Coolant Temp Sensor

I bought a 1997 XJ in the fall of last year. Then the head gasket blew with no indication from the temp gauge. Only after I shut off the vehicle and turned it back on did it read in the red. Got it all fixed and because of that issue I was going to place an additional sensor in the upper radiator hose with a second gauge in the cab. However, my buddy that fixed my head gasket told me my head has a second location in the rear and that the head must have been swapped at some point with an older model.

My question is can I use that location at the back of the head as a second coolant temp sensor like I would with the location in the radiator hose?

You could. The location on the rear of the head was the location of the coolant temp sending unit that ran the temp gauge on older XJs.

Yours uses the one in the thermostat housing to feed coolant temp to the PCM. The PCM then drives the temp gauge, electric fan and controls ignition and fuel injection.

The plug is likely secured with some very strong locktite (or similar) so it may be a bear getting it out.

A radiator hose inline adapter would be much easier to install and less risky.

Depending on where the head gasket blew, you would have other symptoms that may not include an overheat right away.

Saudade said:

You could. The location on the rear of the head was the location of the coolant temp sending unit that ran the temp gauge on older XJs.

Yours uses the one in the thermostat housing to feed coolant temp to the PCM. The PCM then drives the temp gauge, electric fan and controls ignition and fuel injection.

The plug is likely secured with some very strong locktite (or similar) so it may be a bear getting it out.

A radiator hose inline adapter would be much easier to install and less risky.

Depending on where the head gasket blew, you would have other symptoms that may not include an overheat right away.

Click to expand...

Thanks for the tips...new to all this stuff. Did not consider the plug and how well it would be secured. I will check it out on my weekend if its on there good not going to to force the issue and will go with the original inline adapter.

They make an alternative thermostat housing with an auxiliary temperature bung in it. The factory one at the back of the head is very small and tight quarters.