Howdy all, and thank you for all you have done in the past, you have done so well I have not had to register until now.

Single Overhead cam motor which ever one that is...

Coolant Fan will not come on.

AC system functional...
Coolant Fan checks out as ok as per jumper wire at relay...
Relay checks out as per swapping with AC relay not to mention I have a few others laying around...
No codes thrown as per OBD II reader...

Only two other possibilities exist to my knowledge,

* Temperature coolant sensor or

* On board computer bad ground/ground wires (heaven forbid)

I have no idea how to diagnose either....

any suggestions?

Thank you! again!

Tuscoro


PS... even with jumper wire in place to cause fan to work, it seems it is still difficult to keep the engine cool, in short it seems sensitive,
Example, on the freeway or at speed near or above 40 MPH, no problem, but in town with fan operating WITH AC on, it still seems to climb to quickly into unsafe temperatures. Not long ago I never had a problem unless siting in a parking lot on a hot day idling with AC on... its a given...

 

First things first, have you ever replaced the thermostat and are you running a 50/50 mix of coolant and water? Thermostat could be sticking making it run hot, but perhaps the coolant temperature sensor is bad.

 

Do you have a voltmeter or multimeter? If you do, check for voltage on each of the sockets for the fan relay. Two of the sockets should always have 12v when the key is on.

If you have 12v, then you probably have a ground wire issue to the computer.

 

Thank you for your responses, Rubehayseed, yes I am running a near 50 50 mix and no I have not replaced the Thermo since I got the car... good points to consider, Thank you....

Keith, thank you as well but please re-read your response, on one hand you say I "should" have 12 V at two terminals, and then you say if I do I have a ground wire problem? Please clarify...

Using a voltmeter I have at pole # 87 and 30 12 V and at 86 I have an absolute ground and nothing at 85... which makes sense to me.. so I am going to replace the Temp Sending unit and see what happens....

Thanks Again.

 

You have two sockets with 12v on them, then you have two sockets that have to find ground in order to complete the circuit. One of them finds ground through the fan motor and since when you jumper the sockets to pass 12v to the fan, the fan works, that ground is good.

The ground for the relays coil comes from the computer. When the ECU gets the inputs it needs to tell the fan to turn on, it forward biases a junction and provides ground for the coil, that throws the relay and the relay provides 12v to the fan motor.

The ECU is pretty reliable. Usually the issue is a broken wire between the relay and the ECU. When I sold my Saturn, I gave away the factory service manuals that I had so I can't tell you which pins to check for continuity between the relay socket and the ECU.

You can look at the ECU connectors because they are right behind the battery but to check the relay socket, you have to remove the relay and fuse panel.

I think you should check for other things as well. Your symptoms indicate that the water pump may have failed, but the OEM water pump is pretty robust as long as the seal holds. If you have an aftermarket water pump, well all I can say is that the quality varies on those.

One often overlooked item is the radiator cap, but the usual symptom for that is the temperature will rise when you are going uphill and then return to normal when descending. It will also overheat at high speed.

 

One more thing to check is the fins on front of the condenser for the AC. It can get plugged up with bugs, or just bent over to the point that air can't get through to the radiator.