Hello all! Well it seem that I have my yearly heating issue once winter gets here (at least its something different each time to keep it interesting!). It seems that I am only getting somewhat warm air with the heat cranked. Now, the usual suspects: DCCV - Just replaced last spring, all vents same temp and AC still ice cold; Aux coolent pump - again, replaced last spring due to no heat last winter. So, I am 99.9% sure the DCCV is fine, same with the Aux coolent pump. Also, when the aux pump wasn't working, I got NO heat at all unless I as driving around at about 4000rpm, and even then just a little. This time revs make no difference. I have also replaced the relay for the aux pump, no difference. Also, all the in cabin temp sensors are new and by setting it to HI (bypassing the sensors) still same result. However, I noticed that if I set it to Recirc, instant burn you face off hot air, then once its off, back to just warm air. Now, I do have a spare RCCM that I may just swap in and see if it makes a difference, but I have never heard of one of these going bad. After doing some reading, I am wondering if a blend door is stuck or not working properly. If something is stuck open, it might be letting outside cold air sneak in with the warm, but with recirc on, no more cold outside air so it works as it should. The blower and fans all seem to be working fine as well. So, other than maybe switching between all the vent settings to give the blend doors a workout, any ideas, cause I'm running out of them!

I should add that I have yet to try a hard rest yet, maybe something has just 'fogot' its position! Simple things first!

 

Are you still running your factory thermostat? It may have failed....

 

I am still on my original one. I had meant to change it when I did my blower removal, but got the wrong one so I never changed it. It did look like new when I had it apart, but I hadn't considered it since I haven't noticed any problems with the engine heat. Wouldn't there be some other signs (which I just can't remember right now!) if my t-stat was on the way out or already gone?

 

I have the same issue... and I am in Regina, Saskatchewan where the winter temperatures gets to a very cold -40F. Needless to say I hope to get it fixed soon before the temps here really dip down.

I have replaced my heater core(a monumental chore BTW), T-stat also replaced, and have even replaced a cracked overflow tank.... still not fixed. I do get some heat when idling now but the blowing air turns cold again when driving. I am now looking at having the pump replaced.

The closest Jag dealer is 2 hours drive so I have limited access to a knowledge base except on this forum. Any ideas would be appreciated?

 

https://www.jaguarforums.com/forum/x...er-core-85672/
I CAN AT THIS POINT PRETTY MUCH TELL YOU THIS IS YOUR PROBLEM. YOUR ONLY HOPE IF SO IT TO DISCONNECT THE HOSES TO THE CORE OFF THE METAL PIPES THAT ARE BY THE DCCV AND BLOW COMPRESSED AIR THROUGH THE CORE AND HOPE IT DESLUDGES ENOUGH TO RESTORE FLOW. OTHERWISE I WOULD REPLACE THE CORE

 

Dang Brutal, you reverted back to capitalized text? Anyhow, ditto to BRUTAL. Compressed air...you hosers.

 

Well, I may have to blow out the heater core. However, as of yesterday morning, as mysteriously as it stopped working, it started again! Got in the car, about -15C, and guess what, good heat. No idea why, and it's been working fine since. Now, I had been playing with all the climate control settings for a while (as in pressing every vent setting, recirc, Hi, LO, etc over and over again in random combination) and maybe there was a stuck flap somewhere. Or possibly there was some crude in the heater core that decided to dislodge itself. Either way, hopefully it will keep working. If not, I'll have to take Brutals advice and blow out the heater core and see if that does it! The real test will be when it gets really cold here and see if it still has good heat. One things for sure, these cars sure keep you busy!

 

Bfg, no im always in caps at work, unless i hit shift and make a lower case letter, or in that post i linked that thread which before it posts it got lower case in the link text. Otherwise my all caps posts come in all lower case as this one will which im in caps right now but when posted will be lower aint it great

 

LOL! Brutal, I was going to use Caps but worried about violating copyright laws concerning your brand. Take down Romney/Ryan and replace with Revolution? Winterjag, sounds like an air lock in the core to me?

 

Now that you mention it, an air lock does sound like a probable cause. I have drained and refilled that cooling system a few times over the summer and fall fixing stuff. And maybe cause it was hot and I never needed the heat, some air just got trapped in there and never worked its way out. Hopefully whatever it was has fixed itself! Now onto sorting out the reverse sensor problem!