Is the HVAC water pump integral to the engine cooling? Or just a supplement for the climate control?

I brought my XJ8 to the dealer for warranty service because when ambient was below 40F the engine would take 10 miles to get up to normal operating temperature. I had heat, but the gauge never got much above the 1st major tick mark. Would have bet on the thermostat being stuck open or similar (as mentioned in another post).

2 days before I brought the car to the dealer, I starting getting wacky temperature gauge operation. When I went out to start it in the morning, the gauge would go up to the normal temp mark, then slowly (over 10 seconds) fall back to cold. I figured maybe something happened to the coolant temp sensor.

Find out today they're replacing the HVAC coolant pump, said they just did the thermostat for the previous owner a month ago. Also told me my coolant was very low (which I know for a fact it was filled to the top of the reservoir the day before I drove it to them).

I guess I can't complain, it's under warranty, but that makes no sense to me. I had heat, just didn't warm up fast enough. Dealer said maybe there was an air bubble trapped (which I could see happening).

Does any of that make sense? Could anyone share a diagram of the cooling circuit?

Thanks,
-Michael

 

I would like to see the HVAC water pump details as well. But it appears as if you may be loosing coolant or it was not properly filled to the top and purged after the thermostat was replaced. Erratic temperature readings can occur if the coolant is not full and sometimes it reads coolant temperature and other times it reads air temperature.

 

The air bubble makes the most sense... but the same dealer did the tstat replacement in December. You'd think he would have purged it correctly.

He said this time they did a pressure test, no leakage, just very low on coolant. When I get the car back I'm going to ask him how low, because I know it was filled to the top of the bottle and definitely did not have a "low coolant" warning.