Had the car going the other day and noticed the heater was
only blowing out lukewarm air, even though the engine was
fully warmed up. It was a cold day and with the temp setting
knob set where it was (maximum), it ought to have been
blowing fully hot.
I wondered if anyone had experience of such a problem? I’m
reluctant to start pulling the dash to bits if there’s a
common fault which can cause this.
Also, is there any test mode for this delanair mkIII system?
My previous XJS had the earlier delanair, in which you could
hear the servo whirring, quite a handy sign showing the
controls were working.
Many thanks, Bill–
1989 XJS V12, 1994 Landrover Discovery, 1972 Rover P6 2000TC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
// please trim quoted text to context only
Ptipon
(Ptipon, Sonora, CA, USA, 1990 XJS, Conv.)
2
In reply to a message from BillLM sent Tue 26 Jan 2010:
I did and I have now come to realize that phenomena could also be low coolant.
In my case I had no heat at all but didn’t worry about it because it was with the top down, driving at night that I would
use the heater. I thought I would go after that problem when the weather required that I do.
Well it cost me my first dropped valve seat. Much later I found that I had a bad coolant level sensor and was not
getting this warning at all. The engine never showed overheating but obviously had hot spots at the top of the heads
where no coolant was circulating. Now I make sure that I know my cooling system is completely full with no air. I have
placed a clear, cord armored hose from the catchment tank to the atmospheric tank. With just a glance I know I have max
coolant and that the siphon is set-up and operating. This is impossible to determine with the opaque rubber black hose.–
The original message included these comments:
I wondered if anyone had experience of such a problem? I’m
reluctant to start pulling the dash to bits if there’s a
common fault which can cause this.
In reply to a message from Ptipon sent Tue 26 Jan 2010:
I too have had low coolant level stop the heater working, on
other cars.
However, I don’t believe the coolant is low on this car, if
the levels in the two tanks are anything to go by.
It seems very slow to warm up too, although perhaps thats
normal, I don’t know. The 6 cylinder XJS I had came up to
temp fairly quickly, but thats a far more modern design of
engine than this V12.–
1989 XJS V12, 1994 Landrover Discovery, 1972 Rover P6 2000TC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
Your coolant levels may be OK but you might have air in the coolant
system. Have you properly bled the air from your coolant system?
BTW, exactly where does the temperature gage read when your car was
“fully warmed up”?
Have you checked that your heater valve appears to open and close
fully when you change the temperature setting from full heat to full
cool?
Regards,
Paul M. Novak
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1985 XJ6 Vanden Plas (parts)
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA @Paul_M_Novak1On Tue, Jan 26, 2010 at 3:43 PM, BillLM landy.man@live.com wrote:
In reply to a message from Ptipon sent Tue 26 Jan 2010:
I too have had low coolant level stop the heater working, on
other cars.
However, I don’t believe the coolant is low on this car, if
the levels in the two tanks are anything to go by.
It seems very slow to warm up too, although perhaps thats
normal, I don’t know. The 6 cylinder XJS I had came up to
temp fairly quickly, but thats a far more modern design of
engine than this V12.
It should be warm enough to give some heating after driving 2-3 miles.
Perhaps the heater valve isn’t working. It’s on the right side on the
firewall. Aftermarket units are available at most auto parts stores and easy
to install. Try to feel the hose near the valve and compare it to another
hose, e.g, one of the upper radiator hoses. If it’s cool either the valve is
shot or it’s not seeing the vacuum to open it. I don’t recall the exact
procedure for testing it, but I’ve seen it described here. If someone
doesn’t jump in with it, do an Archive search on “heater valve”
In reply to a message from Ed Sowell sent Tue 26 Jan 2010:
Many thanks for the helpful replies.
I’m sure the engine is up to temperature. The gauge sits a
little under halfway once its all warmed up. The radiator
hoses are hot, but it sounds like I need to locate this
valve as it sounds a likely culprit. I suppose for a
temporary job I could always bypass it with a bit of pipe.–
The original message included these comments:
Perhaps the heater valve isn’t working. It’s on the right side on the
firewall. Aftermarket units are available at most auto parts stores and easy
I’m sure the engine is up to temperature. The gauge sits a
little under halfway once its all warmed up. The radiator
hoses are hot, but it sounds like I need to locate this
valve as it sounds a likely culprit. I suppose for a
temporary job I could always bypass it with a bit of pipe.
Not sure what you mean by halfway. If it’s halfway between C and N it’s too
low. Either you have the wrong t’stats or the gauge is off. It should be a
little under N. Probably not causing the heater problem though.
The aftermarket valves are so inexpensive and easily available that it
wouldn’t make sense (to me anyway) to bypass it. The hardware to do the
bypass would cost more than a valve.
To find the valve follow the 5/8" heater hose as it leaves the upper right
rear side of the engine. The valve is at the other end of it. If it’s the OE
valve it will be bolted to the firewall to the right of center. TO work on
it you will probably have to unbolt the wing cross-brace from the cowl.
Yes, you are correct. Vacuum is applied to open the valve. With a
loss of vacuum the valve closes.
If you get in just the right position with the engine running and
watch the valve while someone manipulates the temperature switch from
full cold to full warm with the climate control system on, you should
be able to see the valve open and close.
Regards,
Paul M. Novak
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1985 XJ6 Vanden Plas (parts)
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA @Paul_M_Novak1On Wed, Jan 27, 2010 at 2:54 PM, BillLM landy.man@live.com wrote:
In reply to a message from Ed Sowell sent Wed 27 Jan 2010:
By half way, I mean half of the gauges total travel. So yes,
the needle is just below the N.
Would I be right in thinking the valve closes when vacuum is
applied?
–
The original message included these comments:
Not sure what you mean by halfway. If it’s halfway between C and N it’s too
low. Either you have the wrong t’stats or the gauge is off. It should be a
In reply to a message from BillLM sent Tue 26 Jan 2010:
I finally got this heater probem sorted.
Bulkhead valve was fine as the pipes to the matrix were
getting good and (scalding) hot.
Further investigation revealed it wasn’t going into defrost
mode either, despite the vacuum actuator moving. It turned
out neither the upper nor lower air distribution servos were
moving. Fans were working OK.
Testing servos with a battery, upper worked, lower was dead.
Removed lower servo, dismantled and the brushes were stuck
in the motor. Freed them up and reassembled. Now everything
works fine, including the upper servo.
Its curious how failure of the lower servo stopped the upper
one moving. I can only conclude that the ECU only starts to
move the upper one, once the lower servo has reached a
certain position.
Had the car going the other day and noticed the heater was
only blowing out lukewarm air, even though the engine was
fully warmed up. It was a cold day and with the temp setting
knob set where it was (maximum), it ought to have been
blowing fully hot.