Letters and Emails

Published in the April 2011 Issue April 2011 Ask The Expert

Dear DT,

When I decided to become a diesel owner myself I started reading the magazine just to learn more about diesels and how they work. I'm an apprentice heavy-duty mechanic and figure I would eventually learn enough that I could service my own big rig, as I like to call it, never thinking I'd have to reach out for help so soon.

I just bought a 2004.5 (LLY) Duramax diesel about a month ago. It has a cold air intake, 4-inch straight exhaust and a juice with attitude on it. I have put about 1900 miles on it bringing it home (600 highway miles and then in town) when my check coolant level display came on. I looked in the reserve and it was a bit low so I topped it off. After that the headache began. It seems like the coolant was getting air in it. I instantly thought it was a head gasket so I did your usual checks and they came back negative. For example I checked for: coolant in the oil, blowing white smoke out the exhaust, pressure tested the coolant symptom when hot and cold (which held 15 pounds solid) and measuring if there was exhaust gas in the coolant with a tester (liquid turns blue to green). None of these symptoms were there so I started reading forum after forum and most of them pointed towards a head gasket. Some of them also suggested eliminating the juice with attitude just to ensure it wasn't just being finicky. But on a few forums I read there were guys having the air in the coolant, but none of the other symptoms that would say head gasket. I started to monitor the truck closer and the temperature on the gauge was now acting funny. It would all of a sudden run high after I'd throttle hard on the truck and when I let off and coast the truck it would settle in the normal temperature, which was just below 100 Celsius and stay there. The other symptom was the truck would warm up a quarter way up the gauge and the then drop right off to cold. While that was happening I would monitor the cab heat and it would match the gauge (i.e. when the motor temp read cold, the truck blew cold air). I added coolant here and there and every time I'd unpressurize the system, there would be enough pressure to blow antifreeze out of the overflow. I'd get blow over sometimes, but just a small amount. My knowledge tells me that the pressure is only rising slightly above the caps psi which is 15 to cause the blow over but not an excessive amount, i.e., like a head gasket. I would even run the truck for about 25 miles down the highway and it would run fine and stay at normal temp. Through guess and check methods I changed the lower radiator hose because it had a wear spot on it from rubbing on the idler arm, I flushed the system, change thermostats, also replaced the O ring on the upper radiator pipe that attaches to the thermostat housing (just because a dealer suggested it), radiator cap and of course bleed, bleed and bleed the system. But the air is still there! I have taken it to a few mechanics in the small city I live in and they don't think it's a head gasket but also don't have the experience in diesels to tell me what is wrong for the fact it's not a diesel city. I don't really want to pay someone to use my truck as a learning experience and end up with a large bill to pay do to it. The next close repair garage is eight hours from here and I don't want to take the chance by driving the truck that far. I also called GM Canada and they wouldn't give me a diagnostics because they didn't want to mis-lead me. I asked the dealership if they thought the turbo or EGR could be introducing air in the system and they straight out said they didn't know. The only issue they dealt with like this was a clogged overflow and a cracked block which scares me. All in all this entire problem has been one big headache and I have only owned the truck for about seven weeks.

Thank you for taking the time to read this and I hope you can help.

Patrick Hayes

Thompson, Manitoba



I've talked to the Duramax guys I work with regularly. If the head gasket has checked out ok, our next assumption would be a failed water pump. On the LLY, the gears can come out, preventing the pump from circulating coolant properly for good cooling system function. It would explain the fluctuating coolant temps and creating pressure in certain sections of the cooling system where the coolant has overheated. A faulty EGR would cause white smoke. Head gaskets would also explain most of your truck's symptoms, but you've checked those out. Cam Hulse, one of the techs we talked with, has seen a couple instances where the LLY head has developed a hole in it, allowing the exhaust to pressurize the cooling system much like a failed head gasket would do. If a previous owner has mixed green antifreeze with the orange Dexcool antifreeze, the two create an acidic environment that eats away at the aluminum head. Did you check the coolant that was in the truck when you bought it, or do the flush first?

We would recommend you get it somewhere reputable that can pull the heads and replace the head gaskets first, as this is the most common problem that covers what you are going through. You can also have the heads inspected then. After that, replace the water pump. I can't really recommend any shops in your area. We've had good experiences with a few in Alberta and BC, but haven't dealt with anyone your way.

Let me know if you have any other questions. I can give you a number or email for Cam Hulse at Adrenaline Performance if you want. -Ed.


Dear DT,

I am trying to find a diesel pickup, but I don't know where to start looking. I know I want a 2000 and newer, but I don't know which of the big three to choose from. And I'm deployed to Iraq serving in the army, so I can't just call dealerships. My goals for the truck is to be able to pull anything, haul anything, go anywhere, do anything, and make over 1,000 ft-lbs of torque, a 4-inch lift kit and stacks. Which of the three should I go with? Which one is a good base to start with?

Jared Dwight

Via Email


First off, thanks for your military service. As for the question on the trucks, here's our take:

Making a truck bulletproof at 1,000 lb-ft of torque (about 525 horsepower) isn't too difficult. The Ford 7.3L Power Stroke is probably the hardest one to get there and maintain its drivability. Once they are built with enough fuel and large enough turbo to put out over 500 horsepower, they become hard to start (especially in cold climates) and a little more difficult to maintain, as the high-pressure oil injection systems aren't necessarily suited for that kind of power output. Not saying it can't be done and done well, but it's easier and less expensive to get that kind of performance out of a Duramax or Cummins.

For the Cummins, we would recommend at least a 2002 or newer model. For a Duramax, any year would be good to start with. You'll run into things that need upgraded quicker on the 01-04 LB7 engines than you would on the 04.5-05 LLY, like injectors, injector hold downs and cups and head studs. On either Cummins or Duramax, you'll need to build the transmission and upgrade the turbo for 500 plus horsepower applications. -Ed.

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