XJ XJ8 / XJR ( X308 ) 1997 - 2003

heater not working

 
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Old 11-30-2009, 08:31 AM
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Default heater not working

My car will heat up just fine but the heater doesn't work sometimes and other times it will I checked the fluids and they are good and its cold now so any ideas??
 
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Old 12-04-2009, 07:55 PM
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Two things. There is an aux. pump on the drivers side of the car mounted low just in front of your strut mount. If you turn your car on,you should be able to feel it vibrating from the pump turning. You can check the connection,also put 12V on it to see if it works. Next is the bypass valve. You have to remove the black cover that runs across the back side of the engine firewall. Under the coolant housing is the bypass valve. It's electric as well. The bypass valve is not cheap. You can by a couple of metal connectors & clamps and remove the valve. After driving for 20 minutes you should have heat. You would have to replace again in the spring in order to get the A/C working again.
 
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Old 12-05-2009, 02:15 PM
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Perhaps you need your A/C system recharged? My Dad's MG ZT had a similar problem and recharging the system fixed this. I never have my AC off, I just leave it on Auto and set the temp, after having my XJ's recharged also the system worked better.
 
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Old 12-06-2009, 07:32 PM
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i remember a few weeks ago i did hear a vibrating sound coming from my feet when i started the car then it went away after a min or so.. but i guess since then my heater has had a mind of its own...aux pump then?? and would i have to buy a new pump or is there some replacement kit?
 
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Old 12-12-2009, 10:42 AM
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It could be the pump but (as in my case) it is the water bypass valve. There is a valve in front of the little pump that diverts hot coolant into the heater core. In the summer, with the a/c running, hot coolant will not flow into the heater core - simply because the A/C cannot over come it. In the winter (heat demand) the valve is supposed to allow hot coolant into the heater core.

In my case, the A/C worked REALLY well during the summer but in the winter I got no heat at all. I checked my aux pump and it was working fine. I then took the valve out and bypassed the coolant lines directly into the heater core. Now I have excellent heat (a bit too much) but the A/C basically no longer works as it cannot overcome the heater core.

So I will be fixing/replacing the valve soon.

Check the valve and the aux pump. From what I've read it is usually the aux pump. I would also recommend that you label/mark the hoses/connections before doing anything. It is quite a maze of lines in that area.
 
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Old 10-22-2012, 10:03 AM
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I've had my Xj8 for about 6 years now, and the heather has never worked properly. You got a trickle of heat from the front vents, but almost nothing in the footwell. About a fortnight ago, the heat stopped all together, and with winter coming up, I had to do something! I had already changed both the pump and the valve a couple of years ago, with no result. This time, I removed and checked both pump and valve, and then did a backflush and straight flush several times on the heather matrix using a garden hose connected to my outside tap. I couldn't see if anything came out of the matrix, as the water tap is 100ft or so away, but it seems to do the trick! Heat all you want now, abd delivered very quick indeed!! :-)
 
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Old 10-14-2013, 03:39 AM
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Update on the heater from last year. The heat was reasonably ok for the winter, and of course the heater wasn't used in the summer. Yesterday, in chilly weather, the heat didn't come at all.
I took the pump and valve off (for the third time), and tried to blow through the matrix, but it was completley blocked.
I connected the garden hose to the matrix pipe, as last year, but this time I had my partner turn the tap on while I looked to see what came out of the matrix.
Then woosh! white gunge came out all over the engine, followed by a nice stream of clean water.
The heater now is working better than ever, like new I think.
My theory is that someone put engine oil in the coolant filler, it found its way into the matrix, settled in the still water during the summer months when the heater is switched off, and emulsified. But I may be wrong.
Anyway, I am going to turn the heater on regularly, so that the aux pump flushes the matrix.
 
Attached Thumbnails heater not working-misc-016.jpg   heater not working-image.jpg  

Last edited by Billwood; 10-14-2013 at 04:17 AM. Reason: Copy of pics
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Old 10-14-2013, 09:25 AM
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For anyone who's interested, I posted a detailed accounting of rebuilding the auxiliary heat pump (most die from the brushes eventually getting consumed) on the JCNA forums. The thread is entitled:

Dead Auxiliary Heater Pump MNC6710AC? Read on. . .

I hope this proves helpful.
 
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Old 01-11-2019, 05:36 PM
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Default Quick cheap fix for the winter

I had no heat as well and it was the pump, rather than getting the costly pump replaced i butchered up the already existing coolent hoses and rerouted everything to completely bypass the valve and pump.

The picture attached shows my method of ensuring flow through the heater core. Hopefully the engine is alright with it xD

 
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Old 01-11-2019, 05:44 PM
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Originally Posted by VandenPlazz View Post
I had no heat as well and it was the pump, rather than getting the costly pump replaced i butchered up the already existing coolent hoses and rerouted everything to completely bypass the valve and pump.

The picture attached shows my method of ensuring flow through the heater core. Hopefully the engine is alright with it xD
Interesting, keep us posted on the outcome.
 
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Old 01-11-2019, 06:00 PM
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Outcome is fantastic heat and the engine is staying at proper operating temp! I can feel my fingers again!!!

Who'd a knew a parking lot mechanic could figure out a better way of getting coolent to the heater core than with an external electric pump? Now what to do once summer comes around....
 
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