Help! Where is 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

 

[bill81vette]

no signs of any leakage around the engine/hoses any where????
Its got to be going somewhere...

 

[Hib Halverson]

Your pressure testing...are you doing with the engine cold or at operating temperature? Also, have you run a pressure test immediately after noticing a coolant loss?

 

[boomdriver]

I'd guess that it IS leaking or using coolant whenever its running...just so slowly that its not measurable until a gallon down.
There is UV dye that can be added to a clean system and observed after some run time....The 87 has a couple great spots for small minor leaks. The junction of cooler hoses/heater hoses under the tensioner where the GM design team thought it a good idea to use a 2" section of hose to join two pipes....
The throttle body lines AND T-body lower gasket that holds water.

The cooler itself, the pipe, and even the heater core. You might want to get a tissue and press it into the passenger side carpet after one of these mystery losses and see if there is any unexplained moisture.

Worst case, water pump seal. Worser case...leaking head gasket or head bolts. If the heads have been off, I hope that the mechanic used thread sealer on the heads thru-bolts...if not, water will leak past the threads and vanish.
#7 holes head gasket area loves to leak. Common on L98 vettes.

 

[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!

vettebob

 

[boomdriver]

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!

vettebob

Thats an aluminum head.....mystery solved.

These heads won;t tolerate that kind of heat.

 

[FForward]

Intake leak?

Hi,
I had the same problem on my '89 and know exactly what your talking about. I couldn't find a leak either at that time and no problems overheating. Took me awhile to find my problem, but I did and its probably yours also. On top above the valve covers is a fat wiring harness that blocks the space between the cover and the runners for the intake. If you lift up that harness you can see down into where the intake meets the head. Its the same on both sides of the engine. Somewhere along the intake bolts you should see some discoloration or standing puddle of antifreeze. It could be anywhere along the intake on either side. My leak wasn't real bad, it was only slight sepage, so I only needed to add water once in several weeks of driving. My leak was close to the thermastat and at first I thought it was that leaking. I changed the gasket and sealed it up good, only to have the same condition back again. Later I needed to replace my injectors and as I was pulling off the wiring harness to move it away to get at the runner bolts, I saw the little puddle. I just went ahead and changed the intake gasket while it was torn down for the injectors. Problem solved! From what I understand about these engines its a common problem with leaky intakes. I guess form heating up and cooling down the gaskets don't hold up very good over time. I would suggest if your going to do the job yourself replacing the intake gasket, that you also replace the Multitech Injectors at the same time. That is if you have them. Jon at Fuel Injection Connecton has Boash Gen III's that will replace the junk injectors that Multitechs are. You will notice a big difference in the way the car runs. They are less than $300. for the set and well worth the money. Jon is great to deal with and is well known as the go to guy for injectors. Replacing the injectors now will save you a lot of trouble, money and time. Good luck! ....Bill

 

[ßill]

I'm going to go in another direction. Since you have pressure tested the system I would look for something not pressure tested: that 1/4 pipe from the pressure cap to the expansion tank. Does the expansion tank or line leak ? The level sensor is in the pressure tank near the firewall, no sensors in the expansion tank forward of the right front wheel.
Good Luck!

 

[vettebob]

Ok, thanks guys. I'll keep looking for the leak. I have a sneaky suspcion that I'm not going to find it until I rebuild the engine though, as there is virtually no evidence of an exterior leak that I can find.

Thanks again,
vettebob

 

[FForward]

Did you check around the intake where it meets the head, under that harness? These cars are prone to leaky intake gaskets. It only leaks a little bit, so you only have to replace the water every so often. Pressure testing won't find it and you won't see any signs of it anywhere. As stated above, I had the same problem and everyone said it was a leaky head gasket. I just kept adding water and driving it till my injectors went bad. When replacing those, that wiring harness was moved out of the way, and thats when I spotted where the leak was. You cannot see down in there untill you move that harness. If the car sat for awhile it would disapate and only a discoloration could be seen. Drive the car around and then check the intake, you should see fresh antifreeze somewhere coming out from the intake gasket between the head and intake. Have you done that? I am so sure this is your problem! Being a mechanic, you should already know that if it was a head gasket, there would be white smoke coming from the exhaust. If its not leaking on the ground and there are no signs of any leaks anywhere, your problem is the intake gasket. A leak there will not show up on the ground and its sits there on the intake. There is not a big enough leak there that would cause it to spill on the ground. Good luck!.....Bill

 

[vettebob]

Ok, I'll have a good look there and see. Thanks!

I've been wanting to put a cam in this car, but if I am going that far I should go ahead and rebuild the engine. If I am going to have to pull the intake, well, I'll probably find myself into a full blown overhaul as I won't want to pull the intake again later.

Thanks,
vettebob