Car is overheating; what are the possible causes?

Factual Questions
1

OK, mechanically-inclined Dopers, here’s the situation:

I have a 1989 Dodge Dynasty with a 6-cylinder engine, automatic tranny.

The engine temp gauge on my dash keeps indicating that the car is overheating (this began yesterday).

I’m not leaking antifreeze anywhere that I can see.

There is no steam or hissing noises coming from any part of the engine.

I just replaced the thermostat yesterday, thinking that it might have been the problem, but I still get the same symptoms. When I replaced the tehrmostat, I had a loose bolt on the housing connecting the radiator hose to the manifold, and when it overheated this time there was steam, but only from the area that had the loose bolt. This however did not happen before I replaced the thermostat.

I checked the oil level, which was normal. I’m thinking that if I had a cracked engine block that I would probably have oil mixing with antifreeze and raising the oil levels, but there was nothing abnormal there. (I’m not sure that is a reliable indicator, though.)

The antifreeze reservoir seems to be overfilled now (it wasn’t before).

So, is there anything else I can check or replace before I give in and take it to a garage?

2

On a car that old, it could be that the radiator is getting clogged. Have you been flushing the cooling system at regular intervals over the last several years?

Could also be that your water pump is failing or you have a loose belt running the water pump. If the pump is failing or the belt is loose, you should be able to hear something is wrong. The bad pump usually makes bad mechanical sounds though not always and a loose belt should squeal.

When the car is cool, open the radiator cap, start the car and wait for it warm up. When the thermostat opens, you should see lots flow through the radiator, telling you that the thermostat is working and the water pump is pumping.

I’m not sure what happens if the the cap is off and the radiator is clogged.

Good luck

3

One other thing, if the car is over heating but the heater in the car is not as warm as usual, you can reason that the water pump isn’t pumping as the heater has nothing to do with either the radiator or the thermostat.

I believe the heater core runs on the same loop as the engine block so that even with the thermostat closed, the heater core should be getting warm water from the engine block. At least that is the way it was on my old VW golf.

4

Does your radiator cap look like it is sealing well? Check the rubber seal, and the spring.

The overflow into the resorvior suggests overheating. But it may just be that the seal on the radiator cap is bad.

If your cap isn’t sealing, it may cause overheating and some of the steam is getting buy to the overflow.

Any strange smells, humidity, inside the car when the heat is on. That would suggest a heater core problem.

Just an idea.

Also billy had some very good ideas.

Good luck.

5

Thanks for the replies.

I’m not getting much (if any) warm air from the heater in the car, and when I turn on the heater there is a bit of an odd sound to it.

I have not had a radiator flush and fill done in quite a while. If there is a clog somewhere, will a flush and fill clear it out?

6

It is possible that the heater is cool because it is also clogged but that shouldn’t cause overheating of the engine. The odds of both the radiator and heater core clogging at the same time seem rather low. It sounds most likely that your waterpump isn’t working.

I do not know if flushing a radiator will unclog it.

7

Long shot: Did you check the new thermostat before you put it in and did you check the old one when you took it out? (Put it on the stove in water with a thermometer and watc for it to open when it reaches the correct temp).

I have bought brand-new defective thermostats.

I imagine the others are more likely correct, but it’s something to ponder…

8

Does the radiator have holes in it? Also, there are tests dye tests you can get at the auto store to test for oil in the radiator water, which, as mentioned above, needs to be changed at least every two years depending on what the car manf says.

9

Aside from problems that are directly related to the cooling system, other things that can cause overheating are dragging or sticking brakes, and running too lean. If the car overheats while sitting still, you can safely ignore brakes. :smiley:

Combining the symptoms of the engine overheating and little heat from the heater seem to add up to either a plugged heater core, or more likely, tired, if not dead, water pump.

Probably the best thing to do is take the car to a radiator & cooling system shop and have them check it out. Don’t be surprised if you need a new radiator and/or heater core - I’ve seen seemingly healthy radiators spring leaks after a cooling system flush - the gunk that was sealing up corroded-out holes is cleaned out, leaving holes. :eek:

10

While your heater post would suggest otherwise, it is possible that your overheating is caused by a bad electric fan, fan relay, loose wiring or defective thermo switch or ECT sensor (the switch or sensor that tells the fan to come on).

Any underhood source of 12V can be used to test the fan’s motor.

A multimeter or test light can fill you in on the rest- the fan should energize before the car “overheats”.