Poor heating

[Jag 1979]

My Daimler 1979 series 3 fuel injection has poor heating.

The temperature gauge sits just below the half way mark.

Im wondering, if the thermostat is not closing properly?

The Daimler does have A/C but I dont think that it works?

It looks hard to change my thermostat, as my engine is the early type.

When I adjust the temperature knob on the dash, I can here the valves opening and closing.

Does any one have any idea what sort of temp I should be getting at the pipes near the heater valve>

[mike020150]

Thermostats aren't difficult to change and should be regarded as regularly requiring replacement every 3/4 years. Start with a new thermostat and ensure the cooling system is bled fully when you refill the radiator. That way you will have eliminated the two most common reasons for a poor heater performance. To check another possible culprit, you should ensure that the heater valve on the engine bulkhead is moving between its extremes of fully open to fully closed as you move the temperature control from cold to hot. Mike.

[Jag 1979]

Hello Mike, thanks for your reply as always.

Mike, my thermostat housing is different on my Daimler than my later 1982 xj6. It look more complicated to get too.

Do you have any idea of the type of thermostat and gasket that I need?

I cant seem to find the correct part numbers?

Regards Karl

[mike020150]

The thermostat should be an 88 deg version (JLM9635) for vin number cars from 330299 without aircon and from 330666 with aircon to engine number 8L109004. Otherwise, 4.2 litre cars were fitted with 82 deg thermostats (JLM9634) from 8L109005. The gasket should be C28375. Mike.

[Jag 1979]

Thank you very much Mike....

[PaulGover]

Another regular cause is the vacuum-powered valve on the middle of the firewall at back of the engine bay, which can seize or suffer from damage to the vacuum pipe..

[Jag 1979]

Hello Paul, sorry for late reply.
Paul do you mean the heater Valve itself? (vacuum-powered valve).
My temperature gauge reads the correct themp and I'm also of the understanding the the heater valve is open.
So, therefore there should be heat?
Also, I would like to replace the vacuum pipe coming from the heater valve.
Do you know where I can buy this vacuum pipe?
And where is its starting point?