I have a 1999 XK8 conv, and have been having some trouble with the heater. Tried an few things that didn't work and now I'm looking for any ideas on what to try next.

Problem: My drive to work consists of about a five minute drive on city streets, followed by a 10 minute run up the freeway, followed by another 5 minutes of stop'n'go city street driving. On startup, heater works normally (kicking in after the engine warms up, of course). I stop, I go, I stop, I go, everything is fine. Hit the freeway, everything is fine. Then, I get off the freeway, come to a stop at the light at the end of the offramp, a few seconds later there is a whhrrrrrrump noise from the engine compartment (sounds like is directly ahed of the driver, near the firewall), a whiff of coolant-y smell, and in short order, no more heat. Ever. Until the car cools down and I drive home (where I get the same experience).

My first hope was that there was some air caught is the system, so I tried pulling the cap on the tank and "burping" the main radiator lines. I tried this with the car cold, and also let the car warm up (with the cap off) and tried it once I got heat coming out of the vents. No luck.

Well, putting optimism behind me, I had to admit that it really sounded like an issue with the heater's water valve. So, I bought a "new" used valve off the internet and replaced the old one. That didn't work either.

Searched the forums, but didn't come up with any more thoughts. So, I'm out of ideas. I suppose it is possible that the new used valve has the same problem as the old used valve. Anyone know how to bench check the valve (either the old old one, or the new old one)? Any other thoughts on what might be causing this?

 

Best bet would be the heater pump. In this car, the belt-driven water pump is supplemented by an auxiliary electrical pump to circulate the colant. It is a known failure point. Apparently, the brushes wear out, make noise/burnt smells, then cease to function. There have been several recent posts about this including an excellent step-by-step on the repair.

 

Perhaps, though I am not sure that the problem that I am having is consistent with that failure. The heater will work just fine on startup, day after day, and will run forever, until such time as the car has a) fully warmed up and b) been brought to a full stop for a few seconds (such as at a stoplight). I would think a conked out motor would not be so consistent and repeatable. (Though I am totally open to finding out if I am wrong in my thinking)

 

If you smell a whiff of coolant, there is a leak somewhere in the system. You should pressure test it if you cannot find visual evidence.

 

My sense is that you could be reaching the very end of the brushes on that motor, so it works as long as it is cooled by airflow, but seizes when it becomes hot (no longer moving, at a light, or in traffic). Just a thought, tough to be sure.

Do you have to top off the coolant once in a while (indicating a leak)? The thing is that the area that you describe the noise is coming from is the general area of that pump (top of the transmission, near the firewall). I guess a leak and a bad pump are possibly unrelated issues.

There is an excellent write-up here: Heater Pump Removal

See if this helps you convince yourself one way or the other.

Another option I can think of: Is there an issue with the heating system internal doors/flaps? Is the whirring noise you are hearing the same as when you hit the re-circulation button? Also, some folk have reported issues with the external temperature sensor circuit. When the temp is WAY off, the automatic temperature control fails to properly adjust. You can press and hold the external temp button to see the reading.

Best of luck, keep us posted.