Cooling SystemDear Ole Mechanic;

My pickup overheated about three days ago.  It is a 1992 Chevy half-ton with a V8 engine and an automatic transmission.  The truck overheated as I was going to a doctor's appointment.  I turned around, brought the truck back to town and caught a ride, so I could let the truck cool off.  When I got back, I checked the radiator and it took over two gallons to fill it.  There was a drip, drip, drip slow leak from behind the fan pulley--not enough of a leak to worry about unless I was headed out on a long trip.  Before I used the truck again, I topped off the radiator to make sure that it had plenty of water, but it didn’t took very little.  I didn’t get very far at all before the truck was steaming and showed overheating again, and there was even white smoke or steam coming out of the tailpipe.  What’s going on and what do I need to do?

Having a Hot Summer


Dear Hot Summer;

It sounds like your water pump is shot and leaking.  That's what caused your first overheating problem.  When the engine is running, the cooling system builds up pressure.  This is normal and that's why there is a warning not to remove the radiator cap when the engine is the least bit warmed up.  Unfortunately, that pressure can turn that slow drip of a leak that you saw from the water pump into a very large stream of leaking water.  The water pump needs to be replaced--but that's not all.

It sounds like when the truck overheated the first time, it may have gotten too hot on the way back to town and cracked something inside the engine.  Usually it is one or both of the heads that crack, but the block can also crack.  I say this because of the “white smoke or steam coming out of the tailpipe.”  A crack in the combustion area can do two things.  First, the combustion can force hot gases through the crack into the cooling system and increase the pressure.  This forces more water out of the water pump leak and can even force water out of the radiator cap.  Second, when there is a vacuum in the combustion area, water can be drawn in and turned into steam that you saw coming out of the tailpipe.  That takes water out of the cooling system too.  There is a way to check for cracks between the cooling system and the combustion area, but it will take a little mechanical work.  Remove the fan and water pump belt and also remove the upper radiator-hose and thermostat.  Fill the engine full of water through the thermostat opening.  When it is full, start the engine and let it idle while you look for bubbles coming up through the water in the thermostat opening.  If bubbles are present, then you have at least a blown head gasket, but more than likely a cracked head and/or block.  NO, radiator stop-leak will not correct any of these problems! 

The engine will need to be torn apart and checked for cracks and other damage.  I say other damage because too much heat can cause the piston and/or rings to weaken and fail.  It can also cause valve-guide seal failure.

Considering the age of your truck--fourteen years--probably the best option would be to either buy a rebuilt engine or to try to locate a used engine out of a wrecked truck.  Minimum cost for either of those options would be about $2,000 for parts and approximately the same for labor.  That should take care of the overheating problem but would still leave you with a fourteen-year-old transmission, suspension, rear axle, interior and paint job.

Most of the damage that you incurred could probably have been prevented by shutting down the truck at the first indication of an overheating problem.  In short, you probably did the most damage when you drove back to town after it overheated the first time.  There is a RED warning light or RED numbers on the temperature gage and RED means STOP!  I suspect that you are going to learn just how expensive it can be to ignore the RED  STOP indicator.  It is called a lesson from “the school of hard knocks.”

Herr Professor Nuzanbolts