Duramax 3.0 Coolant Leak

Cobra03 · Mar 22, 2025

Douglee25 said:
I have the dreaded 3.0 coolant smell from the passenger side of the truck.

The other day I pressurized the cooling system to see if I could find the leak.

At 11-13 psi on the gauge, I hear what sounds like a relief valve behind the turbo and then coolant blows out and drips everywhere on the ground. I couldn't even get the system to 20 psi.

I can't see much without pulling the intake tube, so I took it into the shop for a warranty repair.

I'm not feeling confident about the tech's diagnosis because I didn't see any fingerprints on my dusty engine - literally doesn't look like he touched anything.

They claimed it was a bad expansion tank and a couple of lines. When I told them the leak was from the passenger side, they brought it back into the shop and they added the turbo to the list for replacement??

From the diagrams, I see nothing that resembles a coolant relief valve behind the turbo. Just some coolant lines, the EGR setup, etc.

Any ideas?

Curious What year , my buddy has a 23,

Douglee25 · Mar 22, 2025

Cobra03 said:
Curious What year , my buddy has a 23,

'24...bought in Sept.

BlueBrute · Mar 23, 2025

Like I said earlier in this thread, a friend of mine had this coolant leak in his Chevy High Country. They completely gutted the interior to "fix" the leak. That lead to a few other problems not related to the original complaint. It was in the shop for weeks. Then the day after they got it back and everything was "fixed" they could smell coolant again. When it was all said and done that truck was so screwed up he just went and traded it off. It's so discouraging.

Douglee25 · Mar 23, 2025

BlueBrute said:
Like I said earlier in this thread, a friend of mine had this coolant leak in his Chevy High Country. They completely gutted the interior to "fix" the leak. That lead to a few other problems not related to the original complaint. It was in the shop for weeks. Then the day after they got it back and everything was "fixed" they could smell coolant again. When it was all said and done that truck was so screwed up he just went and traded it off. It's so discouraging.

I hate hearing things like this. So frustrating when you spend the money you do. I traded in a 2018 suburban because it was getting up there in mileage (I put on 25k miles/year). My whole rationale was to avoid downtime with the vehicle and have something with an actual warranty. Ha!

Anyway, I called the service advisor twice yesterday. He never called back. I guess I'll have to connect with him on Monday.

Douglee25 · Apr 7, 2025

Update 4/7 -

Truck went back in the shop. Shop called and said everything stayed pressurized. They couldn't find any leaks. I asked if they would mind having the shop foreman call me. Two days later he called me back. Super nice guy & knowledgeable guy for the record. I explained to him what I been through to date and he was well aware of the history. I asked if he would demonstrate to me the system holding pressure, to which he replied absolutely. So we setup a time and I arrived to the dealer. He already had the rig hooked up to the gauge and pressurized. I spoke with him for 15-20 mins and the gauge didn't drop 1 psi. I said it's possible I have a bad gauge, however, he said it's not likely. He said it's probably the O-ring on the adapter that seals on the overflow tank (you need a special adapter to hook up to the pump/gauge). I saw that they had filled the tank all the way up past the max fill line with water - I'm assuming they did this to help seal their gauge O-ring. He mentioned that they also added the UV dye in case it does leak in the future they should be able to find it.

Satisfied, I took the rig home and have been driving it a week or so.

I will keep monitoring things...