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Did something stupid...now I have NO HEAT!!


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I have read the posts/threads regarding no heat, but I have somewhat of a unique/dumb situation. I bought a 2001 XJ8 with 78K miles . When I bought the car, everything worked including the heat. But it did have a small coolant leak, just couldn't determine where the leak was. After driving the car for awhile leak got worse and i put a bottle Of Bar's Stop Leak down the coolant reservoir. Bad move!! At first everything was fine. Then the heat went out. I had the car looked at by a mechanic Thermostat housing was bad. Had it fixed. Still no heat!! Figured I had clogged something up. Had the system flushed, all hoses removed and checked for blockages. And the Heater core was flushed with water until it was clear in both directions. Also had the AUX heater pump and Heater Control Valve removed and taken apart to inspect for blockages All Clear!! Still NO HEAT! I have disconnected the AUX Heater Pump, so that I can feel the difference when its connected and running and when it's not. It's definitely running. I can't tell how warm the hoses are by the heater core/heater control valve because it's so much engine heat in that area. But i know the hose from the AUX heat pump is Luke warm at best. All other hoses are hot. Not sure how to test Heater Control Valve, but from what I read they don't go bad too often.

What am I missing? Is is possible I could have messed the pump up with the Bar's Leak? Only thing we haven't done is remove the Heater Core from the car. But like I said, mechanic "said" he flushed it. I get no heat when i idle the car at 3000 rpms or when I drive down the highway. I welcome any and ALL suggestions. Please chime in. I hate to just start throwing parts at it.

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Hi Donald, and Welcome to the club.


It appears that you have done all the things I would suggest.  I am not an engineer, just an old and experienced person who enjoys nice cars.


I would be inclined to start from a fairly simple basis by going through the Air conditioning settings which are quite similar on the XJ to my S type.  I know it sounds a bit elementary, but sometimes missing the obvious is very easy.


Let us know how you get on.





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it could well be a air lock drain water start engine with heater on hot and blower on max

and fill slowly hope this will fix


Thanks Trevor and Old Peter!! 

Trevor, when you say Air Lock...is that the same as bleeding the system? I saw the mechanic open/loosen the  bolt on the thermostat housing while filling up the coolant reservoir. Said he was bleeding the system. is that the same thing? With an Air Lock, would I be getting NO heat at all or very little heat? Car Temp stays perfectly in the middle. I did the the Diagnostic mode on the Climate Control, NO codes stored. Heat did work when I first got the car. Didn't go bad til I put the Bar's Leak in the system.


Thanks Again for you help in figuring this out with me!

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I can see what he is saying.    If it were me id drain all the water from the engine again.  Loosen and remove one end of the lowest hose, and dont forget to remove the radiator cap :) Dont forget to open the heater controls. Tighten everything back up again. Keep the heater controls open on full heat.  Slowly fill the car back up with water. Occasionally squeezing all the hoses to get rid of the air.  When its full leave the cap off and run the engine.  Squeeze all the hoses again to get rid of the air.  Watch your fingers those moving parts can hurt.  Top up.  Put the cap back on.  As it pressurises loosen the bleed screw to get rid of and air remaining.  You may find the water level may suddenly drop a little  as the car gets hotter.  That just means the thermostat has opened and allowed full circulation.  You may have to top up and bleed a few times before you get rid of all the air pockets.


  If its possible try to get the front of the car higher than the back.  Bubbles always like to rise.  Good luck.  You will let us know how you got on wont you??

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Good idea, Frank.  Air Pockets  ---  I never thought of that, especially as Donald's car had been in the hands of a mechanic.  We all assume, not always correctly, that if an "expert" has had the car in his hands then he has done everything correctly.


My son found his mini leaking  oil  after a reconditioned engine was fitted. I found that the rocker box gasket was twisted.


I had a old beetle that a wheel came loose and nearly off after an MOT.





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hi all

most air locks will be in the heater unit. frank you got it spot on

I don't think its much more then air remember the old cars peter

air locks were common after you changed the anti-freeze

I still get this at work with the lorries some times it can take

two or three times to get the air out.[YES PETER EVEN AFTER WE HAVE SEVICED]



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