HVACTech

A month ago was towing my camper 20ft, 3,000 lb. dry 3,800 gvwr. 30 minutes after departure on the way home the engine temperature gauge maxed out and sent a warning to the dash “engine overheating idle speed”. I coast for a quarter mile and the engine temperature corrected. Drove 2 hrs. no issues until idling at a gas station 10 minutes temperature again rose to the max and began to steam under the hood in the area of the coolant reservoir/air filter box. At this time coolant was full. I limped home with the engine temp rising and falling. Immediately quit driving the vehicle. While doing a thorough check of the engine cold found no evidence of coolant leak, however coolant reservoir was completely empty. Added 2 gallon+ of Dexcool and took vehicle to Jeff Gordon Chevy Wilmington Nc. They did overnight pressure test on radiator, passed, said they found water pump to be “noisy” replaced that preventatively. All in all, said they found no issues. Also had full service done and thorough examination of entire vehicle, dealership said car is perfect. A week or so later put the vehicle back on the road towing. Made it 2.5 hrs. suddenly A/C quits blowing cold, engine temp gauge had dropped to bottom (as if not functioning) and oil pressure dropped to very low. Every time the oil pressure dropped there was knocking under the hood. Pulled over, sat for 1.5 hrs, coolant had completely disappeared with only a small amount on the pavement (maybe 12 oz). No signs of major leak. Added 2 more gallons coolant. Started the vehicle, limped 5 miles to campground oil pressure would not dip if I kept the RPMs up, when stopped would fall and knock again. I could keep oil pressure up by going to neutral and revving engine and keeping rpm’s up while driving. Got to campground in SC and had the Tahoe towed back to Wilmington, engine light now on. Jeff Gordon Chevy calls today and says they have driven on the interstate 20 minutes and no issues with the vehicle. Code reader says temp sensor, mechanic says that could be tcm, pcm, but “that doesn’t mean anything” he says. Any ideas what could be going on? Cannot take another trip until we figure this out so vehicle is no longer reliable.

oilcanhenry

If any coolant gets into your motor it will destroy your engine bearings and other things, which will drop your oil pressure. Once the bearings are gone, it's adios to your engine. Pure water takes longer to do this, but if your oil pressures are already down, the damage has already likely been done. Don't add coolant if you drive it, and if you have a radiator cap, put it at half notch so that it will reduce the coolant/water pressure. Pretty sure you have a blown head gasket(s). Likely need a new engine.

HVACTech

Thank you, that is what I am worried about.

So is this an issue that would come and go? (The bearing/head gasket issue you have described) The guys at the dealership are saying the vehicle is showing no sign of any issue since we had it towed there. They have had it for 2 days.

oilcanhenry

Yes. I have no idea what they did. All I know is that it's a blown head gasket or both. Man, I am sorry to give you this bad news, but engines with a blown head gasket(s) are not fun. Don't trust dealerships for this very reason. A motor that ran out of coolant; low-oil pressure and is knocking are, all the signs of
head gasket failure. Going by what you posted, you'll likely need a new, used or rebuilt engine. Once knocking and low oil pressures occur, it's a given. The low oil pressure means the bearings are gone.

All too many are dealerships are dishonest, to say the least. Better and cheaper to have your Chevy towed to a reputable non-dealership. You can find them on YELP. That's where I found mine for things I cannot repair since I don't have a lift . Too, they often will cut labor costs by 10 percent if you meet their definitions.

BTY, I like your handle: HVACTech. I am well versed in working on automotive Air-Contioning Tech myself, assuming you are not or are a Home HVAC technician, which I am not. I let the experts do that.

HVACTech

Thanks so much. I own a mechanical contracting (HVAC) business here in NC. The crazy thing about our issue, the dealership drove it 60 miles and cannot replicate the issue. My wife drove it home yesterday almost 30 minutes with her mom following in traffic and the vehicle showed no indication of an issue. It is the weirdest thing. The issue only shows after 2 hours of towing our camper (again super light). Thank you so much for your help, it is very kind to take the time to offer advice to a stranger. I think we are going to cut our losses on this vehicle, since at this very moment there are no engine lights or codes and the issue can’t be found. I love the Tahoe but should have gone with the 5.7 base model and not got all giddy about this RST 6.2 package.

tech2

oilcanhenry may be onto something. Have the coolant checked for combustion gases.

73shark

HVACTech: Welcome to the forum.

Someone needs to check the oil for the presence of coolant or water. That much water cannot just disappear. That much water can only go out of the cooling system one of three places. That would be into the crankcase, out on the ground through a leaky hose or radiator, or out the exhaust.