Another coolant leak thread

[mattt]

Hi all, I have this small coolant leak that is driving me crazy because I can't find it. Some background info: 2004 Tahoe w/ 340k original mileage, all new 6.0 LQ9 installed 2022(maybe 6k miles so far in 2023), new heater hoses & T's, new coolant reservoir, new radiator, newer water pump moved from old 5.3. The leak is small enough that it is not hitting the ground or showing itself from water evaporating and leaving the white residue. But it is bad enough that I'm carrying pre-mixed coolant with me to top it off every 10 days or so.

Is there a way to determine if the head gaskets on the new engine are the culprit? I pray they're not. Oil looks clean. Isn't there some sort of exhaust gas test that can be done on coolant? How do you get a coolant sample for that test?

I suspect the heater core since it is original to the Tahoe, but there is no coolant leak from the evaporator drain, unless the A/C is on. With the A/C on, the puddle from the evaporator drain and surrounding area is very substantial....like A LOT! I believe the evaporator drain tube is directly below the A/C dryer, correct?

Occasionally I get a sweet or pungent smell from the dash vents right at start up and when I first take off but it goes away in ~1 minute or less typically. If the heater core is leaking wouldn't it present itself as a leak out of the evaporator drain tube?
Thanks

 

[Scottydoggs]

you can pressure test the cooling system. parts store should have it for the free rental deal.

 

[blackelky]

I wonder if it could be thermostat housing or maybe the waterpump not seating correctly with the gasket

 

[Fless]

Get a light and a mirror and carefully inspect the underside of the water pump; there should be a weep hole. Look for witness streaks where coolant has leaked out and dried in the wind, before it could drip.

 

[mattt]

Thanks for the responses. I checked the water pump weep hole but I will check again. Years ago that is how I found the original water pump was leaking, the big white stain on the bottom half of the pump.

Is the evaporator box drain where I mentioned, below the A/C dryer?
If the heater core is leaking would it be dripping from the evap/heater box?
Any ingenious way to check the heater core for leaks without completely disassembling the dash and evap/heater box?

 

[Big Mama]

I’m sure you checked but I didn’t notice where you looked for damp carpet? Otherwise the pressure check is the way to go. It’ll show the leak. Hopefully in a place that’s easy to see and get to.

 

[mattt]

Okay, I did the pressure test with the rental tool and the system holds 15psi with no visible leaks. Then I started the Tahoe and let it run with the 15psi still holding. As it ran longer, I noticed something that might be dreadful. The pressure increased the longer it ran. Is that the concern that I think it is, engine compression pressurizing the cooling system?

I keep forgetting to pull the passenger floorboard mat and check for wetness, I'll check it today. If the heater core is leaking is that where the coolant shows itself? Does it not go out the evaporator drain in the firewall?

 

[OR VietVet]

You put a new engine in and did not install a new water pump?

 

[mattt]

You put a new engine in and did not install a new water pump?

Yes, the water pump was 7 months old so it was still new. The pump isn't the problem.

 

[OR VietVet]

Did not think it was the problem. I was just surprised at using a "used" water pump. The second you tighten it to the block, it is used. I personally like to use new when there are moving parts and bearings and seals involved. Your engine, your call.

 

[mattt]

Thank you for the peanut gallery comments. I was surprised with some of your calls in your posts and offerings here as well. So like you said your deal, your call. If you have something to add in regards to the issue I'm dealing with, I appreciate your post.

 

[OR VietVet]

Well, I do like salted peanuts, so here goes. With the coolant hose tees, I am assuming you have rear heat. Check there for seepage when pressure tested.

With the pressure test results you stated, I fear the head gaskets too. There are a few chemical kits you can get at a parts store and do the instructed chemical sniff tests for exhaust gases in the coolant. The 6.0 engine is not supposed to be involved in the Castech cracked heads problems. Look at the "boss" at the front of the passenger side head and see if it says "317". That should not be in the "possible cracked head" category but could still have head gasket problems.

 

[Big Mama]

Any luck with the passenger floor board?

 

[mattt]

Any luck with the passenger floor board?

Bone dry.

 

[Donal]

Okay, I did the pressure test with the rental tool and the system holds 15psi with no visible leaks. Then I started the Tahoe and let it run with the 15psi still holding. As it ran longer, I noticed something that might be dreadful. The pressure increased the longer it ran. Is that the concern that I think it is, engine compression pressurizing the cooling system?

I keep forgetting to pull the passenger floorboard mat and check for wetness, I'll check it today. If the heater core is leaking is that where the coolant shows itself? Does it not go out the evaporator drain in the firewall?

The radiator cap should be releiving the system pressure if the head gasket is leaking and increasing the pressure in the system. Maybe you can monitor the level in the surge tank and look for bubbles.

Edit. The cap is no longer located on the radiator. The cap is now located on the surge tank and should be refered to as the "surge tank cap." The pressure relieving and vaccum breaker functions are located in the cap of the surge tank.

 

[Fless]

The radiator cap should be releiving the system pressure if the head gasket is leaking and increasing the pressure in the system. Maybe you can monitor the level in the surge tank and look for bubbles.

These radiators generally do not have caps.

 

[Donal]

These radiators generally do not have caps.

Yes, I should have been more clear in my post. The pressure regulating valve, vaccum breaking valve and fill function cap have been relocated to the surge tank. I will edit the earlier post to clarify. Thanks for catching the error.

 

[Big Mama]

Bone dry.

Good news and bad news. When you mentioned the coolant smell in the cab I thought that was it.

 

[Donal]

Bone dry.

Check the surge tank over flow/overpressure drain line. Look beneath the surge tank cap and see a small hose that goes down and along the front bottom of the surge tank. If the over pressure is venting, the hose should be damp or wet with coolant. That may be the source of the smell you detect occasionally.

 

[mattt]

Checked the surge tank overflow tube. Clean and dry underneath the surge tank and around the tube.

Is there anyone that has had a leaking heater core? How did you discover that it was leaking? Did it leak from anywhere?