xsohaib

Since yesterday my car has been overheating but the symptoms are rather strange. I recently had the valve stem seal job done as well as the port and poilsh on the head.
Yesterday at night I start the car around 2:00am to come home from school and after about 7-8 minute drive the car starts to overheat, I panic and shut off the car, check under the hood and everyhting seemed fine (coolant level normal, no smoke etc), I sat back in the car and started it and the temperature needle was still high, for some reason I decided to turn on the airconditioner, and the temperture went downback to normal, no problems the rest of the way home ( a 3-4 mile drive up and down the hills). Then this morning, I started the car and sat at idle to see of the temperature would go up, but it stayed at normal, initially I had the A/C turned off and then I turned on the A/C and still no problems. Then I drove about 7-8 miles often WOT, and in a hilly area to see of the temp gauge would go up, but it didn't.
Next I go for a car was and after about an hour or so, I start the car and within 3-4 minutes the temp needle starts climbing, but this time the A/C was on. So I decided to press on the gas and revved it to like 5-6k rpms, while the car was idling and then the temp went back to norma. The rest of the drive was at normal temperature. The fan I checked in the morning was working fine, What could the problem be?

Thanks in advance for the help

Sohaib

ArmyofOne

I'd say you have a faulty or intermittently faulty thermostat or coolant temp sensor. I dont know how much you know about cars, so I will assume not alot. Your coolant system is pressurized, so it has a waterpump. Your waterpump cannot be the problem, because if your waterpump is bad, you would either be leaking, or you would overheat in 5-10 minutes under all circumstances. You say its intermittent, so we can rule that out.

You have had a coolant flush recently if your heads were done, because coolant has to be drained, and the mechanic that did the heads did a flush of the block if he is a good mechanic. so thats not the issue.

that leaves a few other components, radiator, hoses, and thermostat and coolant temp sensor.

start with the thermostat because they are the cheapest (except for hoses). the t-stat controls the flow of coolant through your motor, based on a reading from the coolant temperature sensor, somwhere in your system. usually right in front of the t-stat. if the t-stat opens only halfway and stickls, yoru engine will take about 5 minutes to heat up, be slightly hotter than normal. if the t-stat sticks in the closed position, you will overheat almost immediately (like 5 mins max in hotter climate, 10-15 in temps below 20 F). If your tstat is stuck open, your engine will take forever to warm up as coolant will constantly be flowing, thats if it warms up at all.

this brings us to the next part, the coolant temprature sensor. If it is sending your ECU a faulty reading your thermostat opens only to the setting the ECU tells it to. therfore, that could be your problem as well. but its not as likely being that the problem is intermittent. i would shoot for themostat first.








whew, im fairly long wided tonight LOL.

xsohaib

Cool, I can have it checked out tommorrow.

ArmyofOne

theres more^ stick around, im nto done editing.

ArmyofOne

there, im done

xsohaib

Thanks, I will have it checked out tomorrow, I was initally thinking about the fan being intermittently faulty but I didn;t think about the thermostat.

Thanks
Sohaib

ArmyofOne

Damn! I forgot about the fan! yeah that too could be the culprit, still leaning toward Tstat or CTS.

Pheonix

Fan is hydraulic. Failure rate is so low it's joke (as with it's simple ECU).
75% of the time after work is done & you're overheating, it's because someone didn't plug the connector in on the powersteering pump. The other 25% of the time the thermostat is installed incorrectly, or is faulty. The powersteering line on top of the pump that feeds the motor has a solenoid on it that let's it go from low flow to high flow.
(It's a 2 speed system, it's either low, or it's high)

From the top



From the access panel





In the Diagnostic port, if you jump OP1 & E1 with the engine running, the fan should spin very fast. if it doesn't spin up there's an electrical problem. (It's best to inspect visually & by the diag port)





If the fan & Thermostat are OK, I would warm the engine up & do a compression test, or leak-down test. Be sure to WRITE DOWN THE RESULTS. The tests are useless without results. After that replace both pressure caps.

Radiator cap - 13.5-17.8psi
Intake cap - 12.1-16.4psi

xsohaib

I replaced the thermostat today (man was it a pain to get to, I had to remove the alt. belts to get to it), and then I started up the car, initially it stayed at the normal temp for a few seconds and then the heat gauge started to rise quickly. Prior to replacing the thermostat, upon visual inspection the fan ran at both high and low speed. Anyways, the wierd thing is that if I stomp on the gas while the car is in "P", and fluctaute the rpms between 4-5k rpms, the engine starts to cool down quickly back to the normal operating temperature! Soooooooooo, what next?


Sohaib

xsohaib

I have temporarily got th problem fixed, I removed the thermostat and the car is operating fine at the normal operating temperature. The mechanic here in the caribbean looked at it and he said that the problem in addition to the thermostat is the fan (which I personally don;t think so). I jumped the two terminals in the diagnostic port and the fan did indeed run at high speed. Anyways, now it is at least temporarily fixed to the point where I can ship it back to the states, and in a couple of weeks when it arrives in Maimi, I shall have the local toyota dealer have a look at it and put the thermostat back in it before I make the drive back to Boston!

Thanks everyone for the advice

Cheers
Sohaib

Pheonix

Ya forget the fan. That thing is fine. All ya need to know aobut the fan is it has two speeds low & tornadoe generator. most mechanics try to say something like "Oh well the motor has play in it & I can stop the blades by touching them". Ofcorse it does it's a fluid motor.

Something is clogged, causing low pressure, or the water pump fins are non-existant
' causing low coolant flow.
As cheap as they are yuo can always give those pressure caps a try.

xsohaib

Man, that is exactly what the mechanic said "look I can stop it with my hands", I did change the pressure caps and also had the radiator cleaned (since labor is cheap in the caribbean, it was cheaper to do that than to replace radiator), then also, the mechanic opened the front cap and while the engine was running, (and the thermostat at this point had already been removed), he increased the throttle a little bit and the coolant was flowing fine through the radiator (when standing in front of the car it was moving left to right). The problem is that nobody has another thermostat for the car in the entire country, otherwise I would have wanted to try another thermostat. But oh well

It is amazing how you pin pointed EXACTLY what the mechanic said

Thanks
Sohaib

ArmyofOne

It is your tstat, its faulty.