91 corolla stuck thermostat? - Toyota Nation Forum : Toyota Car and Truck Forums

billsif · 11-22-2006, 08:24 PM

i have a 1991 corolla that seems to have a problem operating at the right temperature.
when i drive around town (around 35 mph) and it's cold out (lately around 35 degrees fahrenheit) my temperature needle doesn't get farther than 1/3 of the way up the gauge from the cold mark. the heat works okay, but after it's on for a few minutes the temperature gauge starts to move in reverse, back down toward the cold mark. If I get on the highway and drive around 55 or so, the needle moves way down to cold and the heat just barely works. The problem is that my transmission shifts out of overdrive to 3rd gear, the rpms skyrocket, and the heat isnt very hot. Sometimes I have luck turning on the air conditioner to put some extra strain on the engine so I can get the needle to rise slightly above the cold mark so the transmission will upshift. Is my thermostat just stuck open or could I have another problem? Is the thermostat fairly easy to replace on a 91 corolla? Thanks.

retiredat44 · 11-22-2006, 08:32 PM

Since a new one only cost a couple bucks, and it's probably the problem try it, but drain some of your antifreeze first so you don't lose it.. and maybe buy some more incase you do lose some..

IMHo

Quote:

Originally Posted by billsif

i have a 1991 corolla that seems to have a problem operating at the right temperature.
when i drive around town (around 35 mph) and it's cold out (lately around 35 degrees fahrenheit) my temperature needle doesn't get farther than 1/3 of the way up the gauge from the cold mark. the heat works okay, but after it's on for a few minutes the temperature gauge starts to move in reverse, back down toward the cold mark. If I get on the highway and drive around 55 or so, the needle moves way down to cold and the heat just barely works. The problem is that my transmission shifts out of overdrive to 3rd gear, the rpms skyrocket, and the heat isnt very hot. Sometimes I have luck turning on the air conditioner to put some extra strain on the engine so I can get the needle to rise slightly above the cold mark so the transmission will upshift. Is my thermostat just stuck open or could I have another problem? Is the thermostat fairly easy to replace on a 91 corolla? Thanks.

diver9000 · 11-22-2006, 10:22 PM

I have also seen where low fluid levels can cause such a reading. Have you checked to ensure the antifreeze/water level is full? While you are doing the thermostat check both hoses that run to and from the heater core; make sure they have good connections on them. Good Luck

cheesep · 11-23-2006, 12:52 PM

You're describing a weak or stuck thermostat. The first thing I would do is change it. When you take it out, it may look okay but if you put it in a pot of water and bring it to a boil you'll probably see that it will open way sooner than it should.

Low fluid is not the problem. If the coolant was too low, driving on the highway or stressing the engine as you've done would cause the engine temperature (and the guage) to go up, not down because you wouldn't have enough coolant circulating through the engine to properly cool it and it would begin to overheat. On the other hand, you wouldn't have heat in the passenger compartment because there would not be enough coolant in the system to circulate through the heater core.

I would replace the thermostat, make sure the fluid levels are good, and drive on . . .

billsif · 11-26-2006, 07:02 PM

well, i attempted to replace the thermostat and after removing the upper radiator hose came to the conclusion that the thermostat must be located in the engine end of the lower radiator hose. is this true? if so, does anyone know what size socket to use on the two nuts? it looks like the thermostat housing slides onto two studs and two nuts are used to hold the housing in place? should i take the battery out to get to the thermostat? please help me out. thanks.

punter · 11-27-2006, 05:26 PM

It's on the top hose in mine. Yours will be the same.

Take the top hose off then remove the front of the themostat housing. IIRC It's the part that the hose is clamped to.

diver9000 · 11-29-2006, 06:18 PM

So did the thermostat get fixed or what?

billsif · 12-03-2006, 10:21 PM

no, actually it still didnt get finished. i live in an apartment with little room to work and now it's freezing cold out. the car is still operating at very low temperatures. i took the upper radiator hose off and removed a housing-type piece which was way too small to house the thermostat autozone sold me. when i took the housing off i saw what appeared to be a square opening into the engine. there appears to be another housing-type piece at the engine end of the lower radiator hose, which i was unable to access because of the battery and air cleaner housing being in the way, and my lack of a 10mm socket or wrench. i believe the thermostat is in that housing piece on the transmission side of the engine and does not have anything to do with the upper radiator hose at all. if someone could please confirm this i would be very appreciative before i take my time removing the battery, air cleaner housing, and anything else in the way in this 10 degree weather. you might be right about the upper radiator hose, but from what ive seen i dont think so. thanks everyone!

retiredat44 · 12-04-2006, 03:38 PM

Quote:

Originally Posted by billsif

well, i attempted to replace the thermostat and after removing the upper radiator hose came to the conclusion that the thermostat must be located in the engine end of the lower radiator hose. is this true? if so, does anyone know what size socket to use on the two nuts? it looks like the thermostat housing slides onto two studs and two nuts are used to hold the housing in place? should i take the battery out to get to the thermostat? please help me out. thanks.

it's driving me crazy how somehting so simpl ehas anyone puzzled, there's the directions..

http://autozone.com/servlet/UiBroker...3d8016a207.jsp

sad part it you were 1 minute away from fixing it..

diver9000 · 12-05-2006, 05:53 PM

Nice write up Retiredat44. I hope billsif can follow that. It doesnt get much easier. I know its cold but better to fix it in the cold than in the wet & cold.

retiredat44 · 12-05-2006, 06:11 PM

Quote:

Originally Posted by diver9000

Nice write up Retiredat44. I hope billsif can follow that. It doesnt get much easier. I know its cold but better to fix it in the cold than in the wet & cold.

I don't mean to come down hard,, or be rude,, but geeesh,,, it's soo easy....

diver9000 · 12-06-2006, 06:38 PM

Well, thats true. But if he is doing it for the first time and has no one to help him, maybe he is a bit reluctant ya know....Not all of us are blessed with a wrench in our hands. But good info for sure. I hope it is helpful to him.

ghost_ryder35 · 12-07-2006, 11:45 AM

i changed mine yesterday, already had the coolant draied (was doing timing belt and water pump) took less than 2 minutes to change the thermostat. It's easier if you remove the battery so you can get a ratchet in their with an extension.