I have a 97 XJ8 3.2 sport. My problem is that when the engine is up to
temperature, at best I can only get 'tepid' air blowing out from the cars
heater (it used to work great and would be blowing hot air as soon as the
engine was warm).
The engine thermostat is opening OK and I have flushed the matrix by
connecting a hosepipe so that I know that it is not blocked. There also
seems to be a hot supply to the matrix as the rubber feed pipe is hot when
the engine is up to temp.
The heater pump is turning as I can hear it ( with a screwdriver pressed to
it and the other end to my ear ) but I do not know how to confirm that it is
pumping or how crucial this is. I also do not know how to check the AC
Can anyone please advise on what it may be and how to check it as with
winter coming its a bit cold.
thanks in advance
I don't know if the 1997 is the same as my 1988, but when this happens on
the XJ40, it usually means that the flap in the blower distribution box is
not opening to blow the air over the heater matrix. Thus, you are only
getting tepid air. You need to get into the box and see if the flap is
After draining the system to put antifreeze in, it now only blows cold air.
Can anyone tell me how to check the correct operation of the heater water
pump and valve?
TIA (cos its getting cold outside)
No offence taken.
I did run it, and have run it for 3 days now - so no air and well burped.
I have a feeling that there is something wrong with the pump or one of the
valves but I don't know how to check them as manuals for this model aren't
available to my knowledge.
Anyone tell me how to chech that they are working OK?
the heater valve is an electronically adjusted unit. That valve is
located near the bulkhead on the left side of the car (US). Remove the
plastic panel(s) and you should see the heter hose running to and from
it. Or was it under the radiator expansion tank? It is possible that
it is stuck from debris dislodged from the coolant flush. Start your
car, turn on your heater, and lightly rap on it with the handle of a
screwdriver. Next step would the remove the valve and visually inspect
the waterway for debris and clean it.
I have not had to replace one so I dont have the knowledge to test the
electricals, but I am sure you can check for voltage. I believe the
valve needs replaced. In the meantime you can splice the lines, bypass
the valve, to get heat until the new valve is installed.
If you get the car to operating temp and put your hand on the return hose it
should be hot (set heat control to max heat and max air speed of course!).
If it is NOT hot (i.e. you can easily hold onto hose) there is a blockage in
the water works. If it is damn hot but you are still getting cold air,
sounds like heater box/electrics problems.
The temp of the hose should be either equal or slightly higher than that of
the top radiator hose when thermostat fully opened.
Hi all, thanks for the time you took with the replies, I appreciate it.
Anyway, I now have HEAT and its back to NORMAL!!
here's what I did, use at your risk.
Again, flushed the matrix by taking the water pipe of the heater water pump
(the matrix supply and comes off the side of the pump at 90 degees to he
pump) and fixed in a garden hose pipe. Removed the marix return water pipe
from the top of the valve which is located below the expansion bottle. Be
careful when disconnecting this as it is only short and you really do not
want it to come off or damage the connection to the matrix just inside the
bulkhead. Turn on water tap and flush. Reverse and repeat until you are
Removed water pump and took off from of pump (3 crosshead screws) removed
and cleaned silver water seal plate and impeller of scale. Greased impeller
spingle and contact point of plate with marine grease. Put it back together
There is a one way plastic flow valve just before the input to the pump. I
removed this and have temp replaced it with a short 15mm piece of copper
domestic water pipe in an attempt to temp increase pressure from the pump.
Put it all back together, refill cooling system but add cooling system flush
and ran andine with heater on full for 30 mins.
I dont think al least that the pump can deliver much pressure so removing
the one way vave helped circulate the coolant flush around the matrix. At
this point I started to get heat from the blower - hooray.
When I had heat, stop the engine and completely flush the system again,
engine and ALSO matrix again as above.
Put it back together and add coolant.
I will replace the one way valve in a week or sowhen I'm sure everything
else is working.
Hope his helps someone.
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