electric radiator fan test

[ingin12]

I have an electric fan as well as the normal mech fan clutch fan (2 fans) in my 94 XJ. When I have the air con on, the electric fan comes on ok. I understand that if the temp gets excessive, the electric fan will come on (without the air con being on) as assistance to the mech fan.
Last week, my engine got pretty hot (hot day and in city traffic), but I am not sure the electric fan came on. Normally you can hear it, but this time I could not. Is there a test that I can use to see if the sensor is working? or somehow prove the fan is ok before we get really hot weather.

Thanks Ingin

[Gtscott]

my brothers 94 xj decided it wouldnt come on even if overheating, unless the aircon was on, so i ended up putting a fan controller on it

[ingin12]

Hi GTscott, Do you have details how you did this? Did you pick the relay by way of a dash switch? I am going to guess that I will have to do something similar.

Regards Ingin

[dazza96]

the sensor that screws in to the thermostate housing is what triggers the fan when overheating cheers daz

[rainman]

on the 94 the dash temp gauge sensor and the temp sender for the computer are different.
the service manual has the specs for the computer temp sender (in the thermostat housing)
so you can pull it out and test it.

[ingin12]

Thanks for the info. I have studied the wiring schematics and I cannot find any schematics for the Power Control Module. The ground for the relay pick is from K4 and enters the PCM at plug contact 2. This ground needs to be applied to pin 31 of the PCM to allow the relay to pick and thus applying power to the fan via its contact points. BUT what the hell goes on in the PCM is anyones guess without schematics. How does the ground from pin 2 get to pin 31?
Anyone know where I can get them?

Thanks Ian

[rainman]

my understanding was that the pcm controls the grounding of the fan relay. the pcm turns the fan on on when it turns on the air con. and it can turn the fan on when it sensors the engine coolant gets to hot (~105*c.) hence if the sensor is not working properly the PCM may never decide to switch on the fan.

[ingin12]

Hi Rainman,
What you say is correct. The fan does come on when the air con is used, but not when the engine get really hot, so you are correct in suggesting that the sensor in the thermostat house may be cactus. If it is just a simple on/off contact switch, I would assume by shorting the two contacts in the plug, I should get the same effect of an over heated engine. Does that gel with your thoughts? I think that I will pull the thermostat out and see if I can get it working in boiling water i.e to see if the "switch" in the sensor closes and conducts.

Thanks for your help

Regards Ingin

[rainman]

dude it is not a simple on of switch it is a temp sensitive variable resistor.
hence the test procedure/ resistance v temp paramaters for the sensor outlined in the fsm

[ingin12]

OK, now I understand a bit more. At cold, my sensor is showing 19.6k ohms, the fsm shows at 100F or 37.7c, it should be 1365 ohms, that is 14 times the value at 100F deg. I will now run the vehicle to get it to operating temp to see if changes.
It is pointing to a duff sensor

thanks for your help

regards ingin

[Billnick]

Keep in mind that the temp wont get over 100* C if the system is not pressurised.

I keep telling the missus the food is not going to cook any faster by turning up the gas if it is already boiling.

[ingin12]

I have just run the jeep for about an hour, the temp gauge is sitting nicely at its normal position, at about 80c and I checked the resistance of the sensor and it shows 1197ohms. That is a huge difference from when cold 19.6K ohms. The FSM indicates the resistance of the sensor at 104.4 c (220F) should be 93.5 ohms so I am guessing that the sensor is faulty as it should be reading 93.5c.

Billnick, I am not sure what you mean by pressurised, all modern radiator systems are under some pressure otherwise the water would boil at 100c, clearly not a good thing.

Thanks for all the help

Regards Ingin

[Billnick]

Billnick, I am not sure what you mean by pressurised, all modern radiator systems are under some pressure otherwise the water would boil at 100c, clearly not a good thing.

Thanks for all the help

Regards Ingin

All I was saying was not hold the sensor over the spout of the kettle expecting it to go over 100*. A leaking rad that wont hold pressure will do the same thing. I know its basic but y'know.:)

[Deezelweazel]

Use veggie oil instead and you can go over 100°C

[junglejuice]

I have just run the jeep for about an hour, the temp gauge is sitting nicely at its normal position, at about 80c and I checked the resistance of the sensor and it shows 1197ohms. That is a huge difference from when cold 19.6K ohms. The FSM indicates the resistance of the sensor at 104.4 c (220F) should be 93.5 ohms so I am guessing that the sensor is faulty as it should be reading 93.5c.

Billnick, I am not sure what you mean by pressurised, all modern radiator systems are under some pressure otherwise the water would boil at 100c, clearly not a good thing.

Thanks for all the help

Regards Ingin

80* is too low for normal operation.....

[ingin12]

As a newbie to Jeeps, I am not too sure about how to determine the operating temperature of the coolant. JJ indicates that my guess of 80c is too low and I am wondering if I am at fault in guess it to be 80c.
Attached is a photo of the tem guage after a run, and this is where the needle normally sits in outside temps of 15-20c. On hot days, 26-30, the needle is at the 100c mark.
Can anyone tell me what the temp is by my guage and is it too low for normal running (15-20c) and is it normal to be 100c in temps of 26-30.

Thanks Ingin

[ingin12]

Sorry, forgot to ask. What temp should I expect the electric fan to come on?

Thanks Ingin

[junglejuice]

From the pic that is way too low, "normal" temp is around 96* which is just below half, the fan is supposed to come on at around 105* or just over half way.

Cheers, JJ

[ingin12]

With this in mind, I guess I should be looking at the thermostat. I see there are two available, 160 deg and 180 deg. I am not sure what mine has (if any) and the FSM does not suggest which should be used. Can anyone suggest the correct one?

Thanks Ingin

[junglejuice]

Normally a 195f thermostat is used.....

[rainman]

Normally a 195f thermostat is used.....

that is what mine is.

[ingin12]

Thanks Rainman, I am going to change the thermostat and the temp sensor, I will post the results when completed

Thanks again
Regards Ian

[EwenM]

correct JJ, on mine on a cold day you can watch the thermostat cycle open and closed

the gauge will go to half way then drop back then up to half and then drop a couple of times before stabilising once the motor reaches operating temp, its reassuring to know its all working as designed