Heater Matrix

[wlynch]

Hello,

Had my car inspected by a mechanic today because no heat was coming through the cabin.
Was advised water pump, thermostat, heater control valve were all working fine, coolant heat temperature was also good, and cooling system circulating fine.

However coolant is not passing through heater matrix due to being blocked, possibly by sediment.
First of all is this a common problem, if so would like to know how you resolved this issue.

Thanks
Winston

[ptjs1]

Winston,

I've not heard of zero heat in the cabin because of sediment, but I guess it's possible? I would think that if you've got that much sediment in the heater matrix, then your whole cooling system needs a really good flush.

If it were me, and I really thought the problem was sediment rather than teh heater controls or water valve then I would flush the whole cooling system with a hosepipe. I'd then disconnect the feed and return hoses to the heater on the engine bay side and flush that separately before reconnecting and refilling the coolant system. Make sure you (or your mechanic) know how to fill and bleed the coolant system properly on an XJS v12 before you start.

Good luck

Paul

[davidr]

Winston - I would have thought that if there was that much sediment in your cooling system then your radiator would be clogged up as well.
As Paul says, the way forward is to flush your cooling system right through including back-flushing the radiator. Whilst you're doing this you can pull the hoses from your heater matrix and see if you can get any flow through that with a hose pipe. Take your heater valve off (we showed you that at Kemble?) and make sure that it's not stuck shut. It is possible for the arm to become detached so that although it appears to be moving its not actually attached so doesn't turn the valve round inside.
In my experience, it's much more common for the valve to fail than for the matrix to get blocked. The usual issue with the matrix is that it springs a leak (my own V12 did that so I changed it).
If the matrix does need to be changed then the good news is that it's easier to do on the later cars like yours because the pipes on the side can be detached. If you take the glovebox out on the passenger side then you get to it that way. Not too hard a job.
If you don't want to flush your cooling system then you can still detach the hoses to the heater matrix and check you heater valve and flush the matrix that way. This is quite a high point in the system so you won't lose much coolant if you plug the open hoses. Keep the radiator cap closed and that will help slow the coolant loss too.
I would want to be sure that the matrix was blocked before I went to the trouble of changing it.
Hope that helps

[oldtimer]

Winston,
Further to what Paul and David have suggested you could try running the engine until normal running temperature is achieved and then feeling the supply and return pipes under the bonnet at the bulkhead. Both pipes should be about the same temperature. I found that the temperature could be raised on both pipes but when the fans were switched on the heat from the return pipe diminished in seconds indicating a lack of flow. Sadly, this is exactly the situation that prevails with my motor today despite having had a new heater matrix in the workshop for years

In my case I changed the main radiator many years ago and cut the header tanks off for inspection. As you will know it is a cross flow radiator and I found the bottom tubes blocked solid and that contamination diminished as you worked towards the top. I reckon well over a third of the radiator effectiveness was lost. Not only that, the old radiator complete with it's contamination weighed a ton by comparison with the new replacement The problem with flushing or back flushing is that the flow will only pass through tubes that have some access and nothing happens with totally blocked tubes. In my opinion trying to flush the system is a fruitless waste of time although others may claim otherwise but I remain to be convinced.

Although I did not see the year of your vehicle it is possible that the main radiator has previously been replaced.

It should also be noted that the metal feed and return pipes fir up extensively.

In conclusion ,providing the water control valve is operating correctly only a heater matrix replacement will cure the problem.

I shall be very interested in your result as I shall need to follow the same course of action one day

Oldtimer

[wlynch]

Thank you all for your comments, I think a process of elimination is best way forward before making a decision of replacing heater matrix.

[oldtimer]

Winston,
Subsequent to the above, it never occurred to me to mention the use of a Infrared Thermometer with Laser Targeting.
I have not had need to use mine for a while, so yesterday I tried it out on my modern S Type.
When the trigger is applied two red spots appear on the target area and by moving the gun closer or pulling back the red spots will merge into one, at this stage the temperature can be read off the screen to the rear of the gun.

I started the engine and monitored the temperature from cold to full heat and the figures recorded were exactly as I would have expected. Interestingly the return pipe was nominally lower temperature than the delivery pipe indicating that the fans are transferring heat into the cabin. The beauty of this device is that providing you can see the required target area you can take a reading.

In your particular case removal of the passenger side panel will expose the end of the Heater Matrix allowing a temperature check of all the feed and return pipes which will allow you to assess the remedial action required. ( and either side of the hot coolant on/off valve )

I hope that helps

Oldtimer

[wlynch]

All,

I am posting an update.

Met recently Gary & Bill from AJC classics in Southampton really good guys who explained in detail what was wrong with my Jag in their opinion. They believe the problem is with a stuck "flap valve" inside the car behind the dash.

Heater matrix, including heater valve are working fine due to inlet/output pipes being both hot which suggests their is no blockage in cooling system within the engine.

Regards,
Winston

[davidr]

Hi Winston - that makes more sense than the heater matrix being blocked. You may be able to free up your flaps by a bit of gentle tapping. Maybe the motors aren't working. You can check by taking out the fuses for the blower motors (to eliminate their noise) and then turn the heater controls from full hot to full cold and listening for the flap motors.
Regards
David