justinciub

2003 rx300
My car tends to overheat, but doesnt reach close to the red line. My fan wont turn on when the temp gets above halfway mark. I disconnected cooling temp switch and the fans still do not turn on. When i use the ac, fans turn on intermittently. I do see that there are 3 fan relays under the fuse box cover.. Could all of them be bad? Please help?

salimshah

Welcome to CL.

Do you have the wiring diagram?

I am basing my answer on other Lexus vehicles, and there the temp switch provides a path to ground. So if you disconnect the switch then you would not turn on the fan. There could be other parallel switches (a/c on) that can kick the fan on and cycle it as needed.

Salim

maxSteel

You can jumper the fans to verify they work (it sounds like they do though). Driver side fan is for radiator, passenger side is for condenser.

Have you have checked the coolant level in the radiator?

From the diagram I have (if I understand it correctly) it looks like

• Relay 1 or 2 can turn on the radiator fan and they share the same "water temp sw No 1"
• Relay 2 is chained off relay 3. It has 2 positions. It looks like the 'normal ' position will chain the condenser fan and radiator fan together so they both run. When energized it look like it goes to ground so only the condenser fan runs. Maybe with A/C on this design lets either both run at half speed or the condenser only at full speed? No idea.
• Relay 3 is for the condenser fan and has it's own "water temp sw no 2". When energized it will send current through the condenser fan to relay 2.

Given the above if both fans turn on when the A/C is on but the radiator fan does not turn on when the car is hot and A/C off then I think it could be relay 1 or water temp sw 1. To test relay 1, pins 1 & 2 are the switch and 3 & 4 are the relay coil. It should be open when not energized.

fastnoypi

It is possible that your coolant temp sensor has gone bad and not sending its signal to the relay promptly.

justinciub

@fastnoypi @maxsteel @salim
Thank you for the replies. Ill buy a new relay for relay 1 just in case. I had no idea that there are 2 temp sensors. I know one is on the passenger side near the lower side of the radiator. Does anyone know where temp sensor 2 is? Thanks again.

fastnoypi

passenger side of the engine by the upper radiator hose

salimshah

Based on my SC .. 2 sensors ,,, one a temp gauge (analog signal for ecu and temp gauge) and the other is a switch (on path to ground and off open). The switch is the one in the fan circuit. Test is very simple, ground the wire to the sensor and the fan kicks in.

Please verify for RX.

If I find my ref material, I will comment this post.

Salim

salimshah

A member has been kind enough to give me insight to the wiring of RX. Do let us know if we need to dig more or the problem has been solved.

Salim

salimshah

From my analysis if the fan does not come on when the engine is hot, the culprit is ECT1 ,,, which is located on the radiator bottom.

You can disconnect the connector and short the two pins, and the fan should kick in ... just be careful of the hot and running engine.

If that does not work, we may have to trace the circuit.


Salim

Zarkove

Rx300 radiator fans timming
Hello ! New guy here !! I'm having a serious doubt with my rx300 cooling system; it's a 01 model and it only has 1 temp switch closed to the thermostat, there is non on the radiator or even losen plug : what happens that it takes quite long for the radiator fans to kick in and when they do it doesn't take them more than 15 to 20 secs max for them to come off and then it will take at least 5 minutes foe them to come on again , while the engine is running on idle. is this normal ? Shouldn't they run a bit longer ? All help appreciated 😩