What's Going On Here?

[jgmotto]

OK, this is driving me a bit nuts. I've driven my '89 for 14 years and thought I've seen it all. Just turned 200,000 miles and the car has been great. Other than normal maintenance stuff (which I do mostly myself), never had any serious problems. The engine has never been opened up. So here's the deal. About 3 weeks ago, I had a "Low Coolant" light come on. I did a pressure check on the radiator and found a pinhole in a heater hose, which I promptly fixed. I pressure checked again and it held fine. Over the following days, the warning light came on a few times after and I thought that I just had air trapped, so I did all the tricks to get the system full. After days and days of refilling and trying every trick in the book, I realized that the coolant was going somewhere. No visable leaks. The weird thing is that it seems like the system is getting air in but it never draws any fluid back from the overflow tank. In fact, if I force fill it, the "Low Coolant" light comes on and the overflow tank overfills and spills. OK, logic says that the head gasket is leaking and pressurizing the system with gases. No water in the oil. It runs fine, except for a faultering idle just once and awhile (mild and not unusual). So I spent all day today doing a compression check. All cylinders measured between 155 to 165 psi. Differentials between adjacent cylinders did not exceed 5 psi. So why am I having this problem? Can air be pumped into the cooling system any other way? Can a small pinhole leak or crack cause this but not show up on the compression test? Other than tearing the engine down, how else can I troubleshoot it?

 

[WhalePirot]

RU getting extra water in the exhaust?

Are your plugs rusty?

 

[jgmotto]

Haven't seen any evidence of water coming out the exhaust. The plugs look pretty good. Some minor black soot but pretty clean overall.

 

[Tuna]

What kind of oil are you using?
Synthetics don't turn to chocolate milk nearly as fast as regular oils do so it can be deceiving.
Check the dip stick both hot and cold - do you see small bubbles in the oil on the dip stick?
If the leak is heat related, let it warm up good and then check the exhaust pipes with it running for water or steam coming out. Should not see any water/steam once the motor and pipes are warmed up.
Okay, that's my comments for troubling shooting a head gasket problem.

I'm sure you've already checked all the hose clamps to make sure they are tight. I had one loose on my Buick a while back that didn't leak until it got hot.

Good luck with your trouble shooting.

 

[jgmotto]

Thanks for the reply, Tuna. I'm running Mobile 1. I went out and checked it with the engine hot and I don't see any moisture coming out the exhaust. The oil on the dipstick looks clean without bubbles.

 

[vetteboy86]

I know someone Vettefan87 who had a low coolant light come on, and he did
everything to find out where it was going. However one day we checked the oil and saw milk chocolate on the dipstick. Keep close tabs on the problem.:confused

Good Luck

Craig

 

[jmccloud]

Lost coolant

You got a bad radiator cap.

Sounds crazy but I suffered the same sypmtoms for 2 or 3 months. One day while looking at the water pump, etc. my wife walks out and asks, "Is water supposed to coming out of there?" She was point to the back side of the pressure cap where I never looked. (up until then)
New cap, no 'loss' of fluid into the reservoir, and the radiator stayed full, no more 'low coolant' message.
Hope it's that easy for you.
She still reminds me of it daily.

 

[drags1998]

I found that one MUST add the G.M. gold stop leak pellets (3) to the cooling system ANYTIME you have to add a bunch of coolant!!!!! It has always worked for me!!!!!

 

[jgmotto]

I'm not familiar with G.M. gold stop pellets, drags. What are they and where do you get them. I just did another pressure test on the radiator just to be sure I wasn't missing a leak somewhere. When I pumped it up to 16 psi, it dropped ever so slowly about a half psi every 10 minutes. Then I tried running the engine up to operating temp with the pressure gauge still on. The pressure didn't rise quickly which I take to mean there isn't a serious head gasket leak. But when I pumped the pressure up a little more, steam came out the exhaust pipes. I'm beginning to be convinced that it is a very small head gasket leak into the combustion chamber. I'd like to try a radiator sealer but one that won't gunk up the system. I had a bad experience once with Bars Leak black pellets. Any suggestions on one that works better?

 

[jmccloud]

Pellets

A chevy dealer will have the pellets. They're $6 or 8 for a packet of 3.
They're a must use.

 

[drags1998]

The G.M. part# is 12378254 . I have found these to be the best I have ever used and they DONT crap up the cooling system!!!!!! 3-4 will do the trick, Just go for a good ride after installing them. Good Luck, Paul

 

[redc4corvette]

Did you check your intake gasket vette always have small intake leaks that go undetected .Just might need an intake gasket if the EGR valve burned throuth?