Vehicle Overcooling!

My 89 Escort is STILL overcooling at highway speeds after replacing the thermostat. When the vehicle is at idle it reaches to operating tempature. I can't think of anything else that might be the problem other than the TCC being faulty, if it even has one....

Also would overcooling cause lower than normal MPG?

That would lower your mileage because the engine, thinking it is cold, will run rich. The only thing I know of that can do this is the thermostat. The one you bought must be defective.

Some people in cold weather areas restrict the air flow through the radiator by partially blocking it with cardboard, sheet metal, or canvas.
What temp thermostat did you install?

I read in another post that the vapor bypass in the thermostat housing will make it run hot in idle and cold down the road. They said to take off the housing and shake it. If it rattles it is bad. You can't get this at the parts place and the dealer would be too high. They reccomend getting one at the boneyard. I read this and don't know it to be a fact.

Make sure the fan isn't staying on. I noticed with my 1990 Escort the fan kicks on in any weather when I use the defogger for the windshield if you have air conditioning, and also in the mixed position which will turn the fan on for a brief period of time. Also, there is a thermal switch on mine that is screwed directly into the back of the thermostat housing which turns on the fan. Make sure that is operating properly.


I read in another post that the vapor bypass in the thermostat housing will make it run hot in idle and cold down the road. They said to take off the housing and shake it. If it rattles it is bad. You can't get this at the parts place and the dealer would be too high. They reccomend getting one at the boneyard. I read this and don't know it to be a fact.

One other thought, make sure the engine is really running cold and the temperature guage isn't lying. I think there is a voltage regulator behind the dashboard panel that regulates voltage to the guages. Also, trace the wires going to the guages and make sure they are not loose. If your heater feels luke warm after warmup with the heater fan on high then the engine may really be running cool. Electrical guages are not usually very accurate so the best way to check is to get a thermometer and test the temperature of the water. The thermostat on my 1990 Escort opens between 192 to 195 degrees. Make sure you have the right thermostat for your car. I don't know if the 1989 Escort is the same one. Hope that helps. Good luck.

'89 Escorts use the same thermostat at the 90 model. The Escort isn't a hot running engine anyway. If you're running a stock engine, and it's cold, run a 195 degree thermostat. If it's summer, and you like to have some headroom for the hot days, run a 180. If you have engine mods (shaved head, upped compression, advanced timing) run a 180. I run that in mine, and my temp gauge hits the edge of the normal bracket, even on hot days....and I've got a 10.25:1 comp. ratio.

Alright thanks for the replys, the thermostat that I bought is at 195* F. Also now that you mentioned about the thermo housing, the bypass check ball rattles when you shake it. So I'll be checking into that when it gets alittle warmer outside.

I went through this for a whole year and finally resolved it early this year. There is a very lengthy message list regarding the details of this. Do a search in this forum for: 1995 Escort overcooling problem
posted by willye. I hope this saves you alot of trouble.

Replaced housing with another one from a junkyard, shaked the semi new housing and heard the same rattle as the old one. Still overcools when driving.

I realized that my hood doesn't have that foam/fiber glass insulation under the hood. Might that be the problem? Does anyone with the same overcooling problem have the foam/fiber glass insulation under their hood?

Cover up about 1/2 the area of the radiator with a piece of cardboard. With the thermostat you are controlling the amt. of coolant reaching the radiator. This way you will be controlling the amt. of air through the radiator. Truckers have been doing this on their big rigs for a long time. Give it a try. I don't see the lack of insulation having any bearing on your problem.

Recent thread wrestling with overcooling....

http://www.automotiveforums.com/vbulletin/showthread.php?t=486552

I'm thinking of another possibility...The tstat does not seat really firm in the housing (in fact, the aftermarket ones seat better than the Motorcraft OEMs)...you'd think pressure on the engine side would keep it pushed firmly in the seat but maybe at times pressure is higher on the radiator side and cocking the tstat in the housing - creating a coolant bypass around the closed tstat. Be worth some trials - cold start and check time to pressure in upper rad hose.

When I get back in the ring to rassle with this demon, I may try an RTV ring where the tstat seats.

Also, that rattle...my 2 old ones rattled....bought a new one from rockauto (~$45? - anyway, dealer wants $140)...new one rattles just same...I'm not sure that shows defective.

The rattle is due to a ball bearing floating in the little bypass line. It's the little line next to the big one. It's in case the thermostat is blocked...and to relieve pressure buildup when the thermostat is closed. It's not a defect at all, just a good idea. And don't worry about overcooling so much, unless your oil doesn't get hot enough. Trust me on this. I run my car cold, and love it. No complaints, aside from it taking a while longer to heat up.