I've noticed that the electric fan doesn't switch on when the engine reaches hot temperatures. It however will kick on when any of the A/C or defrost modes are selected. My scan tool measures the temperature at 223 after idling in city traffic, no fan kicked on?

Could anyone point me towards a solution for this?

 

Which XJ are you talking about, the '96 or the '98?

 

Sorry, this is for the 1998.

 

What does the instrument cluster temp gauge read when it gets 'hot'?


After the engine has cooled overnight (Do not start the engine) remove the radiator cap and measure the coolant temp with a digital thermometer and compare it to your scan tool reading. Is your scan tool reading properly?


When cold, as above, use your scan tool to check the ECT temp against the IAT temp. The two should read within 6*F of each other.


The fan should turn on when the coolant temp reaches around 218*F, and turn off when it drops to around 209*F.

 

The instrument guage measurement seems to be almost identical to the scan tool. Both guages show accurate, at least based on when the thermostat opens up. Water pump and thermostat replaced last weekend, electric fan was not working prior to that repair.

Thanks for the tips regarding the digital thermometer and the IAT/Engine temp. I will check them tomorrow morning.

 

CCKen,

This mornings measurement confirms the scantool as good. Both thermometers measured at 52 degrees, and the IAT measured 54 degrees.

 

It looks like your scanner is working okay.


A simple test of the ECT/PCM/Fan function is to remove the connector from the ECT and start the engine. If the Fan starts, the over temp function is working. If it doesn't turn on, there is a defect in the circuit. This will trigger a CEL/DTC but it can be cleared.


Try it.

 

Does the ECT send the temp reading to the guage, or is the block sensor responsible for that?

 

The ECT sensor on the thermostat housing sends signals to the PCM via the CCD Bus, where the instrument cluster microprocessor converts the CCD Bus data to data that drives the temp indicator, and the PCM uses this same CCD Bus data to determine if the coolant temp has reached/exceeded the trip point to turn on the fan. The CCD Bus also makes this data available at the Data Link Connector so you can see it on your scanner.


The '98 doesn't have a block sensor like your '96.

 

Removing the connector from the ECT and starting the engine also starts the fan. Could something else be causing the fan to not kick on at high temps?

 

The PCM aside....


Replace the ECT. Use a good one like an OEM or, at minimum, an Echlin from NAPA.

 

Thanks CCKen. I'll look into that.

I hope all Michigan's snow has melted away. I lived in Grand Rapids for 25 years before the grey slush forced me out!

 

After re-reading your original post it looks like you will need a new fan clutch if your temp gets hot while idling in city traffic.


I recommend the NAPA fan clutch part number 272318. I bought one several weeks ago and it works fine. It's made in the USA.