To start off I'm suspecting a bad thermostat, but I have a couple questions.

First of all I drove the car to work today and the temp didn't get past the 1/4 mark on the gauge until I turned the heat off on an 8 mile trip, but I noticed when I changed the coolant out recently with the heat on and the car off it cycles coolant through the heater cores even when the car is not fully warmed up. Should it do this? Shouldn't the thermostat limit the coolant flow until warmed up?

I'm really concerned much more time and the CEL would have set for not making it to operating temperature. Total drive time was 15 minutes. The heat was nice and warm the whole drive. I don't suspect the sensor because I opened the bleeder on the expansion tank in case an air bubble was causing it to read low since the sensor needs coolant contact for an accurate reading. It took a bit to get coolant out (2-3 seconds) so it might have been an issue, but the coolant didn't feel burning hot like I've come to expect from a running warmed up car.

 

Also can I just replace the thermostat on this car or does it require replacing the whole housing?

 

It is likely you had/have air in the system.


When the engine is started and the t/stat is closed, the water pump circulates water through the engine into the upper hose and back to the water pump. When the t/stat opens the coolant flows through the upper hose into the radiator and then back to the water pump through the lower hose. The coolant flow to the heater core is a parallel circuit and flow of coolant is independent of the t/stat position.


Heater core temperature should slowly increase as the engine temperature increases and then level out at the normal running temperature.

 

Either. But remember that the plastic t/stat housing ages and can crack.

 

Yeah, I definitely was able to bleed some air out of the system but it's been weeks since I did the coolant change. I'm surprised I haven't had a problem sooner then. I'm not all convinced it's fixed just yet though. I haven't driven it again yet. I did remove the engine cover and the T-stat housing isn't leaking, but I do know there could be issues internally. I'm tempted to just swap the thermostat as it's so simple, but the common sense side of me is to replace the whole housing if the t-stat is actually bad.

 

Ok, now after driving the car it seems fine. Once it gets to temperature it maintains temperature and does not drop from operating temperature even on the highway with the heat on full blast. Since the heater cores are in the loop with the engine, is it possible if I leave the heat on high while the car is warming up does that dramatically slow the warm up time? Something tells me Jaguar would have thought of this or there's an issue with my car. Should I only use the auto function for the climate control. Am I over thinking this?

 

My car is usually up to temperature in about 2-3 miles in 50F weather. I wouldn't expect the heat setting to affect warm up time too much---there is full flow of water through the heater core all the time regardless of heat setting.


You can check the heater feed and return lines and you will not feel much diiference in temperature.(at least my thick skinned hands don't!)

 

It must have been the air bubbles. I can't figure out what the problem was otherwise.

 

Some people have had difficulty bleeding the coolant system on these cars but

have been successful when the car is parked on a fairly steep slope.

 

Yeah it was 30 here this morning. I was up to temp quick this afternoon though.