Have a question about the cooling system on the 4.2L engine. I actually have an XJ8, but (no offense intended) the x350 section doesn't seem to have much technical discussion going on. In searching for similar issues, I found more results in this section.

I have a problem with the car not ever getting up to operating temp when the outside temp was < 40F. I drove the car 6 miles in 35F weather and the gauge never got to the 1st tick mark. When 50F or warmer, would get to normal temp eventually. Car was fine on Saturday, warmed up quickly, then Sunday it wouldn't warm up.

Would have bet anything on the thermostat stuck open.

2 days later I started getting wacky temp gauge operation--when I started the car in the morning (cold) the needle would go up to normal, then over 10-15 seconds fall back down to cold.

Took it to the dealer for repair (it's under warranty). Told him all the above info. He calls me back and says they're replacing the aux hvac water pump. Are these not just an ancillary pump to help the heater core? These don't help or hurt the normal engine cooling, right?

Then he tells me my coolant was very low--and I know for a fact it was filled to the top of the reservoir the day before. Now either it burped one very large bubble, or he's just giving me a bunch of BS. He also said the tstat was replaced last month for the previous owner.

Has anyone seen that kind of wierd gauge behavior? And does the aux water pump have anything to do with these issues?

Thanks very much for any help,
-Michael

 

I'd be more inclined to look that the thermostat for weird issues like that, but not sure about the hvac pump. The low coolant means a leaking coolant reservoir most likely.

 

That is exactly what I thought. I don't think this dealer is using common sense. I told him exactly what the symptoms were, they pull codes and see some "heater core temperature" error and replace the hvac pump. I had plenty of heat, it was just the engine not coming up to full temperature.

He said it's fixed now and everything is working correctly. He also said they pressure testd and found no leaks. I'll be picking it up this morning and find out, I guess...