XJ XJ8 / XJR ( X308 ) 1997 - 2003

'00 Jaguar XJ8 Vandan Plas - No Heat in Car

Old 10-12-2018, 07:12 AM
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Default '00 Jaguar XJ8 Vandan Plas - No Heat in Car

Hello, asking for this groups advice once again. The 2000 Jaguar Vanden Plas I inherited and sat for 6-7 years prior to me working on it now does not have heat in the passenger cabin. I have been working on this for months and through I got to the point it was all back together and running well. Today, it got cold (finally in SC) and when I went to drive it to work I realized the heat will not come on and will only blow cold air (no AC on).

I did check to see if the coolant level was correct and it is and also ran the car with my OBD scanner on it and the temp of the coolant is correct. I have no check engine light.

So any suggestions on where to go and where to start looking in the process on why the car does not have heat would be greatly appreciated.

Thank you all in advance.
Old 10-12-2018, 09:31 AM
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A common culprit is the auxiliary pump, located on the driver's side fender well near the brake booster compartment. Plenty of info in the forms on it. It's not too hard to change out for a replacement, or to pull out to replace the brushes which tend to wear out over time. If you do find a replacement pump, it can be swapped out in 10-15 minutes without too much fanfare.
Old 10-12-2018, 09:53 AM
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You might also want to check the ambient air temperature sensor. Press the EXT temp button on the AC panel and see if the reading is close to what the actual outside temperature is. Mine was reading 138 degrees when it was 45 degrees outside and wouldn't let the heater work. You can also test the pump by pushing the red temp button until the display reading is HI. That takes the sensor out of the loop and gives you manual heat. If you get heat then it is most likely the sensor.
Old 10-14-2018, 05:31 PM
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Default Still no heat

Thanks for the advice so far. I have determined that I still have no heat after series of troubleshooting steps.

Step 1 I checked the sensors in the car and the EXT when pushed reads the proper outside temp and I did set it to High with no luck

Step 2. I removed the heat auxiliary pump disassembled and rebuilt, and confirmed that it was running by putting a charge to it before reinstalling and still no heat.

So heat are my questions

1 Can it be a failed thermostat especially since the car set so long. Will that cause no heat in the cabin?

2 can the heater core be clogged. I can back flush it but where do the tubes come through the firewall to disconnect so I can back flush it

any suggestions would be great.

Thanks again.
Old 10-14-2018, 06:57 PM
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Default Problem Solved

well after reading in another forum site they said to swap the heat relay with the horn relay. When I went to do this I found out that the heat relay was missing all together. Why no idea since I inherited the car. So got a new relay and no have heat.

thank you for all for your help.
Old 10-15-2018, 05:14 PM
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I also had the no heat problem. I replaced the aux water pump by the brake booster, that didn't fix the problem. But, I did find the other valve located right next to it and replaced it. Then, I got heat. What a Pain it is but nice to have heat
Old 10-17-2018, 01:42 AM
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I've had this issue recently albeit on a car that is regularly used, I did a complete overhaul of the system in the end just to be on the safe side. In your case with the car having sat for 7 years I would do this anyway as coolant becomes gunge if it's left to fester. At the very least I'd be looking to flush the whole system including matrix, replacing the thermostat which is likely gummed up, replacing the expansion cap and checking the heater valve others have mentioned. The best way to approach this is by dropping what coolant is in the system with the tap at the bottom of the radiator. Removing the expansion cap will allow this to flow out quicker and easier, then check your hoses. Once you've got as much coolant out as you can, begin disconnecting hoses, but be careful of the plastic ones running from the expansion tank to the radiator, they are fragile. Remove the aux pump and the valve and clean, but make a careful note of where they're connected.

Once you've replaced it all and refilled with the correct coolant type, fill up the system and allow the car to idle with the heat set to HI. You may have to rev up to 4,000rpm to get it to burp properly, and for heat to come through. You must keep an eye on the level and once it's cooled down check and top up as required.

One other thing to check is the interior temp sensor which lives behind the grilles on the boot/trunk opening switch. It's connected to another unit which has a small fan in, it may be clogged. Consider removing and cleaning this too.
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