Where's my water going???

[vettebob]

1987 Corvette.

Been a mechanic for 40 years, but I am having trouble with this one.

My Corvette will hold a 17 lb. radiator pressure test for hours without dropping even 1/2 lb. and not a drop of water leaks out anywhere.

However, the car may run fine and hold water for weeks, and make long desert trips without overheating nor losing water. But every once and a while the low coolant light will come on, and I find the car anywhere from a quart to a gallon low on water.

It is on it's second new radiator cap, the overflow tank never gets too full, cooling system has been flushed and tested, it has a new 180 thermostat, etc. and as I said, with 17 lbs. of pressure on the cooling system it sat on concrete for several hours without a single drop of water leaking out.

Where and how the hell is it losing water sometimes??

Thanks,
vettebob

[LLC5]

Originally Posted by vettebob

1987 Corvette.

Been a mechanic for 40 years, but I am having trouble with this one.

My Corvette will hold a 17 lb. radiator pressure test for hours without dropping even 1/2 lb. and not a drop of water leaks out anywhere.

However, the car may run fine and hold water for weeks, and make long desert trips without overheating nor losing water. But every once and a while the low coolant light will come on, and I find the car anywhere from a quart to a gallon low on water.

It is on it's second new radiator cap, the overflow tank never gets too full, cooling system has been flushed and tested, it has a new 180 thermostat, etc. and as I said, with 17 lbs. of pressure on the cooling system it sat on concrete for several hours without a single drop of water leaking out.

Where and how the hell is it losing water sometimes??

Thanks,
vettebob

With no visual leaks externally, then head gasket or heater core come to mind.

[Ed89]

I have an '89 and have a similar problem with the Low Coolant light. If your loosing Coolant it could be the manifold intake gasket, I found a little pool of Anti-Freeze on top of my engine. The position of the Low Coolant sensor leads it self to a low coolant indication. I was tolled to open the radiator cap and have someone rev the engine until the thermostat opens and the water starts to reseed from the filler cap, at that point top off and close the cap. This is an annoying little problem I still get now and then.

[vettebob]

I don't think the heads have ever been off of this one. I replaced all the water hoses, and I've been all over the front end of the engine removing the smog equipment, replacing the a/c compressor, etc. I replaced the water hoses down for the oil cooler down near the exhaust/oil filter with high quality braided hoses. I can't see any staining or dripping anywhere. Usually you can smell a heater core leak inside the car and/or see steam on the windows sometimes, and I don't experience any of that.

Right before I bought the car it was run low on water and got up to about 300 degrees. I was there at the time and made sure no water was added to the engine until it had thoroughly cooled down, and even then made them add water slowly and with the engine running. I'm worried that maybe it has a cracked head that only leaks when thoroughly warm and running. But I have made 7 hour trips across the Mojave desert with the car with no water loss and no overheating so that doesn't make much sense either....

I forgot to mention... Plugs look normal, a little cleaner on one side than the other because it is leaking a bit of oil down the valve guides, but they all look the same. (Need to install the valve guide seal fix.) Also, no signs of oil in the water or vice versa. Car has 96,000 miles. Sometimes it will hold water for weeks, sometimes I have to add water twice in one week!

When I add water, I do rev the engine in order to get it completely full of water as you mentioned.

vettebob

[LLC5]

Originally Posted by vettebob

I don't think the heads have ever been off of this one. I replaced all the water hoses, and I've been all over the front end of the engine removing the smog equipment, replacing the a/c compressor, etc. I replaced the water hoses down for the oil cooler down near the exhaust/oil filter with high quality braided hoses. I can't see any staining or dripping anywhere. Usually you can smell a heater core leak inside the car and/or see steam on the windows sometimes, and I don't experience any of that.

Right before I bought the car it was run low on water and got up to about 300 degrees. I was there at the time and made sure no water was added to the engine until it had thoroughly cooled down, and even then made them add water slowly and with the engine running. I'm worried that maybe it has a cracked head that only leaks when thoroughly warm and running. But I have made 7 hour trips across the Mojave desert with the car with no water loss and no overheating so that doesn't make much sense either....

I forgot to mention... Plugs look normal, a little cleaner on one side than the other because it is leaking a bit of oil down the valve guides, but they all look the same. (Need to install the valve guide seal fix.) Also, no signs of oil in the water or vice versa. Car has 96,000 miles. Sometimes it will hold water for weeks, sometimes I have to add water twice in one week!

When I add water, I do rev the engine in order to get it completely full of water as you mentioned.

vettebob

If you cannot find any external leaks, then you may want to consider doing a cylinder leak down test with the engine hot and the radiator cap off with the coolant level filled to the top of the cap area (which would be overfilled to the very top of the neck). Look for any bubbles coming up through the coolant in the radiator, remembering that the coolant level has to be up over the top of the neck to see any bubbles if there are any. Good luck with it.

[ChuckG]

I'd send the oil out for analysis before I dug into any really heavy work. It's a nice guide.

[vettebob]

Ok, thanks guys. I'll keep looking.

vettebob