1998 X308 No heat from heater

I’ve suddenly noticed I’ve got no heat whatsoever from my heater. Fans work okay. Engine warms up normally and to normal temperature so can’t think it’s the thermostat. In any case even if the thermometer was stuck open or closed surely hot water should still get to the heater matrix. My feeling is that there is no hot water in the matrix but not sure how to check it. Has anyone got any ideas please?

There is a electrical water pump used to circulate water into the heater matrix. Most likely there’s an issue either with this, or the valve control assembly it’s connected to. This would prevent hot coolant from getting to the heater.

Dave

Thanks Dave. Any idea how I locate and access the water pump, and then check that it’s working. I can hear a very slight noise when I put the ignition on, and then turn the engine off so not sure whether that’s the pump that I’ve always heard.
Simon

Supercharged models have a pump you can hear as you describe

The heater pump is located below the coolant tank.
If your front fog lights don’t work it’s probably a fuse gone causing your heater issue, which in turn is caused by the alarm sounder failing

A different but similar car, my XJ12, stopped making heat due to a completely blocked heater matrix. I had to replace it then all was good.

Cheers,
Jeff.

I believe the pump is by the firewall behind the throttle body, near the coolant tank. I never had to do this replacement myself, I only kept an eye on the topic in case it ever happened to me. I no longer have my X308 XJR. It may require removing the throttle body to see (certainly will for replacement.)

If you take a nice long drive on the freeway at speed, and there’s heat, then it’s probably a bad heater pump. The pump provides extra circulation at low speeds and idle. At higher speeds the main water pump will provide enough flow to keep the heater matrix supplied.

If there’s no heat under any circumstances, but the car’s overall water temperature is fine (as you indicate) then it’s probably either a bad valve or a plugged heater matrix core. You can diagnose the valve by unplugging it. I believe the normal state of the valve is open, so unplugging it would let hot coolant flow freely and you’d have heat at all times.

If that doesn’t help, then it likely is a plugged heater core and I believe that’s a pretty big project to tackle. But I don’t think this is very common unless mismatched coolant was used or some leak plugging additive was poured in.

(correction from "no heat" to “heat” above.)

Dave

I did wonder whether if it was the heater pump hot water should still get to the heater matrix due to convection. But I don’t know exactly how it works: for example if the heater pump turbines aren’t spinning then maybe that provides enough blockage for no hot water to get through. I suppose if you can identify the heater pump, feel the pipes in and out, and the in one is hot but the out one is cold then it must be that. I doubt it’s a blocked matrix as it’s never had mismatched coolants and it’s quite clean.

I see bad wording in what I wrote before. Instead of “no heat” it should read “heat.

My understanding is that at low speed, the water pump often cannot generate enough flow to supply the heater core. So the heater pump kicks in to provide flow at idle/low speed. No heat at idle but heat at speed suggests a bad pump.

The heater pump will run even with a frozen impeller, because it drives the impeller with a magnetic coupling.

Sorry about the miswording,

Dave

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Why do some people think the heater pump fuse is shared with the front fog lights one? I’ve looked in the JTIS manual and it shows the front fog lamps fuse as being fuse number 15 in the engine bay fuse box, but doesn’t show the heater pump against this fuse? I can’t find the heater pump fuse anywhere in this manual!

Correction: It’s fuse #17 for the front fog lamps.
It does say fuse #15 is “air conditioning coolant pumo” so could this be the heating pump, although I would imagine there is a separate pump to pump the air conditioning liquid/gas around that system which would be different.

“Air conditioning pump” is a Jaguarism for heater coolant pump. If you look at the parts diagram for a X308 Jaguar, you’ll see this. I recommend going to a vendor like SNG Barratt to look up this part and the diagram showing it.

The pump is powered by #15, but the relay that controls the pump is shared off the circuit powered by #3 (which also powers the fog lamps.) You have to look at the wiring diagram to see this. The owner’s manual doesn’t mention the coolant pump relay. Of course, if the relay doesn’t work then the pump won’t either.

Dave

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The pump is the same one as used on the X300 AJ16 with a different mounting, can’t remember where it is on the X308 usually it is the brushes that have worn down.
It is about an hours work to remove it (you only loose an egg cupful amount of coolant on the X300).
See:

According to the JTIS electrical wiring section and the electrical section, the pump is relay #1 and the front fog lights is relay #2, both in the engine bay main fuse box. I’m not sure the brushes would be worn as it’s done 79,000 miles and they seem to be worn at 120,000 miles. I’ll take it for a blast down the motorway and see if I get heat which would then indicate it is the pump I think!

brushes do not necessary last the life of the car.

Rather than argueing, do you front fogs work or not? lol

I have had two heater issues with X-300s - one was the pump and one was a blocked matrix. Both were painful to diagnose! I believe the only real method involves a couple of hoses, a bucket, and blowing through the hoses. If you don’t understand what the means, you should probably get someone else to fix this!