Dear All,

Where do I start? Had my right front wing replaced a few weeks ago, my RHS indicator sometimes flashes fast, but when I check it flashes normally. Now my heater in the cabin doesn't seem to work. There are no faults reported.

The temp display all works, so where do I start? It's a 2003 4.2 XK8.

Mike

 

Usually a quick flashing indicator means a blown or faulty indicator bulb or connection ,when this as happened to me I just changed the bulb😊

 

Check the RHS indicator repeater bulb. The wiring must have been disturbed if you've had the wing replaced.
If these blow (I'm assuming here that the later cars are the same), the indicators flash at the normal rate, but the audible tick alert is at double speed. I tried to replace mine with some yellow LEDs but the BPM must also have them in its custody

Heat: - are the blowers not working or does the cabin just not get warm?

 

Thanks for the heads up Graham. MichaelH,
Blowers are working, but cold air only. Temp gauge works okay, A/C seems to be okay. Fuses on RHS all good, no codes. So it's somewhere in the engine bay I guess. So are we looking at the Water valve do you think?
The indicator seems to be front flasher which is dodgy, probably the earth or the bulb, but I'll check that out with my meter.

 

 

Thanks Bones, Fog lights okay, but will check fuse 15 and R1 relay. Noticed slight warm output when car had been left for while. Is the valve open with no power? and do you need the pump to work before you get any heating?
Mike

 

 

The wiring is different in the 4.2. Trust the electrical diagrams on jagrepair.com

First, check the external temp sensor. If that temps have no relation to reality (e.g. 120 deg F), it needs to be changed.

To further debug, you need to use the front panel and put the temp to "HI". I believe this avoid any type of sensor feedback (cabin temp, solar sensor, aspirator) to best zero in on the problem.

If you get heat on HI, then it is likely a sensor problem.

Fuse 15 in the engine compartment fuse box drives the heater pump. Relay R1 drives the circuit from the ECU.

First, check the resistance of the circuit (fuse 15 to ground). The usual pump failure mode is brushes worn out, so "infinite" resistance. If so, you can repair the pump by getting cheap new brushes. These pumps are pricey.

Next, with the engine off, you can short the relay with a double bladed wire. Once you remove relay R1, the usual numbering for a relay shows up. Short slot 30 with 87 (30 is 12V). You should then hear the pump, but it is pretty faint. If the pump runs, the pump electrical motor runs. It is a magnetic coupling with the impeller, so this is not proof of water flow as the impeller could still be stuck...

My understanding is that no power to the valve means valve is OPEN. So drive the car with that plug off (the white one) and see if there is any heat. Valve can be stuck closed, or partially open, I suppose. These are even more expensive so it is hard to throw parts at this problem!

Next, get a cheap "laser" thermometer and check temps on all these hoses for more clues. Supply is the bottom pair of hoses, return is the top pair. The attached write-up (not mine) is GREAT to figure this out. You can of course feel the heat of the hoses in and out of the heater core for more clues.

And, this is where I am with my own car as well. Heater core supply hose is lukewarm, hence no heat inside...

Next is probably to try and figure out if there is flow. A plugged heater core comes to mind. Should be pretty straightforward to remove the heater core hoses and back flush with fresh water off a hose. Once off, the flow of the pump can be checked, too by briefly powering it on and collect the coolant coming out...

Best of luck, keep us posted.

 

So, I did this radiator back-flush procedure last night. Bought 10' of 5/8 clear vinyl tubing and a garden hose barb adapter. After putting the expansion tank out of the way for better access, I removed the 2 hoses to the core (sort of by the brake booster). I then hooked up the clear tubing so the house water supply would go up the outlet (reverse flow) and the intake would go to a collection bucket.

First off, I was pretty skeptical. I have replaced the water pump and radiator before and I have no indication this car's cooling system was ever contaminated with the green stuff. Everything is orange, no crusty/scaly stuff anywhere, no big debris coming out. So, upon removing the heater hose, I run into more of the same, just a thin reddish coating, nothing unexpected.

So I went ahead with the procedure anyway. Flushed several times, water on and off, maybe 5 gal total. First flush coming off was a bit foamy (like sea foam). Then put in some radiator cleaner I had lying around. Let that sit for 10 min (cold, with tap water). Then flushed everything out again. Nothing remarkable. Then put everything back together.

Side note: if you remove the supply first, gravity siphons off the water from the heater core through the much longer drain. There is no leftover water to dilute the coolant. Nifty.

Side note 2: If you short circuit the pump relay while refilling to run the pump, the core fills with coolant and flushes out most of the air without having to drive around or encounter an air lock.

Once everything was buttoned up, I started the car to check for leaks. As data points, it was around, say 45 deg F, and the car had been sitting for a total of maybe 3 hours, so cold, but not stone cold.

Nest result: there was some heat in the cabin 30 seconds after turning the engine on! I let it run for a couple more minutes (needle slowly getting off the bottom of the scale, nowhere near normal operating temp) and warm air started coming off. UNREAL. Could not believe that this procedure caused that much of a difference!

I drove out this morning. Within a mile, lukewarm air was coming out. It was warm within 2 miles. This is with the water temp needle not even halfway to the normal operating temp. I now completely get the Jaguar design of High Flow, Low Volume. I had left the water valve disconnected (so, open), and by the time I was near my destination, I had to open the windows for cooling off, it was so hot it became uncomfortable.

So, again, sometimes, cheap and easy maintenance beats throwing expensive parts at a problem. FWIW, if your heater does not behave like I described, put this cheap and easy procedure on your radar. Totally worth it!

 

Well done. Glad to hear that you resolved your issue with minimal expense....