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Toyota Repair/Corolla Boiling Coolant


Hello. I have a 1994 Toyota Corolla that is having some issues. Namely, it's burning up coolant; I was driving to school the other morning and when I arrived and parked, I noticed large amounts of steam coming from under the hood; the coolant was boiling/steaming out through the overflow reservoir. I checked the radiator and the coolant level was low. I refilled it and it was fine for a few days and then the same thing happened, so I did some further investigation;

The check engine light was NOT on; but I checked for codes, anyway. This being an OBD1 system, I opened the hood and jumpered terminals T1 and TE1 in the diagnostic box and checked the dash; flash flash, pause, flash flash, long pause, repeat; a code 22, "Engine Coolant Temperature Sensor signal" (according to this site:

I bought a new temp sensor, installed it, and cleared the codes (by unplugging the battery). I refilled the coolant, drove it to and from school the next day, and rechecked for codes when I got home; nothing. I figured I'd fixed the problem. It was fine for a couple days. Then, today, on my way home, the coolant was boiling out again. I checked for codes; nothing.

So, I googled how to test the sensor with an ohmmeter; should be ~2000 ohms cold, and drop when heated up. I did this test on both the "new" and "old" sensors; the "new" sensor was ~2700 ohms cold (a bit high?), and dropped significantly when heated up. The "old" sensor was ~2000 ohms cold and also dropped when heated up. Both sensors appear to be good, yes? I put the "new" sensor back in and, again, checked the codes; code 22. That's where I'm at right now. I'm thinking it may be the wiring/connector that plugs into the sensor that's bad. I'm hoping someone here can give me some input :)

Some other notes: at some point in all this, I noticed that the radiator fan was not coming on. I've read in a couple places, though, that they WON'T come on until the coolant reaches a certain temp (200F? 210?) It should've been on when the coolant was boiling, though, certainly? And it wasn't. After I installed the "new" sensor, I meant to check and see if the fan was on when I got home (when the coolant would be hot enough to trigger the fan), but I didn't remember until about 10-15 minutes after I'd parked, though; at that point I went out and turned the car on and the fan came on for a few seconds then shut off. I figured it was had cooled sufficiently while sitting and the fan had come on, sensed the cooled down temp, and shut off again. But today, after it boiled over again, I checked as soon as I got home and the fan was not on.

I can, however, get the fan to come on by turning the AC on, so the fan seems to be working to some degree (could still be a bad starter winding, maybe? I dunno).

Another note; about three weeks ago, the igniter in the distributor went bad and, in the process of tracking that down, I removed and replaced the entire distributor (including cap and rotor and also new spark plug cables) and, thus, had to adjust the timing and all that. The car runs fine, now; no hitching or missing and has good power and all. I don't know if this could have something to do with the current issue or not, but, ya know, the timing of it... well...

Also, during all this, I've been watching the temperature gauge in the dash closely ever since the first incident with the steam. It only ever rose once; when I was on my way to AutoZone to get the new sensor; the coolant had boiled out and I only had a little left in the bottle in the trunk to put in. The temp needle jumped a little past middle, then went down to normal (a bit under midway), then jumped a bit, then down. Other than that one time, the temp gauge has been normal; starts cold in the morning then warms up to just below middle and stays there. Maybe this will info will be helpful :)

Anyways, this is starting to turn into a novel, here, so I'll hit the submit button now. Thank you! :)

hello, the problem is not the coolant temp sensor as you most likely know by now, it is possible that there is a problem with the cooling fan, both fans will turn on by default when the a/c compressor engages regardless of engine temperature, the main cooling fan is controlled by a temperature sensor located on the bottom of the radiator, it has an electrical connector with two wires on it, turn the ignition key on and disconnect this connector, the fan should now run constantly as long as the key is on, if it does drive the car like this and let me know if it still overheats.  

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Ted Ritter


I have more than 28 years experience as toyota technician, I will be able to answer most questions related to the Toyota product line up to the present year models,I am located in the US but welcome questions from other regions of the world. When asking a question please provide specific information: year,model, engine,transmission information. Provide as much information as possible including a brief repair history if possible. I have been a volunteer here for more ten years an have answered over 16,000 questions helping Toyota owners with their problems and save thousands of dollars without any compensation, some of my answers are published on many other websites including google and various automotive forums. DONATIONS ARE VERY MUCH APPRECIATED, IF YOU HAVE RECIEVED HELPFUL INFORMATION PLEASE MAKE A DONATION. AS OF TODAY (JULY 22, 2014) ALL REQUESTED GRAPHICS, ILLUSTRATIONS, DIAGRAMS, PHOTOS, WILL REQUIRE THE MINUMUM DONATION UP FRONT.


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