Dear Tom and Ray:

I have a 1993 Toyota pickup truck, a 4-cylinder base model. It keeps overheating. Usually it happens in the morning and on the way home. Once it is running awhile, it seems to run at a normal temperature, according to the gauge. I had the thermostat replaced twice and the water pump replaced. I had the system flushed and refilled twice. Nobody knows what it is. This is a great truck, with 200,000 miles on it. The mechanic at the shop wants to buy it from me since it has almost no rust on the frame or elsewhere. I'm grasping at straws. Could it be some type of sensor? I get lots of hot heat in the cabin when it's overheating. What do you suggest I do next?

-- Mel

TOM: When you take it back to your mechanic again, Mel, write "For Sale" on the windshield.

RAY: Actually, since you're obviously attached to this truck, I'm going to recommend some exploratory surgery.

TOM: My guess is that you have either a bad head gasket or a cracked head.

RAY: Having a cracked head is far worse. I mean, look at my brother.

TOM: What's happening is that right after you start the car -- in the morning or in the evening -- the very hot exhaust gases created inside the cylinders are getting through a breach in the cylinder head gasket or the cylinder head, and they're getting into the water jacket (the passages inside the cylinder head that carry the coolant).

RAY: Once those exhaust gases -- which are several hundred degrees Fahrenheit -- mix with the coolant, they heat the absolute bejeebers out of it.

TOM: It's possible that once the whole engine gets hot, things expand and the hole in the head gasket or the crack in the cylinder head closes up. That allows the cooling system to catch up and get the engine back down to normal temperature -- until the next time you start the cold engine.

RAY: But eventually, that breach will get bigger and it won't close up at all, and your truck will overheat all the time. And then you'll warp the head and fry the main bearings, and even your mechanic won't want to buy the truck from you then. So you need to fix this, Mel.

TOM: If the truck is mechanically sound, other than the overheating (a question your mechanic should help you answer on a 20-plus-year-old truck with 200,000 miles), then I'd pay your guy 300-400 bucks to remove the head and see what's going on.

RAY: Once the head is off, he might see a clear breach in the head gasket. That'd be the best-case scenario, and I'd say there's an 80 percent chance that that's what he'll find. Then he cleans up the head, replaces the head gasket, puts the engine back together, charges you $1,000 for the whole job and sends you on your merry way.

TOM: If he doesn't see a tear in the gasket, then it's likely that your head is cracked. At that point, you'll have three options.

RAY: Option one is to buy a used head. Then the whole job will run you about $1,500, since there's a lot of work to be done prepping a used head for installation.

TOM: Option two is to buy a used engine. Believe it or not, that would cost about the same. You've already disconnected most of the stuff to pull off the head. And it's such a simple job on this truck that even after you pay a few hundred bucks for a used engine, you'll still get out for about $1,500, maybe a little less.

RAY: And if you go that route, you'd also be smart to replace the clutch while the engine is removed. The extra labor at that point is trivial, and for a few hundred bucks more, you'll walk away with a brand-new clutch, too.

TOM: Option three is to turn to the mechanic and say, "Hey Frank, any chance you still want to buy this?"

RAY: So see if it's the head gasket. If it's not, I'd put a used engine in it. Then you'll be stylin', Mel.