I have a no heat in the car issue, which I assume is the blend door motors. My question is when car comes up to temp( gauge in middle) heater hoses hot(both sides of heater vave) upper rad hose is cold and coolant reservoir is also cold. No signs of over heating. Temp stays steady. Is this normal???

 

Assuming your car had been running long enough for the engine to be properly up to temperature (sounds as if it was from the gauge position), then you most probably have a have a thermostat stuck closed. Check this ASAP so you do not cook the engine.

I am assuming you have the 6 cylinder version, otherwise there would be 2 top hoses!
Greg

 

If upper rad hose is cold, then the thermostat is stuck shut. I'm not sure how accurate your temp gauge may be. As thermostat reaches opening temp, then top hose will suddenly warm up as hot coolant from engine flows along it.

Get an IR thermometer, check temp at thermostat housing and on top hose just on rad side of thermostat. This should help you understand if stat is not opening.

Good luck

Paul

 

It is new york after all, you sure it is on long enough for the stat to open?
The needle can be in the N with the stat closed, since the stat opens to essentially maintain that temp.

Definitely get an IR thermometer though, those needles can stick.


Btw buy the jaguar genuine part for the stats, too many issues with varying sizes on the v12 bypass system. If its a 6...well id still get the jaguar part the costs is basically the same

 

Thanks for the quick suggestions. Do have an IR thermometer, will put it to good use. will keep all posted

 

Finally got around to changing stat (job, grand kids, holidays). Temp gauge still at center but now rad hose gets warm and flow seems good. Heat in car still issue. Blows hot air at feet for 5-6 mins then cools down. In auto, temp selector all the way to high and water flowing through the heater coil, valve is open. Any suggestions or help will be appreciated.

Thanks

 

When this happens is the air still coming thru the footwell outlets? Or does it change to the upper vents?

Cheers
DD

 

Still comes thru the foot wells

 

Have similar problems. Temp gauge is normal but no heat and no air flow from center vent. Car (92 xjs) is in shop, will post when the bill is presented assuming I am still upright. This car is worse than the boat I sold because it was costing more in maintenance and repairs than almost what I paid for it. I guess I'm a slow learner.

 

I think that heat will never come through the center vents by design, only cold when the ac is on and it is trying to cool. Warm will only go to feet and rear and sides and demist. The older vacuum water valves can and do stick either open or shut, depending on where they were last. There is a generic plastic replacement that is easily available but a bit tough to change.

 

Vacuum water valve works fine. Is normally in open position when no vacuum applied, as is the case when heater is on. I'm suspecting upper and or lower blend door positions might be the culprits. Odd that it works for several minutes delivering ample heat. Will fool with cabin temp sensor. Any one know the normal ohms across the terminals....

 

Ok, good.

If the air gets cold *and* starts coming from the upper vents it would suggest that the system 'thinks' cold air is being asked for and is dutifully obeying orders.

Or it 'thinks' the cabin is too hot and is trying to cool it down.

Since the air still comes from the footwells we can probably assume the brains of the system, so to speak, still recognize your request for heat.

Cheers
DD

 

Sounds plausible



As you wish, but if there was a problem with the cabin temp sensor.....for example sending a 'cabin is too hot' signal....I'd expect the system to respond by going into cooling mode. This means sending air to the upper vents...which is not happening.

I don't know the resistance specs, sorry.

Cheers
DD

 

Any chance of an air pocket in the heater core? On a V12....where the cooling system is very prone to air pockets....an air pocket can travel into the heater core and result in cold air. Been there, done that.

I know (or assume, actaully) you have a 6 cylinder which is much less likely to have air pocket problems but, still, I thought I'd toss the idea out there!

Cheers
DD

 

Thanks for the thought about an air pocket, had that problem with a BMW several years ago, but I'm pretty sure the core is flooded. I can feel the heater hose temp rise as I increase the RPM. Manually closing the valve cools the same hose...and yes it is a 4.0

 

My heater core is clogged shut, so I have no heat, but after a restart it blows warm for a minute or so.

I think when I shut the car down and come back after 10 minutes or so, the heat has soaked in the heater core a bit and so it blows warm for a minute or so, until the radiator starts cooling and all the water gets pumped around again. Idk though, not a big enough deal to look into for me

 

Heater core flows freely, doesn't seem to be clogged

 

Time to go back to your earlier idea about a problem with the flaps where incoming air is directed away from the heater core.

First you'd have to verify that it is actually happening and then of course figure out why. Do you have the repair manuals for your model?

Cheers
DD

 

Yes I have a repair cd but heating and ac sections are short on trouble shooting. I have also downloaded Delanair service manual from site, better but still a bit vague......I was hoping someone out there had similar problem and found the fix. A time saver for me, but alas doesn't seem to be in the cards..Will start with checking for proper connections, GROUNDS,suspect wires and operation of both blend doors and general integrity of system...again any ideas are very helpful.

 

You're on the right track. I've fixed a couple wonky Delanair MkIII systems just by cleaning grounds and connections. And, if you eventually DO to get into electrical tests you'll need to begin with known-good connections or the test results can't be trusted.

Cheers
DD