XJ XJ6 / XJR6 ( X300 ) 1995-1997

Lazy heater

Old 04-27-2019, 09:31 PM
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Default Lazy heater

Apologies in advance if this has been covered before, but I used the search function and couldn’t find it...
My XJR heater works, but it’s not what you’d call ‘impressive’.
it is hotter when I have been grunting it, but when cruising in traffic, it doesn’t pump much heat.
I presume the small electric motor on the left side of the engine bay is the pump for the heater water - is that correct? If so, do they get sluggish and could it improve if I replaced the pump, or is this just life with a 22 year old Jag?
Old 04-28-2019, 03:11 AM
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Getting COLD across the ditch also, I reckon.

Both mine were sluggish heaters, until I replaced the thermostats, and pressure caps.

My best understanding???????, is that little hose pump only kicks in when HOT is demanded from the system, and the interior is COLD, BUT, I will stand corrected on that.
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Old 04-28-2019, 03:21 AM
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The pump itself is pretty awful on these cars, I'm surprised you didn't replace/fix yours yet? Brushes on these will usually last only to just over 100k miles and the pump will stop. Propeller in the pump normally grinds a small groove in the metal base and that may slow down its operation and impact heating when the sides start to rub on the base. Next time it fails on mine I'm planning to replace it with a webasto pump or something similar.
Other than that there are three more things that may affect your heating.
1. Heater valve which sits pretty much next to the pump.
2. This is in part controlled by a temp sensor that sits just under your steering wheel and gets easily clogged with dirt which impacts its operation.
3. Partially blocked heater matrix. I flushed my system by first running the car with a rad flush for a few days then repeatedly filling it up with water and running the car with the heating fully on(and until hot) and then draining it down. It took 20 cycles before I finally got clear water running in the system. Heater matrix operation was also greatly improved. Ideally though next time I'll attempt something like this, I'll connect both ends of heater matrix to a container with some stronger chemicals and an electric pump in a circuit and flush it properly.

Last edited by katar83; 04-28-2019 at 03:26 AM.
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Old 04-28-2019, 10:31 AM
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From my own experiences, and what I've heard from others, I wouldn't get my hopes up too high. Under the best of circumstances, with everything known to be in proper working order, the heating system seems to be a bit weak on the X300s. Nowhere near as strong as, let's say, my Series III Jags.....or my Ford truck, nor my old Honda.

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Old 05-04-2019, 04:58 PM
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I had to use heating today and checked mine at full heat so to give you a good indication at how it should operate, at 'HI' setting and at ~3/4 full which is probably the hottest you can get it, if you direct the center vent at the steering wheel, you should not be able to keep your hand at the steering wheel for longer than 20-30sec as the air is uncomfortably hot, mine is definitely too hot.
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Old 05-06-2019, 03:44 AM
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Thanks for all the above replies.
i ran the heater at full today, 10’C outside, vaguely warm.
it only felt hot on my hands with it on recirculate after a burst of full throttle -the full throttle seems to make a real difference. Clearly not working as well as when new in a previous millennium!
Old 05-06-2019, 07:21 AM
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Plenty written here, on it. Basically, confirm yourT-stat is not sticking open. Confirm your heater pump and water-valve are working; If that doesn't do it, you'll need to back-flush your heater core. 20 minutes or so with the proper garden-hose adapters.

It should be capable of making you most uncomfortable, even if ambient is well below 0 deg C.
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