1998 Camry Overheat Problem
 

My old 1998 Camry v6 got overheating problem after I mistakenly drove it on Second mode (instead of Drive mode) on highway for 5 min recently. I've tried to
add coolant, change thermostat and the temp sensor, the problem alleviated a little bit but still existed. I did notice that the fan will not work even the temp is high so I am guessing there's probably some electric problems. The weird thing is there's no code on computer and the fan is OK (cause it's still works when AC is on)

I'm wondering anyone here can offer some help... Any help would be appreciated. Thank you!

Can you describe what happened before the overheating? You drove the car in 2nd gear at high speeds, how high did the engine RPM get, over red line?

When and how does the engine overheat? Overheat at engine idle, stop and go, hwy speeds?

The fans pull air through the radiator at low MPH or when stopped. AT higher MPH the air should be flowing fast enough to cool the radiator.

The fans typically kick in at a coolant temps of around 199F.

If having electric fans you can test them by removing the electrical plug from the temp sensor on the bottom of the radiator (ign on). The fans should turn on.

The coolant system has several temp sensors, one from the computer, one for the temp gauge, one for the fan operation.

The coolant sensor for the computer may monitored by the computer and thus trip a code but the other 2 switches are not. Overheating will not trip a code unless it causes other system monitored by the computer to have problems.

Thank you for your reply. I really really appreciate your kindness and knowledge.

The RPM was around 6000, it stayed just at the edge of the red area of the RPM gauge when I noticed it. I was driving in local for about 5 min, and on hwy for another 5-10 min. The speed is around 65 on the highway.

I haven't tested it in driving condition actually, now the temp gets to the red zone after around 15 min idle, and the fans never kick in...

I will do the plug test as suggested. Thanks! I didn't know there are 3 temp sensors before, I guess my friend changed the one from the computer (called ECT, right?), cause the computer gave a code P0115 when we didn't wire it correctly. The one for temp gauge should have no problem, but where is the one for fan operation? Can you show me where it is? thank you very much!

15 minutes at idle or driving speeds?

Yes, ECT Sensor is often referred as the computer temp sensor but Toyota uses this abbreviation ECT Switch for the fan coolant switch.

The ECT Switch is just that, a switch. Turns on and off (no in-between) in response to coolant temp.

The sensor for the fans is located on the lower radiator tank, engine side, below the passengers side fan.

The fans should kick in at 208F.

How does the engine run, idle OK?

Thanks! I will take a look at the ECT switch. Basically if it's not the sensor, it must be the ECT switch or the wire between them. Right?
Should I check any fuses? From the repair manual, there's a thing called "cooling fan relay", is it related? I guess since the fan still ran under AC, the fan main relay, cooling fan should be OK.

15 min at idle. The engine sounds OK. That's the last thing I wanna think about...

Remove the wiring plug from the switch. The fans should turn on.

Note: if the fans run when the AC is on, the wiring to the fans should be OK at least one or two relays. As I recall there is more then one coolant fan relay.

I checked the repair manual and there are 3 cooling fan relays. I am wondering whether the AC uses totally different repay or not. If they use these relays too, it means the relay should be OK, right?

Which repair manual are you using?

The fan system is a little complicated. I sent a private message with a link that may have better info on the how the system works.