91 Camry Temperature Problem

Replace the thermostat and use a genuine Toy one, I have a 91 and on several aftermarket the gaskets leak since they are to small and it always bypasses cold water, Have you ever flushed or changed the cooling system, if you see any buildup on the coils looking inside the radiator you should flush it now, as that build up can be in the heater core also. Dont use more than 50% antifreeze. And if you do that , might as well do the hoses. Coil on your model is an issue, do you live where there is salt on roads, next is brake and fuel lines rusting out.

You're describing a classic temp sensor circuit problem. If there is an open in the circuit, the computer thinks it's around -40F, downshifts, and starts pouring fuel like you just started the engine. The temp sensor is ususally the culprit when it comes to intermitent occurences like this (about 60 bucks, screws right in).

Yes to both. You should check to make sure that the thermostat, after all these years, didn't stick open and overcool the engine (plus that your cooling system is in top shape by changing the hoses, coolant, etc).

You also want to check to make sure that the engine coolant temperature sensor, which is important to many other engine functions, is working correctly.

Haynes manual does a good job tell you how to check. Or look > You're describing a classic temp sensor circuit problem. If there is an

I have a 91 that also had a similar problem. Replacing the thermostat solved the problem. I live in California and it usually doesn't get very cold here, but the car sometimes downshifted when I was going downhill and the load on the engine was minimal. I always took the slow warm-up for granted, until I received an advice from this NG to replace the thermostat. Since then no more downshifting.

Thanks to everyone for all the suggestions. The thermostat was definitely the culprit. I could see the difference the moment that I drove the car after replacing it, because the temp gage started going up a lot faster, and didn't take forever like it used to do. The heater warmed up a lot faster, too. I got the thermostat and gasket from the dealer, and they were about $22 all together.

However, this was no 10 minute job. The huuuuuuuuuuuuuuuuuuuuuuge problem was getting the @!*^&# nuts off that hold the thermostat on. I was able to get the top one off without too much trouble, but the bottom one just would not come off. Because of where it is, the bottom nut is very hard to get to, so it's not very easy to get the appropriate leverage on it. I tried about five different tools (which included a couple runs to the store), but was finally able to get it off with a ratchet head and a pair of vice grip pliers (along with a bucket of elbow grease).

I also changed the oil and flushed out the cooling system and replaced the coolant. In the process, I somehow managed to break the top plastic part of the coolant vacuum sensor (I think it was old a brittle), so I had to replace that for $56 (ouch!).

Now, I just have to replace the ignition coil (been having the problem with it stuttering and stopping in wet weather), and the car will be in fine shape (at least on the inside).

Thanks for all the help.

Steve

Try cleaning the coil first with alcohol on a rag and spray electronics cleaner