In a normal car when you drive you gradually get heat and after a couple of miles full blast from the heater.
But on my 97 jag you can drive 10 miles ,get no heat then leave the car for about an hour and when you start up instant heat . Any thoughts on this ? The pump is running and all pipes hot.

 

Following this thread. My 99 XK seems to have very little heat. I have only had the car for a few months and just tried the heater. Everything SEEMS to be working but very little heat coming out. Searching for answers.

 

My reply to another thread on heater issues. May work for you

"One thing you could try would be to unplug the electrical connector at the valve and see if that makes a difference. When i unplugged mine, it made a massive difference. When my temp is set at say 75deg, my 97 starts blowing warm air within a half mile from the house when cold, then gets nice and toasty, then after a few miles, the temp drops off. When i turn mine to high, itll make you open the windows, almost like standing too close to a bonfire! As i was told, when you unplug the connector the valve defaults to open so you'll have constant heat, and BOY DID IT WORK FOR ME! I think my issue is possibly my internal sensor, but try unplugging the heat valve and see what happens. Pretty easy to plug and unplug"

 

I went out yesterday and looked in the direction of the firewall, heater hoses, etc. There are several electrical connections and valves. Could you possible include a picture of the one you are talking about? I am not a mechanic but can follow directions...

 

Reasons for no heat are

Blocked heater core is very common ..take pipes off and fill with flush agent.
Heater pump not working ..access is very difficult.

Valve stuck closed ..defaults to open if disconnected. I assume the sensor below the steering wheel controls the valve so maybe the thermistor is faulty. ( temp rises resistance falls.....temp falls resistance rises )

 

This is the one to unplug. Just remember to plug it back in before using your A/C or you will get hot air

 

Thanks for that picture. Makes it much easier. Does this set off any codes by removing plug?

 

NO

 

No sir none at all

 

In the photos above if you pull the black plug which is the one to the pump motor and check the resistance across the plug pins you can check if the motor is ok ..if its reads open circuit the motor is buggered. a few ohms then its ok.
Am going to have a go at the thermistor behind the kick panel ...called the aspirator assembly ....a thermistor and a small fan .open circuit the thermistor will make it think its very cold ..easier to get at if it affects the air con in the summer

 

Is the thermistor the one at knee height behind the little grill? I opened that one up on mine the other day and it had lots of stuff covering the sensor. Heat seems more stable for me after cleaning it out

 

yes thats the one

 

The hose furthest to the right of the picture is bent at such an angle that the hose almost seems too flat for water to get through. I think I read that someone else had said that on this forum before but I can't find it again. Could that "folded, possibly blocked off" hose be the problem of poor heat? It looks like from the diagram of the hose/heater system that there could be a longer hose put into place that would not require such a sharp bent angle. What do you think?

 

I think its a trick of the camera, but ill try to remember to look at it in the morning. My heat works VERY well when its turned up to high, or when the plug is unplugged. Ive only driven 2 days since i cleaned out the temp sensor, but it seems to have made the temp stay more constant at lower temps

 

I have the same indifferent heating and am just looking into it. The above-mentioned hose in my car seems to have gone soft and partly collapsed, so I am guessing that may be (or may not be) at least part of the problem.

 

It is not the camera angle. I put my hand on the hose yesterday and it is almost folded in half. That has to be impeding the flow of water.

 

Hmmm. I looked at mine, which is what the pic was of this morning and it looked ok from the side, however i didn't try pushing on it really. It could be soft, and if so that would definitely be a possibility to look into

 

If you have heat only on "Hi" and when the water valve is disconnected, double check the external temperature reading on the A/C panel. If it shows something like 120 deg F, the sensor failed and you get no controlled heat in the cabin.

Best of luck, keep us posted.

 

That hose (or two hoses with a non-return valve in the middle) is moulded with the flattened section at the top:

 

Understood. All I am saying is, since most all of the XK's on this forum are, or have had heating issues, that "maybe" this closed off hose "could" be part of the issue??? If a different, longer hose was installed, would that help? I guess there is no way to know without actually installing such a hose.