Coolant loss with no external leak

Has anyone experienced coolant loss without external leaks? We have a 2001 Tahoe with a Vortec 5300 engine. We have 85,000 miles.

Mine does that a bit. It gets just low enough in the overflow tank to throw on the low coolant light on the dash. Mine happens probably every few months. I haven't seen coolant on the ground anywhere though. I put a bottle of stop-leak in the radiator to see if it would stop it. Helped for a while and then it did it again. I'm stumped as well.

If it was a bad head gasket, wouldn't you see some evidence of it in the oil?

^^^It's MOST likely NOT going into the oil but leaking very slowly into the cylinders.

Big Tap said:

If it was a bad head gasket, wouldn't you see some evidence of it in the oil?

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Most of the time if you see anti-freeze in the oil, its REALLY bad. Most small headgasket leaks do leave some anti-freeze in oil. But only way to find these is through oil analysis. I have had hundred's of blown head gaskets through the doors and I can only count on 1 hand the number of times I saw anti-freeze in the oil. Like I said above if its that bad, you know something is broken.

John

Watch for excessive moisture on exhaust tips, some is normal depending on temp and how often you drive. If your oil is muddy, you have real trouble. Intake gaskets are common to leak on these, pain to change but possible if you have tools and time. Good luck on this.

Mine started doing the same thing around 90K miles. Took me a while, but I finally found that it was coming from the rear of the intake gasket. It only started to leak once the engine was at normal operating temp, enough for pressure to build up and push it out the bad spot on the gasket. And even then, it's barely enough to cause it to run down the block enough to drip, making it harder to find. I have to refill the overflow tank about every other month.

Your best bet to have the coolant system pressure tested. This test should be performed on a cold engine and then when the engine is up to operating temperature.

Doing this pressure test will most certainly let you know where your leak/leaks are.

Sepiroth said:

Your best bet to have the coolant system pressure tested. This test should be performed on a cold engine and then when the engine is up to operating temperature.

Doing this pressure test will most certainly let you know where your leak/leaks are.

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X2

Pressure testing the coolant system may reveal a leak or may not, these tahoes and trucks with the 4.8, 5.3, 6.0 V8's have a bad habit of leaking heads causing coolant to enter the oil system and sometimes burn it thru the cylinders. Pull your oil fill cap and see if there is a lot of condensation on the underside of the cap, or if there is sludge under there, also if you have coolant leaking into your oil, your oil level will be high. Another way to indentify what may likely be happening is whats called a block test, usually done by a professional, it determines if there is carbon monoxide entering the coolant system, as we all know, carbon monoxide aka CO is a poisonous gas emitted from our tailpipe. Some of these vehicles have "Castec" heads, they can be indentified by the stamping number near the oil fill tube right next to the rocker cover gasket, I don't recall what the culprit number is right now, but if you check your casting number (usually 3 characters), I will check it to see if you have castec heads. Good luck!

P.S. not trying to call out avdoc, but these vehicles have "dry" intakes, not "wet" intakes like back in the good oil "R" motor days, so, leaking intake gaskets would NOT cause any coolant in the oil or any coolant loss at all, but rather a lean condition and usually sets off the SES light when cold startup

I have a 2000 Suburban 5.3 W/head coolent leak Fixed!!!

I have a 2000 Suburban with a 5.3. I started loosing coolant little bits at a time. I would have to top it off every month or so. It finally started getting worse. As it got worse my engine oil started to really sludge badly. The oil color was normal to dark. It never got milky. It started tapping on startup till it got warmed up. I started changing my oil more frequently (normally I would change it every 3k). My last oil change was mostly sludge. Even the filter was clogged with sludge. I did some research and found out about the bad lot of cast aluminum heads. (Chevy has a TSB out on them)
Since I could never find where the coolant was leaking combined with the oil sludge it was obvious where my problem was. To delay the head replacement I used Bars Leaks in the coolant. That was about 3 months ago. I have not lost any coolant since. I will update the next time I change my oil. The Bars Leaks is holding for now!!!

I went through this and it turned out to be two cracked heads. The only problems I saw was when I started it up it would blow blue smoke out the tail pipe, and it smelled like gas not burning. Of course it didn't do it all the time. I had to take it in several times before they believed I was not crazy. Lucky for me I had an extended warranty on it so it only costed me $100 bucks.

gm makes special coolant sealing tablets that may help. they are made of, believe it or not, crushed walnut shells. check with you dealer, they should have in their parts dept. the fibers from the walnut shell materials go into suspension in the coolant then act to form a "plug" at the site of the leak. sounds weird, but there you go.

IMHO, that's like putting a band aid on a cut that requires stitches!

Sepiroth said:

IMHO, that's like putting a band aid on a cut that requires stitches!

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well, you know the saying about "opinions".

is standard s.o.p. to put these into some gm engines as a matter of routine when they were 1. built, and 2. when a coolant change it done.

is cheap, easy to do, and if it solves the problem, you save huge $.

Yea, but why should you have to do this step? It would be obvious to me that there is some sort of issue that negated this call. Perhaps another way for a mfg to cheap out on warranty claims.

i am having the same exact problem airframe is having or did have i thaught the sludge was from switch from valvoline to castrol so i switched back to valvaline and the sludge is not as bad but its still there i just changed my oil agian with valvoline so i will see if i am still haveing sludge problems but yeah i have the ticking at start up capichino under the oil fill cap no visible signs in the oil so what is it i see he used the head gasket repair stuff maybe i will try that to see if it helps

Sepiroth said:

Yea, but why should you have to do this step? It would be obvious to me that there is some sort of issue that negated this call. Perhaps another way for a mfg to cheap out on warranty claims.

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i am in complete agreement with you. you should not have to do this. from what i read, some of the aluminum block engines gm built had too much "porosity" and they had to use this treatment to completely seal the internals off from oil seepage. go figure. but, it seems that is also worked well to seal off realtively "minor" leakage problems also. just passed that on in case someone wanted to give it a whirl to see if would help their problem. if i find the article on it, i will post it for anyone interested.

P.S. not trying to call anyone out, but these vehicles have "dry" intakes, not "wet" intakes like back in the good oil "R" motor days, so, leaking intake gaskets would NOT cause any coolant in the oil or any coolant loss at all, but rather a lean condition and usually sets off the SES light when cold startup