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Anyone have issues with a coolant leak the dealer “can’t find”. 


I bought my l5p denali duramax about 6 months ago and have put 15k on it in those 6 months. Mostly used for pulling my 43’ fifthwheel. 


Anyway the issue. At 3k the low coolant light came on and I brought it to the dealer. I was told air had not been properly removed from the cooling system when assembled so they burped it and I was on my way. I was good till 11k miles. At 11k the light came on again and I brought it in. The radiator was replaced, brought it home and started it a couple days later and the coolant light came on. Called the dealer same story burping air out so I topped it off myself. 11k noticed coolant puddle under it and coolant drips on passenger frame rail by front bumper. Brought it in and dealer couldn’t find a leak so I took it home. Two days later the coolant light came on and multiple drips were on the frame.


So at this point I have executive GM involved  with trying to figure it out. A couple things at this point have me worked up. Not one time was I offered a loaner car not once. After the radiator was replaced they put The plastic skid plate one under the radiator and broke it and left it on. 


So now I want a loaner when I drop it off. I wait almost a month before they give in and give me one and bring the truck back in. At this point the over flow is almost empty so it’s not leaking very fast. The truck now has 15k on it. 


I bring it it in and get a loaner car for the first time with 15k on it and the 4th visit in 6 months. Dealer still can not find a leak. I asked them to climb under they truck and look at the frame rail for coolant. He calls back and says it’s dry. So I send my wife to pick the truck up. She drives 15 miles home from the dealer and that’s it. When I got home from work I checked under the truck and it’s dripping coolant. 


So a couple of things so far, executive GM has done not one thing to help me out. I have done everything myself. They don’t return calls and do not return emails. The last time I brought my truck in the dealer refused to give me any paperwork showing that they actually looked at it they just gave me paperwork from my previous visit. 


He service advisor keeps telling me it’s burping out air and it’s residual coolant from the radiator replacement 4K miles ago and 2 months ago. I don’t know what to do. I have lost all respect for GM and their product. 


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Tell them to do a pressure test. But it sounds like it is a shitty dealership. I had a very small leak on my 2014 half ton. It always smelled when I walked around the front of the truck. Even the service manager said he could smell it. But twice they checked and "couldn't find a leak" 

I finally went to another dealership. They did a pressure test, found a leak in the rad and replaced it. Almost two years it leaked until i went to the second dealership. 

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They have done 3 pressure test in the two times I have had it at this dealership. I think the leak is so small it’s not dropping enough pressure to show up. Over 2500 miles it went from the full mark to the light coming on. So it’s very small. I just want them to take the thing apart and look for moisture but all they wanna do is a pressure test. 


It’s to the point now that I had to cancel my 3000 mile round trip Christmas vacation home for Christmas because I didn’t want mu wife and my two young children stranded on the side of the highway somewhere because something came loose and dumped all the coolant out. 

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Duramax Diesel Engine Coolant Leak

postdateicon.pngMarch 27, 2017

2017 Silverado and Sierra models equipped with the 6.6L Duramax diesel engine (RPO L5P) may display a Driver Information Center low coolant message or may show coolant consumption or a coolant leak. These conditions may be due to cooling system leaks or an improper coolant fill procedure.


When diagnosing these conditions, be sure to complete the coolant system leak checks in the appropriate Service Information to verify there are no external leaks. It may take a few engine temperature cycles, from operating temperature to cold, for the coolant level to show a lower than normal level.


TIP: Do not pressure test the coolant system.


Coolant Loss


Check for coolant leaks at the welded flange on the Exhaust Gas Recirculation (EGR) coolant return pipe (Fig. 7) and coolant feed pipe. (Fig. 8)



Fig. 7



Fig. 8


In addition, check the O-ring seal on the EGR coolant feed pipe for a coolant leak. The O-ring may be pinched or rolled. (Fig. 9) It may be necessary to remove the front accessory drive bracket and alternator.



Fig. 9


Coolant also may leak from the coolant hoses at the Emission Reduction Fluid Injector (DEF injector). (Fig. 10)



Fig. 10


Radiator Surge Tank


The radiator surge tank uses two different radiator surge tank caps. The radiator surge tank cap that vents pressure in the event of excessive cooling system pressure is located on the lower outboard side of the radiator surge tank. The radiator surge tank cap that is located on top of the radiator surge tank is where the cooling system is filled. It has left hand threads; turn the cap clockwise to remove the cap and counterclockwise to install the cap. If the cap is turned in the wrong direction when installing or removing it, there may damage to the cap and/or the surge tank.

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I have had it to three different dealerships throughout this whole issue but only one after the radiator was replaced. I was checking the coolant level after a drive yesterday and found a leak where the hose for the overflow tank connects to the top passenger side of the radiator. Surprises me that I can find it but a tech that’s paid good money doesn’t open his eyes unless it’s to look at a computer to tell him if something is wrong. 


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  • 2 weeks later...

So they replaced the clamp with a hose clamp after I pointed it out to them. However I checked it today and coolant is spraying all over the engine bay. Mostly by the battery. Where they put the hose clamp on is still leaking also. And where the coolant dripped off the frame it cleared all the frame protectant off and it’s starting to rust. I can’t get anyone from executive GM to contact me back. The dealership flat out doesn’t give a shit and told me to bring it back to the dealer that replaced the radiator (that’s over a 10 hour drive away). I might just have to get in touch with the atourney general because I’m getting no where with these people. 


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