Hi guys!

Well, just in time for the fridgid season my heater has failed. The inside fan works fine, but nothing but frosty air comes out. Simultaneously, my low coolant lite is on, and even jumping the connector won't extinguish it.

Somewhere in here I think I read something about the heater pump (and valves?) and the low coolant sensor being on the same circuit. Does anyone have any additional info on that. Is there a connector somewhere (other than at the reservoir) that might be the culprit?

As always - THANKS!

 

I was there a few weeks back, with, at best, lukewarm air. I did a bunch of research.

1. Check that the aux pump runs. There is fuse (15) in the engine compartment main box. There is a relay, too. Best is to replace the relay with a short wire so you can hear the pump run. It is very faint and is best heard with the engine off. This is a dedicated circuit in the new cars, no relation to the fog lights. If it does not run, these pump are fixable very cheaply with new brushes, apparently. Expensive when new, and a pain to get to.
2. Check the valve. Best is to disconnect the top connector as this valve defaults open. Not positive how to easily test better as the connector is hard to reach and the valve operates quietly. Expensive bugger too.
3. Check with a laser thermometer that hot water actually goes in the core.
4. Turns out it is sort of hard to determine which of the pump or valve is faulty for sure, so I went with the cheap stuff first. I ended up buying a cheap set of adapters and a clear hose to perform a core cleanup. Just flushed it with clean water from the hose. Did it in both directions. Used some leftover radiator cleaner for maybe 10 min, cold water. Result was DRAMATIC. I had lukewarm air in 30 sec of the engine running. With the needle barely halfway to "normal", hot air was coming out. Best $12 ever! I was pretty surprised as I have done several repairs involving cooling fluid and I never had any indication there was anything crusty or contaminated with anything. Heater core pipes looked new, with a light reddish coating, nothing write home about. I was very skeptical this flush would do anything right until the end.

Best of luck, keep us posted.

 

Wow. A flush was all you needed? That was a life (and buck) saver! I'm sure my situation is worse though. I've always had plenty of hot air coming out (even in the summer when on "vent" only). And then suddenly, ... nada. I'll do a flush anyway, just as a matter of course, and definitely because of your experience.

Do you happen to know what the number of fuse you mentioned is? Do happen to know the relay location? Both of those are "very" compelling possibilities.

Hmmm, ... you said the valve is normally open. If it got physically stuck there, that might explain my hot vent air in the summer. "And" if it went from stuck open to stuck closed that would certainly put the freeze on my winter driving. Although a stuck valve is kinda unlikely, as I drive my car much more than the typical XK8/R owner, ... but it "is" still a possibility

THANKS! - Jim

 

Those non obvious scenarios is what I was worried about, too. Valve stuck or pump not displacing fluid. The impeller of the pump is magnetically linked to the motor, so the motor can run, but it does not mean the fluid is moving for sure. First order of business is to determine if the pump is actually running.

If you pull relay R1, the conventional "30" and "87" terminals become visible on the fuse box. Just short 87 (motor side) with 30 (12V) and listen for the pump humming. Ignition does not even need to be on, if I remember correctly. Also, the pump fails with failed brushes, so open circuit. Check resistance of the pump (terminal 87) to the ground. Mine read a few Ohms, so operational.

 

Fabulous info. Thanks FMertz. I'm on the road now in another car ("with" heat!), but I'll jump the wires when I return and see what happens.