98 sohc overheating 105K miles

The check gage light came on today after a short trip and when I looked my temp gage was pegged at the high end. I pulled over and turned on the heater on high and the temp dropped down enough to turn the trouble light off and drive home on.

I just recently moved back from a warm climate and have been driving and parking outside (Chicago) in very cold temps for the first time in years.

I pulled in it in the heated garage to let everything thaw for a few hours and then started it and let it idle and it went back to the high end after about 15-20 minutes.

Coolant reservoir is at the proper level. When I turn on the heater it heats up and blows hot air and the engine temp drops so that tells me that the waterpump is at least providing flow. At the same time the top radiator hose is warm but not as hot as I would expect.

This all leads me to believe that the thermostat is stuck.

My repair manual is packed up in some warehouse right now so I can't check it. Do all of these indications make sense for a stuck thermostat? How hard is it to replace on this car (I've done them on several other cars).

I also did a google search and found a thread that recommended using only original for thermostats due to a better design for this model. Anyone else know about this.

As always thanks in advance for any help,

Steve

Reply to
sehaare
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One other important thing that I forgot to mention: The Fan does run but it starts running as soon as the car starts. Is that normal?

Thanks Again Steve

Reply to
sehaare

The fan will run if the AC is enabled.... the AC is enabled if air blows on glass....

First thing is to check the strength of the coolant.

Reply to
Jim Warman

Jim,

I flushed the system and replaced the coolant less than 6 months ago. I did a > 50/50 mix with prestone. The coolant level is fine, I have no leaks so I haven't had to add any water and haven't diluted the mixture.

Does the fact that running the heater will cool off the temperature make sense with a stuck thermostat?

Steve

Reply to
sehaare

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Reply to
Hairy

Yes... the heater is just like a little radiator and can help in cases like this. As you had opined, thermostats are pretty cheap and not too hard to change (even if that's not the root cause, I don't trust overheated thermostats - been bitten before). Tale a look at the AC condenser and another at the radiator front (between it and the AC condenser). Lots of crud can gather in here.... most of it can absorb moisture and still flow acceptably when above freezing yet turn into something impenetrable when below freezing.

Reply to
Jim Warman

Jim, Thanks for the advice. I replaced the thermostat and the problem appears to be fixed. When I first had the problem I thought that maybe I had an ice problem with the radiator and did not find anything on an initial inspection but I'll take another look when its daylight tomorrow just to be sure.

One thing that still puzzles me is that the radiator fan appears to be running continuously even with the engine cold and the Heater/AC controls set to Off. I pretty sure that it should only run when the temp goes above a setpoint or when the A/C is turned on but the Haynes manual that I have doesn't show any schematics of the fan circuit so I can't trouble shoot it. Do you have any advice on that one?

Reply to
sehaare

Don't know which engine you have, but mine has the 3.0 V-6, and it has a gel-coupling that drives the fan.

Which means that the fan always runs -- in hot weather, the gel firms up and the fan turns faster, and under cool conditions, the gel thins out so the fan can turn more slowly.

This is a cheaper, and potentially more reliable, setup than an electric fan.

Alan Moorman

The only reason some people get lost in thought is because it's unfamiliar territory.

Paul Fix

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Reply to
Alan Moorman

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