Questions and Answers

Overheating??

Q. I have a 1989 Olds 88 Royale. Automatic 6-cylinder with 222,000 miles. A/C, fuel injection, cruise, Power steering windows & locks.

This weekend, while driving on the highway, my engine temp light came on for a couple of miles, then went out. I stopped 20 miles later and got some gas. I popped the hood, the engine did not seem unusually hot. I got back on the highway and after 2-3 miles, the temp light came on and stayed on. I turned around and went back to the gas station. When I popped the hood this time, coolant was overflowing the Overflow tank and had been for some time, because there was coolant all over the place. This was the first time ever, that I've seen the temp light. No previous problems with radiator. I had it flushed just 3 months ago (but it had been about 40000 miles since the last time.)

Got the car towed to a shop that usually does good work. They replaced the water pump and mentioned that the radiator looked bad. I picked up the car and drove the three miles back to work. I popped the hood and checked the radiator cap -- it was not hot. There was no coolant in the overflow tank. I took off the cap. Coolant erupted like a volcano and some splashed on me. It was NOT hot. Almost all the coolant came out. I got a galloon of coolant and filled it up. On the way home (3 miles) the temp light came back on.

What could be the problem?

Thanks,
Matt

A. Well Matt, two things come to mind here, a thermostat stuck closed or an air bubble in the cooling system.

The thermostat is easy and cheap enough to replace, so we can eliminate that possibility easy enough.

Getting rid of an air bubble can be a little tricky. Some engines have a cooling system air bleed that you can open while you fill the system. You can disconnect one of the hoses to the heater core to bleed the air out, but personally I don't like that method. The hoses get stuck to the heater core tubes pretty good and there's a real chance of breaking one.

What I do is kind of take advantage of a little science. First I move the heater temperature selector to full hot. Then I fill the cooling system with as much coolant as possible and overfill the reserve tank by half. I put the cap on and start the engine. As the engine heats up you will see air bubbles in the reserve tank. That's the air from the cooling system heating up, expanding and coming out of the reserve hose. After about 30 minutes of running, turn the engine off, go in the house and find a game on TV to watch. As the engine cools down, it will draw coolant from the reserve tank into the cooling system to replace the air that was forced out.

Keep an eye on it as it's running, if it starts to overheat, just shut the engine off and let it cool down. As it cools, it will take coolant from the reserve tank. After it cools down, refill the reserve tank and keep an eye on it for a few days. Make sure the temperature lever is on full hot. This will get about 90% of the air out of the system and the rest will bleed out as you drive.