2005 Tahoe Slow Coolant Loss

[Matahoe]

2005 Tahoe LT 5.3L, 220k miles, LM7. Slow coolant loss—no puddles, no drips, no sweet smell inside, no codes.

UV dye's been in 10k miles—black light shows no leaks anywhere, no clear streaks or trails. Perhaps I am missing something common? Water pump replaced at 150k by prev owner, thermostat at 195k by me, heads rebuilt. Still no change from before. Coolant still going down gradually.

Engine runs smooth and no overheat, but takes forever to warm up cold (possible rear HVAC valve removed when water pump changed?). No smell from HVAC, so front/rear cores probably not leaking.

Anyone seen this? Radiator weep? Pump seal? Thermostat housing? Or just evap from cap? Planning new rad this spring—want to pin it down first.

Thanks—pics if needed
Matt

 

[OR VietVet]

So...you never see drops on ground? Get warm and then shut off and no drops during hot soak? Have you ever pressure tested the system?

If the original heads were rebuilt and reused, may be the Castech heads coolant leak problems.

 

[Matahoe]

I had heads pressure tested to 4 x atm. Also developer dye crack inspected. No issues. No drips at all on the ground. Original heads were redone by me except the milling. Machinist said the heads were not warped. Just needed 7 thousandths milled. Not bad.

 

[Marky Dissod]

If the coolant cap is over 10 years old, feel free to just replace it already.
I get that no one likes to 'diagnose' by using the parts cannon, but I've no issue with firing the cheaper parts derringer.

If any smell is coming from the front, replacing the radiator may be wise. I've seen cracks too small for liquid to drip out still manage to leak by evaporation.
You said no drips on the ground. Did you check the rear right tire to see if coolant is dripping on it?

 

[OR VietVet]

@Marky Dissod reminded me of something. Have heard of slight seepage at radiator small cracks or seams and is small enough and hot enough that the wet is turned to very slight "smoke" and wet never hits the ground. Because of that likelihood of happening, I replaced my radiator even though I was not having coolant leak problems. I do check my rear heat connections, at right rear, on a regular basis.

 

[Scottydoggs]

heaqter hoses at the fire wall like to leak, its a very small leak

 

[Fless]

heaqter hoses at the fire wall like to leak, its a very small leak

Try fastening some paper towels around the heater tees, with tie wraps and run for a while. Remove them to see if they're leaking.

Engine runs smooth and no overheat, but takes forever to warm up cold (possible rear HVAC valve removed when water pump changed?).

I'm not aware of any HVAC valve -- can you elaborate?

Rent a cooling system pressure tester from your parts store and pressure test the cooling system.

 

[Matahoe]

If the coolant cap is over 10 years old, feel free to just replace it already.
I get that no one likes to 'diagnose' by using the parts cannon, but I've no issue with firing the cheaper parts derringer.

If any smell is coming from the front, replacing the radiator may be wise. I've seen cracks too small for liquid to drip out still manage to leak by evaporation.
You said no drips on the ground. Did you check the rear right tire to see if coolant is dripping on it?

Will check that. But as I said no drips on ground anywhere except a leaking rear main seal but that's oil. Cap, new factory reservoir and new hoses have only 30k on them. I don't notice any steam or strong smells anywhere. The radiator area does smell a tad like hot coolant when warmed up. Hmm. Now I am starting to think if I put dye in the coolant previously or not because the reservoir doesn't glow when a black light is held up to it. I do know the oil has dye in it by me. It glows.

 

[Matahoe]

Try fastening some paper towels around the heater tees, with tie wraps and run for a while. Remove them to see if they're leaking.




I'm not aware of any HVAC valve -- can you elaborate?

Rent a cooling system pressure tester from your parts store and pressure test the cooling system.

Nevermind I mentioned a valve if there isn't one. Just thought there might have been one previously. Just wondering if coolant is constantly being circulated in both front and rear HVAC evap coils. Will rent a pressure tester again. Might still be tough finding the culprit if test is positive. I could block off or connect feed and return hoses to the firewall for a bit. That might help isolate the issue.

I have some block tester blue fluid. Can try that again as well for blown head gasket. I checked it 4 years ago and there was no change in color.

 

[Fless]

Also, I'm not sure if your engine has front/rear steam vents (crossover tubes) but it's something to look into as you're pressure testing.

Loosing coolant. Underhood coolant smell

I was working under the hood today and noticed my coolant reservoir was halfway empty. It was fine a month ago when I added a few quarts. It was just below the line about 1/2 inch. I also have been smelling hot coolant around my radiator shroud/ front of engine area. I don't have any leaks on...

www.tahoeyukonforum.com

 

[TJ Baker]

My money is on the Castech head issue.

Be watchful for an intermittent smoke in the exhaust at startup.

 

[Matahoe]

My money is on the Castech head issue.

Be watchful for an intermittent smoke in the exhaust at startup.

No smoke in exhaust and mine aren't Castech heads.

"The Castech head issue in 5.3L GM Vortec engines (roughly 2001–2006) involves a manufacturing defect in 706 casting heads that causes cracking near the head bolt valley. This defect leads to significant, unexplained coolant loss, often resulting in sludge under the valve covers, a "milky" oil appearance, and sometimes misfires, typically requiring replacement of the heads."

I have none of this going on. Engine runs smooth, no misfires and no sludge. Here is a pic when I had the heads off. Heads are number 862 with no Castech logo. Which are identified by a small "battery" or "Castech" logo cast under the valve covers. Mine do not.

 

[West 1]

Put the radiator under pressure, 18 PSI is about as high as I am willing to test a system. Pump it up and watch, you may need to leave it for 24 hours and see if you lose any pressure. While pressurized you may find your leak. Sounds like it is a small leak.

GM sells tablets to plug micro leaks, they do work. I believe GM drops these in the engines when brand new just to avoid comebacks due to small micro leaks. They are cheap, available on Amazon, I think they come in a package of 5 tablets and depending on your cooling system size instructions will tell you how many to use. I think it tells you to drop them in with he system hot and then go for a drive of at least 30 minutes to distribute the tablets in the whole system.

I used them recently in an 2015 Audi A7 Turbo Diesel with a very slow leak that was hard to find. They worked perfectly in the Audi. I had already pressure tested the Audi, removed the Intake manifold and re sealed the Oil Cooler and EGR cooler, replaced the water pump and it still had the small leak until I added the GM tablets.

EDIT: I looked up the tablets from GM, $4 on Amazon. https://www.amazon.com/ACDelco-10-1...prefix=gm+coolant+leak+tablets,aps,178&sr=8-1

 

[Tonyrodz]

No smoke in exhaust and mine aren't Castech heads.

"The Castech head issue in 5.3L GM Vortec engines (roughly 2001–2006) involves a manufacturing defect in 706 casting heads that causes cracking near the head bolt valley. This defect leads to significant, unexplained coolant loss, often resulting in sludge under the valve covers, a "milky" oil appearance, and sometimes misfires, typically requiring replacement of the heads."

I have none of this going on. Engine runs smooth, no misfires and no sludge. Here is a pic when I had the heads off. Heads are number 862 with no Castech logo. Which are identified by a small "battery" or "Castech" logo cast under the valve covers. Mine do not.

View attachment 479230

I thought only the 4.8 had 862 heads. I had/have 2 vehicles that had 862 heads, and they both would get low on coolant, where I'd need to add coolant maybe once a month. They were an 05 Express van and my 03 Tahoe--which i swapped a 6.0 in. Imo it was the 862 heads. I never saw anything that pointed to coolant evaporating--sludge under cap etc, but later on the van was the oil pump was replaced and there was a ton of sludge in there.
I saw somewhere online that the 862 head also had Crack issues. I added those coolant tabs to the van and never had to add coolant again. Stayed that way for another 2-3 years until I sold it. The tabs are cheap enough to get and try. I think that'll solve your issue. Give it a shot, nothing to lose.
I used to change my oil every 3-3500k. Bought it with 110k. In these pics the van only had 144k on it. Imo it's from the coolant.

 

[TJ Baker]

No smoke in exhaust and mine aren't Castech heads.

"The Castech head issue in 5.3L GM Vortec engines (roughly 2001–2006) involves a manufacturing defect in 706 casting heads that causes cracking near the head bolt valley. This defect leads to significant, unexplained coolant loss, often resulting in sludge under the valve covers, a "milky" oil appearance, and sometimes misfires, typically requiring replacement of the heads."

I have none of this going on. Engine runs smooth, no misfires and no sludge. Here is a pic when I had the heads off. Heads are number 862 with no Castech logo. Which are identified by a small "battery" or "Castech" logo cast under the valve covers. Mine do not.

View attachment 479230

Good to know.

If this had been stated in response to post #2 I would not have brought it up.

I have the Castech heads AND I have had the issue going on 6 years now.

 

[OR VietVet]

Good to know.

If this had been stated in response to post #2 I would not have brought it up.

I have the Castech heads AND I have had the issue going on 6 years now.

I have repeatedly ran in to this concern. A member posts a problem but instead of posting ALL the concern info and repair attempts and testing results, in the original opening post, we get bits and pieces that come out as members here give info to try and help. If the OP is unaware of that initial info, I get it, but to then share the withheld info as a response to a HELP attempt, is mind numbing at times.

That, along with complete vehicle info, slows the process.

 

[Matahoe]

I have repeatedly ran in to this concern. A member posts a problem but instead of posting ALL the concern info and repair attempts and testing results, in the original opening post, we get bits and pieces that come out as members here give info to try and help. If the OP is unaware of that initial info, I get it, but to then share the withheld info as a response to a HELP attempt, is mind numbing at times.

That, along with complete vehicle info, slows the process.

Hey you guys are giving great info here! And sorry for any late coming specific info. Will try the tabs and see if that works. I put some CRC fiber lock block sealer in it around 2017. But that was before the head rebuild project. I have some left..but will try the tabs. Engine has 220k on it so I guess it's a science experiment at this point. Rear main seal needs replacement anyway. Thanks everyone!

 

[TJ Baker]

Hey you guys are giving great info here! And sorry for any late coming specific info. Will try the tabs and see if that works.

As I mentioned I have the Castech head trouble, confirmed on both sides with rocker covers removed. I have been using the tabs seemingly successfully now for 70,000 miles. I do occasionally have a flare-up, most often when the engine has been stressed going over some 12,000 foot mountain pass or when refreshing the coolant but for the most part I'm good.

 

[Matahoe]

I thought only the 4.8 had 862 heads?

Found this video a while back. Pretty cool info. I didn't realize the 862 heads were higher compression.

 

[Matahoe]

As I mentioned I have the Castech head trouble, confirmed on both sides with rocker covers removed. I have been using the tabs seemingly successfully now for 70,000 miles. I do occasionally have a flare-up, most often when the engine has been stressed going over some 12,000 foot mountain pass or when refreshing the coolant but for the most part I'm good.

Yeah. That higher stress means higher temps in the combustion chamber so any existing cracks in the coolant passages in the heads would widen. Makes sense. Likewise I notice coolant going down faster in the reservoir when downshifting / passing more often or in a hurry, etc.