2001 S-Type 4.0 (w/120,000 miles) –

My car’s heater will eventually put out pretty good heat. But with AC engaged (to control fogging), it's pretty anemic and never gets much beyond luke warm. On a long drive and with the seat warmers on, the cabin will eventually be comfortable on a cold day. But my 8-mile drive to work is rarely enough!

Details:
· The car reaches normal operating temp within a mile or two of driving and then remains right in the middle of the temp gauge.
· At higher RPMs, the air temp gets significantly warmer, although the temp gauge doesn't change. So any time spent idling at a stop light, especially with AC selected, can be a bit chilly!
· I have bled air from the coolant system (per tech manual instructions) with no apparent impact. There wasn’t much air to bleed.
· The coolant appears clean and fresh. No oily residue, rust, etc.

Three thoughts:
· I could have the coolant system flushed. But since the coolant seems so clean, I wonder if a heater core blockage is unlikely to be the problem and if flushing is worth the cost?
· I understand that this car has an auxiliary heater pump, but I’m not sure how to check its operation or whether this is even a likely culprit.
· I wonder if the water pump impeller is worn and not moving coolant efficiently. But the car never overheats, even on the hottest summer day in Texas.

I didn’t pay a lot for this car and I’ve only owned it for a little less than 2 years. I’d love to avoid an expensive fishing expedition at a dealer, so any suggestions/advice would be greatly appreciated…thanks!

 

If it's any consolation, my '02 V6 takes about 8 miles before the heater really seems to crank out the heat.

The RPM based symptoms? That points to the auxiliary coolant pump, only used on the V8 models. I'm not entirely sure how to check it, other than to carefully touch the pump at idle and see if you can feel it running.

More details here, specifically the troubleshooting steps in posts #2, 3, and 6:


https://www.jaguarforums.com/forum/s...ol-how-185002/


Be aware the temperature gauge is deliberately misleading. There's a link in post #6.

Also, try putting the system in manual mode by driving the temperature up until HI is displayed. This bypasses some of the automatic features and is very helpful for troubleshooting. However, it seems your aux pump is the most likely culprit. Don't just rush out and replace it, but check first if it is running at idle with HI displayed.

 

Thanks for your quick reply, my friend! I'll take a closer look at the post you noted and see what I can find. I appreciate you!