Let there be heat!
I finally buttoned up the rest of the car, started, let run to operating temp, and now I have heat! SUCCESS!! It was the auxiliary pump.

 

To resurrect this useful thread, I have a symptom and a problem.

My 2002 XK8 heater works, but it works poorly when highway cruising and much better around town. Specifically, on the highway at 70-80mph with the heat cranked up to Hi it gets warmish, but never hot. Around town, at Hi it does get much hotter but never unbearably so.

I had been inclining towards the thermostat being stuck open - thinking of the coolant being overcooled at speed but warming up in town. I wasn't aware these cars had an auxiliary heater pump - but I am now.

So could it be the pump or am I right about the 'stat? Opinions?

 

Thermostat problems seem to be common, so changing it is not a bad idea. If you still have the plastic housing you should consider changing to aluminum, as it may break when changing the 'stat.
If that does not solve the problem it is probably due to a partially plugged heater core. Many members have backflushed the core with good results.

 

It may also have a partially open check valve (or two) in the 'octopus' hose, or someone may have replaced one (or both) with a straight-thru nipple(s).

 

I fixed the no heat problem on my 2006 XKR coupe after replacing the heater valve and heater pump to no avail.
I looked at the U shaped hose from the heater outlet on the firewall. It bends so tight that it crimps itself. I places a 10mm inside diameter extension spring about 100mm long inside the hose.
I had plenty of heat immediately! The heater core never got this hot before an made some new cook off smell for the next our of driving. No I have a good winter car.

 

Thanks for important information!

 

This one?




The kink is supposedly by design, but it is hard to imagine the design is original. It feel like the one-way valve was put in there after realizing there was convection into the heater core due to the proximity with the cat converter once the car was shut off. I have thought before that maybe this valve (reversed!) could be put on the supply side as there is a lot more length of hose to work with. This hose would then have to be reworked to simply be the union of two 90 deg sections. Fortunately, this hose is easy to reach and work with once the overflow tank is out of the way.

Can you share a picture of the kind of spring you used for this mod? Thanks.