1999 5.3L Losing Coolant

[estone4009]

I have a 1999 Silverado 4wd that is loosing coolant. After 3 or 4 days of regular driving you have to fill the surge tank back up. I have had the cooling system pressure tested, coolant replaced and thermostat replaced. I have had a chemical test done on the coolant to see if there was a head gasket problem. There are no visible leaks on exterior of any parts. All test have shown nothing. The oil does NOT have coolant in it. The only other place I'm being told ot that it is making it to the exhaust and disappearing as steam. Could that happen through the intake manifold or a crack in the head/s? I'm open to any remote ideas at this point.

[jeverett]

I have just recently had this exact same problem on my 99 Z71 w 5.3. I had all of the same tests performed that you described, and like you, didnt show a thing. I had heard mention of maybe a faulty intake gasket being the problem. I took it to my mechanic, who after ordering the intake gasket set, took the intake off and the old ones were pefect. I just told him to fix it, so he went a step farther and took the heads off. On the passenger side head gasket was a VERY small hairline crack. I didn't think a crack that small could possibly loose that much water that fast, but it did. My oil didn't have any water in it for a while, but after a month or so, it finally showed up and it was pure hell to get it all out of the engine after I had it fixed. I can give you one more test that the GM shop manager gave me. Park your truck overnight on a dry level surface. Next morning, slide a large piece of cardboard under the engine compartment and start the truck up. It could possibly be an external leak that is too small to be seen by eye.

I hope this helps ya, becuz unfortunatly a month and $500 later, I can sympathise with you on this.

[estone4009]

Does anyone know if it would be wise to try some of that coolant leak fix to see if I can get it to stop leaking? Or will that stuff do more harm than good?

[john877]

i wouldn't recommend a leak stop, sometimes they can clog up legit passages through the engine. have you tried to pressure checked each of the cylinders? also, I had a difficult time with hose clamps. replaced all my hoses at 100k and replaced clamps with the worm still clamps. I must have tightened those things at least two dozen times over six months before they would stop leaking. i would make sure all hose connections are tight.

[estone4009]

I checked all the plugs today and they all appeared normal. I also pressure tested all cylinders and they all looked fine with no considerable difference between them. If the coolant is going out the exhaust in small amounts is there any way to test or catch that. There is some amount of steam out the exhaust but I couldn't say exactly how much because of the outside temp. Or am I better off to take it to a shop and let them tear the heads off and inspect each one for hairline cracks?

Thanks

[john877]

Well, the steam in the exhaust is not good. Now, I'm assuming this is steam after everything is warmed up to operating temp and run for say 10-20 miles. You may be looking at something as simple as a head gasket leaking coolant into the exhaust or something as major as a cracked head. Either way it's problem that needs to go to the shop and have the heads removed to check for a gasket leak, once they are removed they may be able to pin point problem. Hopefully, there will to be no crack and a visable sign of a head gasket problem. I would definately get it into the shop.