Overheating Problem 95 Geo Metro

[Too Many Old Cars]

My 95 Metro has begun overheating. I've replaced the thermostat without effect. My radiator was leaking a few years ago and I used a chemical sealant. Thought maybe the radiator was plugged so I pulled an almost new one from the junkyard. No change. Recently the water pump began leaking. I replaced the water pump and put in a new timing belt at the same time. It still overheats. I'm at a complete loss as to what can be the problem. The coolant seems to be flowing okay and I get a hot intake hose as well as exit hose from the radiator. I can drive for short trips okay but after about 15 minutes it will overheat and the coolant boils out. Any suggestions as to what I should check?

[Woodie83]

Thermostat is the first thing you should check. My experience with sealers is that you'll be replacing everything about two years after you use them.

[Crvett69]

make sure the radiator fan is coming on. once car is up to operating temp you can also feel across the middle of radiator with fan off and make sure its hot all the way across, not just hot on the outer tubes and cool in the middle. depending when you changed the thermostat you may need to replace it again. you can always pull it out and see if it still overheats

[Too Many Old Cars]

The previous thermostat was about two years old. I pulled it and put it in a pot of water on the stove. It opened just as the water began to boil. It looks like it is still good but was set to open at 190 degrees and so I bought a new one that opens at 165 degrees and put it in about three weeks ago.

The fan is coming on but I'm not sure at what temperature it turns on. How can I test that? The car heats up so fast, however, that I suspect the coolant isn't getting through the system properly. I had not thought of feeling the radiator to make sure fluid is flowing through the entire thing properly. I'll test that tonight to see what I find.

[redpepe]

hi tmoc,

not sure what your initial problem is but maybe try simply removing the tstat for a while. this will help to tell you if the rest of the system is working properly since it will necessarily be at maximum cooling ability. take the car to a steep long hill on a hot day and watch the performance. run the ac too if you have it. with the fan on / cycling, the system should be able to maintain a steady mid range under any load.

the engine controls are set up for a specified range of operation and changing the tstat temperature will have systemic consequences which will be hard to predict or account. imho, the factory designed and balanced the components very well and terrific mileage and longevity are the result. i recommend the oem tstat but i even had to replace a new one of those because it was not calibrated / performing within the original range.

harbor freight sells an ir thermometer for about $26 on sale. they are quite accurate in my limited experience and you can easily get temperatures from many spots on the engine and cooling system.

[Too Many Old Cars]

Issue Resolved

I thought I'd post an update since my Metro overheating issue is finally resolved. I don't recall the brand of radiator sealant I used but it has left a black waxy-greasy residue throughout my cooling system. My best guess is that my water pump began to have problems at that point--probably because of the sealant. Although water pumps typically leak when they go out, I think the sealant kept the water pump from leaking until a few weeks ago. When I replaced the pump it fixed the problem but I didn't realize I had fixed the problem because I filled up the radiator after I replaced the pump and didn't check for an air bubble (duh). After the engine ran for a while and overheated again. I assumed there was another problem. When I found the coolant level had fallen I added another quart of coolant and that took care of the problem.

[Woodie83]

You sure it's not engine oil?

Bad head gasket will do the symptoms you describe. Sometimes with oil in the water, sometimes with water in the oil, sometimes with neither.