Replacing the waterpump on an LB7/LLY Duramax - Diesel Truck Forum -
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post #1 of 6 (permalink) Old 12-26-2008, 12:44 AM Thread Starter
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Replacing the waterpump on an LB7/LLY Duramax

Since I had such an adventure replacing my water pump, I thought I'd write it all down. Maybe it will help someone down the road. Many thinks to Eric Merchant and his employees, to Adam (Malibu795) for much of the initial info (including the 1/2" extension in the flywheel trick), and also to many other people who have taken these instructions and added to them over the past year. I did not take any pictures, as there was no time. It took me 6 hours.
Your procedures and speed may vary.



water pump (with housing or not)
both pump o-rings, the gasket for the oil cooler feed tube, o-ring for the lower thermostat pipe connection (these should be with the new/remanned pump)
Optional: 4" piece of 3/8" heavy-duty hose for thermostat bypass (behind the balancer) and a new o-ring for the upper thermostat pipe connection (Merchant used an LB7 injector sleeve o-ring, they are tougher than the regular ones)
4 or 5 gallons of 50/50 Dexcool or equivalent ( I used the Peak Global Dex-compatible stuff)

You'll need these tools:

3/8" and 1/2" ratchets and a 3/8" extension 16-20" long
3/8" rattle gun
10,12,14 mm sockets
12mm wrench
15mm 3/8" SWIVEL socket (for the starter bolts)
screwdriver, retaining pin pliers or wire nippers
Large piece of heavy cardboard, thin plywood or sheet metal (to protect radiator -- in order of preference, worst to best)
air hammer or pipewrench/cheater bar or 1 7/8" wrench (for fan nut)
3/4" ratchet/cheater bar/36mm 12pt socket for balancer (can also use 1-7/16 socket)
Torque wrenchs -- inc one that can go up to 300ft lbs (3/4")
KentMoore J-44643 flywheel tool or something to hold the flywheel in place (1/2" extension may work)
large pan for coolant
something to stand on while working
dielectric grease for o-rings
A supportive friend and plenty of beer.

1) Remove pass side tire. Remove inner fender liner. I also disconnected the negative battery cables.

2) You dont have to take the starter OUT, but it does have to be separated from the engine. Using the 15mm swivel on the 16" extension with the air gun helps greatly here. Top bolt is easy to get to. Bottom bolt is have to go through the small area between the upper and lower control arms, behind the shock. Its just next to the diff mount. Starter will only move enough to free it from the block. Its a tight fit in there.

3) If you have that J-44643 tool, install it in place of the starter, using the starter bolts. If not, try to get a 1/2" extension into one of the holes in the flywheel. Make sure the extension is seated well, as its got to hold the engine still so you can get the balancer off. Other people have removed the inspection plate from the drivers side of the bellhousing and used a prybar, large screwdriver or extension wedged in between the converter bolts to lock the crank against the trans bellhousing. ZF trans owners may be able to put the truck in 6th gear with the clutch engaged (obviously with engine OFF) to hold the engine against the bolt's torque. Both these "other" methods are to be used at your own risk.

4) Time to drain coolant. This is an ugly messy job. You loosen the radiator cap to regulate the flow of coolant. The Dmax radiator drain is just next to the lower intercooler boot on the pass side. Its a simple plastic twist fitting. The messy part comes from the fact that theres no petc*ck integated into it. You loosen it up and it sprays coolant 360*. Make sure you have a large, deep pan.

5) As the coolant is draining, you can start working underhood. You'll appreciate the stand now. I used a 3 foot bar stool. I removed the top plastic rad cover to get at the upper fan shroud. Remove the TCM -- two 10mm bolts and unplug it. Set it aside. To remove the upper fan shroud, there are two other 10mm bolts along the top, and 4 push pins connect the upper and lower fan shrouds. Use the nippers or the pin pliers for the pins. Unhook the A/C line from the shroud clip. Remove fan shroud.

6) Install the cardboard, plywood or sheet metal over the engine-side of the radiator. If you dont do this step, you had better be EXTREMELY careful from now on. Proceed at your own risk.

7) Remove the fan. It'll be tough if its never been removed before. Have your helper use the 1/2" ratchet to tighten the belt. You have to hold the pulley against the loosening force. When you're looking at the engine from the front, you want to loosen the nut toward the pass side of the truck. The air hammer is a life saver here. Just hammer the left side of the nut with the A/H to loosen. If you have to use a wrench, it'll take some effort. Maybe using some liquid wrench between the nut and pulley will help. You'll get it. After you loosen the fan, it'll just twist careful when you get to the end of the threads. The fan weight will want to swing it into the radiator.

8) Remove the serpentine belt.

9) I removed the fan support/pulley after this. There are five 14mm fasteners, 3 bolts and 2 nuts. It pulls straight off. Leave the rubber insulation in place if it stays on the block.

10) Hope you ate your Wheaties, cause now its time for the balancer. The 3/4 ratchet, cheaterbar and 36mm socket are the only way, unless you remove the radiator and use a high-torque rattle gun. You may need your friend's help to get it started. 260ftlbs is a heck of a pull. After you remove the bolt, the balancer should slide right off. SHOULD. If it hangs up, just work it back and forth and it'll come. Watch out, its heavy. Again, this is where the cardboard comes the radiator as you pull the balancer off.

11) By now, the coolant should be low enough to work on the water pump.
Remove the lower radiator hose. The clamp is integral to it. You may have to use a pick tool or the screwdriver to separate it from the pump.

12) Loosen the two 12mm bolts that hold the thermostat pipe to the top of the water pump. You dont necessarily have to remove this pipe to get the pump out. I wanted to replace my bypass hose during this install, so I removed the pipe. If you do remove the pipe, make sure you have a replacement o-ring for the upper seal. Like I stated above, an LB7 injector sleeve o-ring works perfect. If this o-ring gets cut, you'll have a big mess later on. More on that later.

13) There are two 12mm nuts holding the oil cooler tube to the back of the pump. IIRC, you can access them through the drivers side wheel well, or you can be a contortionist like me and get them from under the truck and from the side. Its not an easy task. They are not torqued on very tight, thats a plus.

14) Remove the water pump. There are two 12mm bolts, one on top and one on the right side. They are two different lengths, so remember which one went where. There is also a 12mm nut on the lower left. This PITA nut is the only reason the balancer had to be removed. The pump needs to be wiggled out. You'll be amazed at all the coolant still in it. If the oil cooler tube gasket stuck to the tube, make sure to pull it off.

15) If your replacement is just the pump (no housing), there are three 12mm bolts holding the pump and housing together. Dont forget to lightly lube the o-ring with dielectric grease before you put the pump back together. Torque the bolts to 16-20ftlbs.

16) Install the pump. Dont forget the new gasket to the oil cooler tube. Dont forget the pump o-ring, too (lube lightly). Tighten the bolts and nuts on the cooler tube and pump to 16-20ftlbs.

17) Reinstall the thermostat pipe. Replace the hose if you choose to. Dont forget the o-ring between the pipe and the pump. If you took the pipe out, replace the upper o-ring, and use some dielectric grease on the inside of the thermostat HOUSING, not the o-ring itself. You dont want to roll or cut that o-ring (like i did). The pipe will kind of "click" into place in the thermostat housing. Be very careful not to cut the o-ring, and double check that the o-ring is seated. Tighten the bolts into the w/p to 16-20ftlbs.

18) Replace the Lower radiator hose.

19) Replace the balancer. Torque to 260 ftlbs. I actually went a bit past that...275...I'm paranoid. Blake also showed me the GM torque specs...they say to torque to 74ftlbs, then tighten 105* past that. I think he tried it once and found it was closer to 280-290ftlbs.

20) Replace the fan pulley/support. Torque the bolts/nuts to 45 ftlbs.

21) Replace the serpentine belt.

22) Replace the fan. When you get it snug, use the air hammer and just touch the nut on the right to tighten it. It doesnt need much. The turning force of the accessories fully tighten it back up.

23) Remove the cardboard/wood/sheet metal. Replace the upper fan shroud. Clip the A/C line back in. Replace the TCM. Replace the upper radiator cover.

24) Back to the wheel well. Remove the extension or flywheel tool. Replace the starter. Torque the bolts to 58-60ft lbs. Reconnect the negatives on the batteries.

25) Make sure to tighten the drain on the radiator. Replace the wheel well liner and tire.

26) Fill cooling system. You MUST use Dexcool or a type that is Dex-compatible. DON'T use regular green anti-freeze unless you swapped it completely out sometime in the past! (this involves flushing the entire system twice with plain water and is a real PITA) If you mix the types, you'll end up with a brown goo throughout the system that will cause overheating and a possible blown motor later. I've seen it happen.
There is a 12mm bleeder bolt on top of the thermostat housing. Loosen that bolt. Fill system with fresh Dexcool (or equivalent) until it comes out that bleeder, then tighten bleeder to 16-20ftlbs. Fill the overflow tank to full cold level.

Clear tools, start truck and look for any leaks. Refill coolant tank as needed until all air is out of the system.

If no leaks, then crack open a beer and celebrate.

One other thing....check your oil. If its milky, that means coolant got past the failed water pump seal and mixed in it. I recommend changing the oil.


I went to Autozone and got the big ratchet ($32) and socket ($10). Harbor Freight had the torque wrench ($75). I bought my water pump at NAPA. The only one they had in Michigan was a reman with a lifetime warranty for $68. Not that I wanted to use a reman, but beggars cant be choosers, and a new pump is $225.

This job was a total PITA for me. I at first tried to do it in my garage. But I got to the fan and couldnt remove it, even with an air hammer. So I buttoned everything back up and called Eric. He said to bring it on over (after he got done laughing his *ss off), and that I could use the shop. So I took that Tuesday off work and drove to Holland. Thank God I did. They were extremely helpful, because every 15 min or so, I'd stop and have to think, "OK, what do I do next?" Thats why it took so long.

This is why I stress watching yourself around that upper pipe o-ring.... I had that darn thing break on me during install and didnt know it. Got everything done, filled radiator with coolant, then started the engine and coolant sprayed EVERYWHERE. I had to go back and replace that darn o-ring, which involved taking the front of the engine apart again (except the balancer). I HIGHLY recommend using an LB7 injector sleeve o-ring instead of a "standard" o-ring if you decide to replace it.
Another 2 hours later, I was done. This time, I asked Eric to pressure-test the system before I put the front of the engine together since he has that capability. It checked out fine, so I finished up the install. A total of 8 hours from start to finish. We didnt even have time for a beer afterward, as it was 8pm and I had to get home.

Good Luck.
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post #2 of 6 (permalink) Old 12-10-2009, 10:43 AM
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Replacing the waterpump on an LB7/LLY Duramax

The NHRA techs frown on it too...especially if you just use some spare sheetmetal, old weatherstripping and a single screw to hold it down.

Of course, how many time have you seen the tech guy check under the rear carpet?
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post #3 of 6 (permalink) Old 02-24-2010, 02:55 PM
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Great article. Do you by chance have the part number of those you recommend replacing?
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post #4 of 6 (permalink) Old 03-27-2010, 12:46 AM
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i had my 02 taken in to have the water pump changed out and i had the thing for a week and the thing started leaking.. turns out the o-ring on the thermostst pipe had been cut as stated above, and blew half way out! so i took it back and waited four days for them to tell me it was fine????? i drove it home and guess what?! it started leaking.. ive had it there 3 times still waiting on the word to come pick it up. soooo tired of this crap all because of an o-ring!
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post #5 of 6 (permalink) Old 05-30-2011, 02:40 PM
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Excellent write up sir.

LLY Duramax
EFI Live
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post #6 of 6 (permalink) Old 01-29-2012, 08:41 PM
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This write up has been a great resource for this little project so thank you! As I write this I am on hold trying to track down an oring for that thermostat pipe... I am ready to be finished and here I sit...
travisleddy is offline  

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