Help! 98 Camry Overheating, Have multimeter!
 

Ok here is my trouble shooting thus far with a multi meter.

The Engine Fans Work, but they only want to turn on when the A/C is on, and even then it overheats
-Fans may not be staying on/cycle with compressor
-Water Temperature Valve not opening

I tested 3 fan relays
-#3 appears to be a SPDT Switch with 1 N/O and 1 N/C set of contacts, when powered both contacts open/close
-#2+1 relays are just SPST and close when powered

This leads me to believe that there is one or more relays in the circuit (saw somewhere/something about and engine relay to test, don't know which or where) or that the water thermostat is not working, or a combination of both.


Any tips??


Also, I'm going to check to see if the thermostat works by checking if the water line out near the oil filter gets hot when the engine runs.

ok well the pipe (1-2" black hose) that enters the top of the radiator gets hots, the other pipe that comes from the bottom then goes into the engine near the oil filter doesn't

I drove around for a bit and got the engine at about ~2/3 of the way up, pulled over and the fans were not running. Again they only turn on for the A/C. Didn't see any leaks, except that a lot of water is pushed out by pressure from evaporated water after the engine was turned off. Doesn't look like and belts are broken, there is a guard covering what looks like a possible water pump.

Anyone?

The fans have several modes of operation.

The fan system activates when AC is switched on and cycles on/off as the compressor cycles on/off, they don't stay on 100% of the time. This is hard wired and has nothing to do with the coolant temp.

If the fans work with the AC, at least some part of the relay system works.

The fans also come on when the water temp switch opens at around 199F. This switch is located on the firewall side of the lower radiator tank.

To test the radiator relay system, remove the electrical plug from the water temp sensor switch. When the plug is disconnected the fans should turn on (assuming ign switch on), this operation when unplugged from the switch is opposite of what you might expect.

The purpose of the fans is to pull air through the radiator when the car is moving to slow to accomplish this. When the car is moving the coolant system should be able to cool the engine without the aid of the fans.

The Camry coolant system should be able to maintain a safe temp even at idle. The coolant will heat up and once reaching the set point of the switch on the radiator turn the fans on. The fans will cycle as the coolant temp cycles. If the fans are not cycling the coolant will overheat.

The temp gauge on the dash has its own temp sensor. The gauge needle should stay in the normal position (typically not even move) as the coolant fans cycle on and off.

If the engine overheats as indicated by the gauge when driving there is an issue with the cooling system. The fans should have come on, yet if the car is moving fast enough there should be no need for them.

The timing belt powers the water pump. If the engine runs the belt is OK and the pump is rotating. It rare but happens that the pump impeller fails or degrades to the extent the engine will overheat.

Test the fans as per above, if they come on when the plug is removed the relay system is working OK.

Install a thermometer in the radiator fill point. Start engine and allow the coolant temp to heat up. The fans should turn on before the coolant gets to say 201F. If the temp gauge needle starts to rise and the coolant is above 201F the temp switch may have failed.

When doing this also view the coolant (wear safety glasses!), as the T-stat opens the coolant will circulate and move. If it doesn't the T-stat may not be working. In this case it is possible the coolant in the lower radiator tank is not getting hot enough to activate the switch before the engine overheats.

Sometimes the coolant system become plugged, radiator or engine.

ok Fixed the bad thermostat:

Attachment 4157

Fans are still not coming on, unless A/C is on, however this time the fans kept it from overheating.

Thank you very much Joey P!

Very good info, I will unplug the temp switch and see if the fans come on, if they don't I'll try metering the temp sensor/switch and see if it is opening and closing at all.

ok cool, with the temp sensor/switch unplugged the fans stay on, so now its definitely the sensor.

Thank you very much, yours and another camry forum got this booger fixed.

Good job on running down the problems!

If you remove the temp switch you can test it in hot water. The switch should open when the water temp is above 199F.