my AC, I can lower egt 50 degrees. Does that mean that my turbo is 50 degrees cooler, by turning off the AC?

I am not arguing, just posing questions. Does my pre-turbo gas temp lower when the turbo is cool enough? No, it lowers when the cylinder cools off, among other things. When reading EGT, you are reading the temp of a gas that has not even been to the turbo yet, so there is no correlation at all.

I know it has been done this way forever, I hear you Duke. I'm saying it doesn't make sense, though if you had a stopwatch and no egt gauge, you would have very similar results.

I too just make it a point to idle in, it was an old pilot trick also, because those turbos need to cool off slow. They were not water cooled however.

Anyway, not picking on any particular technique, just making for a thoughtful and provoking discussion.

Michael
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post #10 of 16 (permalink) Old 10-12-2007, 04:46 AM Thread Starter
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sorry if i started somethang im still lost
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