Car:
1997 Toyota Celica GT

Location:
Central California(It's pretty hot nowadays since it's hitting summer)

When I started to notice the overheating problem:
My car ran with no over heating problem until AFTER I replaced both the ECT sensors because I had a P0115 CEL code. When I had the code my car would start then idle rough and then stall. So I bought an OBD2 CEL reader and I had the P0115 code. So I replaced both the ECT sensors and the CEL went away. The next day I was driving to Fresno(45 min drive). It drove ok(but I'm not sure because I didn't keep an eye on the gauge) until I started the car again about 6 hours later. At first it was at the correct temperature until about 15 min into the drive and I noticed it jumped up to 70% and back down. That was how and when I started the notice the over heating problem.

Problem:
Overheats once the car has been driven for about 30-40 min. My normal operating temperature is about 45%. When it starts to over heat. It'll jump up to about 65-70% then back down to about 50%. Then slowly to 45% again. Then like after another min it'll jump back up and repeat the process.

I noticed that when I was at a stop. The fan kicked in and the temp gauge jumped up to about 55% then slowly up to 70% then back down to 50% again.

EDIT: Just got back from testing my car and it seems to like to heat up to about 60% right until the fan kicks in. It'll drop to 45% then immediately and slowly climb back up to 60% and then stays there until the fan turns off. It'll slowly crawl back down to 45%. And it repeats itself. I'm thinking I might just have a faulty Coolant Temp Sensor, the one that goes to the ECU and not to the Dash. This was all done while the car was idling. Any ideas?

What I've done so far in order:
1st- Replaced both ECT sensors. 2nd- Replaced thermostat. 3rd- Replaced upper radiator hose. 4th- Flushed out the cooling system. 5th- Bled it out correctly. 6th- Replaced the radiator cap & bled it again. 7th- Checked for leaks, there were none. Coolant level stays the same.

EDIT #2: Ok. So here's an UPDATE. So. I let my car idle and heat up to about 70% and I just let it idle. It kept jumping when the fan turns on and off so I decided to unplug the sensor/switch so that the fan will always be on. When I did that trick. The gauge went down to about 45% and stayed there and never climbed or jump?

When it's connected. The fan will turn on for about 2-5 seconds max. I know that's too short. I think that's why I'm getting these problems. My fan is just not turning and staying on for the right amount of time. What I did was replaced the radiator and the fan switch. So I don't know why the fan isn't staying on for the right amount of time? Any ideas?

EDIT #3: Ok so I finally took it into a shop to test it out and they said my car is not overheating but the ECT unit isn't grounded properly because I had teflon tape on the threads. So I bought a new ECT sensor and installed it without the teflon tape. Results are NOTHING! The only relief is that it's not overheating at all. The gauge on the cluster is saying it's over heating but it really isn't. At least that's according to the mech I took it to. Any ideas about the ECT, PCM, and etc.???

This post has been edited by ILoveMySilly97: Jul 18, 2012 - 7:21 PM

Does it fluctuate like this regardless of whether you are driving or parked, or does it only do it when you're sitting?

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Yea. It flows and everything. I'm thinking that I might've replaced the wrong sensor? I noticed that there are three sensors. There's one on the engine. There's also two more to the right of it (facing the engine). The ones I replaced were the two next to the engine. If you follow the upper radiator hose it'll lead you to both of the sensors that I replaced. Do you think replacing the one on the engine will stop the over heating? What is that sensor on the engine anyways?

sounds like the thermostat, if it gets hot then you haul ass and it goes down, usually thermostat.

Do you have a picture of where the sensors are that you replaced? The description sounds like the coolant temp sensors on the water neck.

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It's been having this problem even before I replaced it with a new one.

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The green circled ones are the ones I've replaced already. The one circled in yellow is the one I'm wandering what is it for?

The two in green are definitely coolant temp sensors, I believe one is for the ECU and one for the gauge cluster. The one in yellow is the oil pressure sensor, if I'm not mistaken. It's been a while since I've had a look at a 5S and a whole lot longer since I've seen a 7A.

maybe you have a small crack you dont know about, i had that problem with a gt before, it would get hot, and i thought it was the thermostat, then one day it was shooting it all into the reservoir. or maybe you have an air bubble in your radiator, if its jumping up like that and then going down. start itup and let it sit there, warm up and see if it gets hot and goes back down.

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When I was bleeding it. It was idling at normal operating temperature for about 20-30 min. The gauge didn't jump up and down at all. It stayed where it should be. There were no more bubbles coming out of the radiator either. Even when I "massage" the upper radiator hose.

You mean crack as in the hoses?

radiator could be cracked, hose could be cracked, could be the clamp not tight enough. my gt, i could drive for an hour no problem then when i would get to a dead stop it would overheat, would haul ass to get it to cool down and then it woud "dump" the antifreeze in the reservoir, small crack on the radiator i didnt see

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So how do you check for a crack on a radiator? I replaced the upper radiator hose but not the bottom.

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Yea. You're correct. It is an oil pressure sensor.

So I popped the hood and checked the engine coolant level in the reservoir. it was low so I added more coolant into it and started the engine. I noticed that it was spitting out coolant out of the hole on the top to prevent it from overflowing. It spit out just about the same that I put jn. About a cup. Now it's not spitting it out anymore?

A crack anywhere in the cooling system would cause massive loss of coolant. Even the most pinhole leak will become obvious whenever the cooling system reaches 5-30 psi of pressure, not sure what ours is but its somewhere in that scale.

Sounds like the thermostat to me. I would reccomend pulling the thermostat and testing it with a pot of bouling water and a thermometer. Thats why it has a reusable gasket

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Everyone's saying it's the thermo stat but I actually replaced it just a week ago AFTER the problem occurred. I actually thought it was the thermostat and replaced it but it didn't change the problem at all.

where did you get the thermostat from? i bought one from autozone that didnt look like the oem one, put it in and it still was getting hot, got a toyota oem one and never had a problem again!

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yea i got mine at AutoZone and it does look like the oem one. I know it works because there's flow.

theres flow, but its a little bit smaller, the one i got didnt look like the oem one for my car, i pulled mine out and the rubber seal broke, id just check it incase

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Working does not mean working correctly. If your thermostat is miscalibrated and opening too late -- at say 90C instead of the proper 82C -- then I could easily see the issues you're having. Proper testing requires bringing the temperature of the pot of water up slowly, so you can tell at exactly what temperature the thermostat opens. I had the opposite issue, my thermostat was opening early, but only by a few degrees below 82C. Rapidly heating the water made it look like the thermostat was working correctly because the reading wasn't precise enough.

The other possibilities which occur to me are the radiator cap being too high a pressure value, thus allowing the coolant to reach a higher temperature than it should, and the temperature sensor on the radiator fan being not turning the fan on at the appropriate temperature.

However, have you checked your ignition timing? You mentioned it was having issues with smooth running, and incorrect ignition timing is one of the possible causes listed in the BGB.

It can also be a clogged radiator. Failed water pump. Clog in the system. A trap air pocket. Weakened radiator fan. Sensor malfunctioning. Bad temp gauge in your dash. Inproper engine ground. Corrosion of that water ways in that water jackets of that block. Crack in engine block. Blown head gasket. Ect ect

Now you have to rule out each one of those problems one by one until you find the problem.

One of that first test you can do is to remove that thermostat and wire your cooling fans directly to the battery and see if it still over heat. If the car does not over heat you know your radiator is fine, your fan is okay, there are no air pockets and your water jackets are fine. Basically this free test rule out half the potential problems.

Do that test and report back.

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I never really thought about those small minor things. Yea I think my ignition timing is a bit off. I don't know how to time it so I'm going to ask my cousin to time it for me. See if it'll stop the minor misfire I have.

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How do you wire the cooling fans to the battery?

You unplug the fan and you run a wire to each one of the terminal with Some Terminals. You can buy the wires and terminals at any hardware or parts store.

cant he just pull his temp sensor and see if they turn on, if they dont then he knows they are bad?

also the for the air pockets, cant he just take the radiator cap off and let it run, while it sits there?


usually if your ac doesnt work even if everything is correct, it would be the water pump

This post has been edited by zfjohnson07: May 26, 2012 - 8:36 PM

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Actually my AC blows COLD and it's already bled and I have a new sensor.

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Okay. I suck and scared of things when it comes to wires. I don't know why. Lol. Just always been like that. I'll have my in law do this test for me.

ill show you an easy way tomorrow

Just got back from testing my car and it seems to like to heat up to about 60% right until the fan kicks in. It'll drop to 45% then immediately and slowly climb back up to 60% and then stays there until the fan turns off. It'll slowly crawl back down to 45%. And it repeats itself. I'm thinking I might just have a faulty Coolant Temp Sensor, the one that goes to the ECU and not to the Dash. Any ideas?

This post has been edited by ILoveMySilly97: May 27, 2012 - 2:18 AM

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Which one is the one that goes to the gauge cluster? And which one is the one that goes to the ecu?

2 wires sensor for ECU / single wire one for gauge.

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To see if I have this right.... 60% the fans kick on, drops to 45% fans still running, climbs back to 60%, fans still running, fans then shut off, and then it drops to 45%?

if it climbs to 60% before the fans kick on then after the fans kick on it slowly drops back down to 45%((as in your first part of the description) and then repeats this process, I would suspect the ECT/water temp switch on the bottom of the radiatior as being bad.

I know on my 94 GT 2.2 the fans kick in before the gauge moves off of normal operating temp (about 45% on the gauge). My gauge doesn't move much off operating temp. I just was testing other items on my car, pulled up an 6-8% grade for about 10 miles, 3rd gear, about 5200 rpm(approx 65mph), A/C on, outside temp of 100 degress and the temp gauge didn't budge. I was also idling for about 30 min, in 108 temp, no A/C. Fans cycled on and off, temp gauge stood steady the whole time.

Here is a link for cooling fan troubleshooting for my '94. click here

I'm not sure about the second part of your description, fans shutting off at 60%, and then the temp magically cooling down. Would make more sense if your situation was fans kick on at 60%, cools to 45% and fans shut off, then repeats the cycle from there.

As a side note they must of made those '97 much quieter than my '94, cause there is NO way I can hear my fans kick on and off rolling down the road!

Well my 94 GT doesnt fluctuate once it reaches operating temperature. It stays exactly in the middle of the gauge no matter what type of driving I do. Youre going to need to test each of the three sensors with a multimeter and a pot of boiling water to the shop manual specification.