Cooling system question

I have been poking around in my 1998 xj with the 4.0 today. Just to make sure that all is well mechanically and it wont need any more work before ordering a lift and I noticed something about the cooling system today that I wanted to run by here. So at the front of the engine we have the thermostat housing which houses a temperature sensor. This sensor I believe measures the temp of the coolant and sends it to the computer and only the computer. If this coolant was hot I assume it would go off? At the back we have in my case a flat green wire going from the head bolt you cant take out when removing the head and bolting into the wall behind the gauge cluster. This reads temps to the gauge only right?

So if cyl 1 was running hot and you pulled the plug 10 hrs after use to see it that red and white color that it usually is when an engine is running hot it would have definitely triggered a code because that coolant sensor is so close to cyl 1 that it would have to pick up something if it was having problems with temp correct?

I am just trying to understand how this system works

HO-up XJ CTS is both pcm and gauge.

Do you have a gauge or just the light? I'm not sure I totally understand what youre asking, but coolant is constantly flowing around the coolant temp sensor on the t stat housing because it's in line with the heater hose. It would never be able to pick up one cylinder running hotter than the rest.

I have an actual temp gauge not a light. But I also have that flat green wire going from the head bolt on the drivers side behind cylinder six to the wall right behind the gauge cluster. On my 99 its a black wire with a protective casing. If that is not a wire for the temp gauge then what is it. I doubt that the coolant temp would be used as the engine temp

The wire from the last head bolt to the firewall is a ground strap. Its used to keep the engine and body electrically connected and neutral.

jerms234 said:

The wire from the last head bolt to the firewall is a ground strap. Its used to keep the engine and body electrically connected and neutral.

Click to expand...

This. It's a ground strap.

Alright thank you. So the engine temp gauge reading the coolant temp from the thermostat housing then?

I think the 1996?-1999 heads are casting 0630 and the obd II computer started taking temperatures from the front sender, some early 0630 heads still have the port for the rear sender even though it wasn't used from that date on.

the older XJ have two one temp senders one for the gauge and one for the computer.
Layer years did away with the redundancy.


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