In June I've changed thermostat, and the car was running good until December. Now sometimes it works on proper temperature, sometimes not. Sometimes temp gauge goes from the middle to zero (fully cold engine) in 10 secs, then it goes back while im driving. Most of the time temp is about 5 mm lower that it should be. The car is running rich, sometimes having trouble to start in this cases. Is it faulty thermostat again?

 

While this could be the thermostat ( usually fail open) the temperature sensor affects the fueling .Make sure you get the right one as some suppliers confuse a fuel temp sensor with the water temp sensor

 

I was having weird readings on the temperature gauge and it was the coolant temperature sensor.

 

Consider the OEM Temp Sender is probably original, suggest you replace it . The thermostat, being new, should not be defective so soon. If you have access to a infrared heat check the thermostat housing for the temp after engine reaches operating temp. Then look at your gauge for its reading. The gun and gauge should be very close.

 

Keep in mind that the dashboard temperature gauge is NOT an exactly correct indicator of engine temperature. Apparently it is designed to track the engine temperature from startup to normal operating temp. But then, when the normal operating temperature is reached, the needle "freezes" at the straight up position, so that normal (small) variations in engine temperature are not shown --- the needle stays exactly straight up. However, if significant overheating develops, I assume that the needle will "unstick" from the straight up position, and move up. Many owners might never see this happen (I haven't).

Also, this engine can be very slow warming up in very cold conditions (well below freezing). Normal operating temperature (needle straight up) may never be seen on short trips when freeway speeds are not achieved.

It seems possible that what you are seeing could be due to a fault in the gauge itself, of its circuitry.

Bob Frisby
1999 XK8
Boise, Idaho

 

Is the car fitted with a 'REAL-GAUGE' setup from jagwrangler?

 

this ^^^^^

alternatively, you can measure actual engine temp with an OBD-2 reader or one of the aftermarket gauges that plugs into the OBD-2 port.





Z

 

UPDATE:

I was sitting in the traffic jam, hearing some noises. Then when I moved along the temp gauge went to the red line, and the engine boiled. Mechanic told me that I was missing 5 litres of coolant, and after he changed a coolant cap he said that the car started to work good and each working temperature. (So my coolant level sensor is broken). The car is able to hit the middle of the gauge and good fuel milage only while randomly cursing along the town, sometimes. Neve on highway though
I don't think it is the gauge problem as I experience like 40l/100km fuel milage.
I don't have a real gauge, it is a stock one
My guess is the coolant temp sensor, but I am not sure

 

I am trying to order a new thermostat, and just not sure if I've found the correct one. Opening temperature is 83c? Are XK8/XKR thermostats are the same? Are 4.0, later 4.0 and 4.2 are the same?

 

I would recommend asking the mechanic where the missing 5 quarts of coolant went ?

That’s about 50% of the coolant capacity. It should be of supreme importance to trace how and where that much coolant disappeared.

If you don’t solve that mystery it’s likely to happen again.


Z

 

I asked to check if the coolant is still leaking, and there is no leak now. Seems like it got out through the second expansion tank when it was boiling. The car is still having trouble to heat up, and it boiled yesterday again. The coolant level was okay. Thermostat seem to work fine, I thought it is stuck, but apparently it closes and opens as it should. Maybe faulty water pump is the problem…
the car is fitted with k&n air filter, but I’ve never heard that it can affect the engine temp

 

The original Head Gaskets on the early AJV8 engines were fiber composite but later the design was replaced with MLS. (multi-layer-steel)

Both of my 2000MY XKRs have had their 'failed' composite head gaskets replaced with MLS years ago.(just a guess)

 

The water pumps on these cars don't last forever. The vanes on the earlier ones will disintegrate over time. I'm not sure about the XKR, but, on the XK8 they are not difficult to replace and not too costly. I'm sure there is a write-up somewhere on here about replacing one on an XKR.