Dear Tom and Ray:

I have a 1982 Chevy pick up with a 305-V8 and 128,000 miles on it. Recently, I've had to add coolant to my radiator every few days. It's not leaking onto the ground. I can't find any leaks from hoses or clamps, even when the engine is hot and under pressure. There's also no sign of water in my oil when I change it. Where can I be losing it? The engine block? The heater core? The left rear tire?
Gary

TOM: Oooh! You were so close when you guessed the left rear tire, Gary. Where you're losing it is out the tailpipe.

RAY: You have either a blown head gasket or a cracked head. The coolant is leaking into one or more of the cylinders, and it's being vaporized during combustion along with the gasoline. Then the vapors are going out the tailpipe. Haven't you noticed those voluminous clouds of white "smoke" that come out your tailpipe first thing in the morning? That's coolant vapor!

TOM: Here's how you test this theory. Have your mechanic hook up the cooling system to a pressure tester, and leave it pressurized overnight. The next morning, remove the spark plugs and turn the key to start the engine. If one of your cylinder heads or head gaskets are leaking, coolant will come shooting out of at least one of the spark plug holes.

RAY: I usually tell my brother to lean over and look inside the cylinder before I try starting the car, but that's just for yuks, it's not a necessary part of the test.

TOM: If it's your head gasket, Chuck, it'll cost a few hundred dollars to replace. If your head is cracked, I'd suggest you visit a junkyard and look for a used cylinder head. Just be careful not to leave your truck unattended for too long. They may mistake it for something that escaped from the yard.