I've been searching thru the forums, but can't seem to come to a conclusion about my heat. My situation seems to be different in that I have some heat on the driver's side, and practically no heat on the passenger side. From everything I've researched, if there is a problem with the Heater core / matrix, then the driver doesn't have heat but the passenger does.

On my 30 minute drive home from work yesterday, with the ambient air temp at 20 degrees F and the engine temp gauge in the middle, I tried the following: set both temps at max temp 89. When driving in town, 30-40 mph, air on driver's side was warm, passenger side cool. When on highway, air was noticeably warmer on both sides, but still not hot. When back in town, air cooled on both sides to back to what it was. I adjusted the temps individually, and the air temp matched between the two when the the driver's setting is at 65, and the passenger's is set at 89.

I've played with the temperature settings, running all the way to cold and back up to hot, changed from vents to defrost to floor, and nothing seems to make a difference. The closest Jag dealer is an hour away. I haven't found a knowledgeable inde.

My guesses are:
- passenger temp sensor bad
- heater core partially clogged
- auxiliary pump weak or failing

Please share any thoughts or ideas you have.
Thanks.

 

It could be a malfunction of the "blend" doors in the dash that directs the air to the vents and mixes warm and cold air to get the desired temp.

It seems to usually be the heater core but I agree that it's confusing that the driver's side is the warm side. ? ?

BTW, I have 111,000 miles on our XJ8 and replaced the blend doors about 3 years ago and the heater core just recently.

Others will chime in to help.

Norm

 

In my experience of reading these forums temp sensors tend not to fail and I have read

that the aux pump is just for idling.

Blend door failures are rare, which leaves..............the heater core.

 

I'm thinking the heater core is the problem as well, but from what I've read, it isn't an easy job to replace the core, and I am looking for a few opinions before I order parts. If the passenger side was warm and the driver was cool, I'd be replacing it immediately, but because my temps are the opposite, I'm not confident that a new core will fix the problem.

 

I'm getting tired of being cold driving - heated seats don't cut it when the temp is in the 20s. Anybody else have ideas? I'm about ready to order the heater core, but I'd hate to spend the money and the time and not have that resolve my problem. Suggestions please!

 

Core replacement is ... well ... challenging but not impossible. Lots of room under the dash, but dang, that passenger seat will get in your way more than you'll like. Under the hood, the challenge is just getting to the hose clamps on the firewall. If it's your first time in either area, be patient and persistent, and respect the air suspension tubes.


As for a clogged core, I had two options - used replacement or reinstall original - and I chose to reinstall the original after a thorough flushing. The core is the perfect sediment trap, so I was not surprised at how much came out. I just kept running various fluids - ammonia, vinegar, soapy water, etc. - and giving it a good shake. It is obvious when tubes are still clogged as water will swish back and forth without immediately running out.


Hope this helps.

 

Thanks for the tips. Did your heat get restored after you cleaned out the core?

 

I must admit that despite Brutal's description of the heater core as a U shape on it's side

with the inlet and outlet crossed over, I still can't visualise how only one side is cool due to a

blockage.

eg Does this mean that in the event of a blockage the in and out temps are similar or will

measuring the inlet and outlet temps reveal a blockage?

Quickcat have you tried flushing the core both ways,it may work and would only cost your time?

 

Yes, the heat is restored.

 

See the included photos of the core. Sorry, they are not the best focus but you can see that the core flow is from upper right to lower right. You will also notice a restrictor in the lower outlet.

Essentially, there is nothing forcing coolant to flow through the left-hand side of the core if the path of least resistance is on the right. Anything that is inclined to get hung up will do so on the far (driver's) side of the core first.

Combine that with the fact the among the highest points in the cooling system is where the tubes pass through the firewall into the interior, it makes the heater core the perfect sediment trap. Double whammy to say the least.

When I removed my core, I satisfied myself that it was clogged by simply running hot water through from the tap in my bathroom sink while the core laid flat on the counter. While the near side quickly warmed up, the far side took much longer. The heat the eventually was felt there may well have been simple conduction rather than from the flow of hot water.

I, too, was a skeptic, but have become a believer. If there is no heat on the driver's side, my money is on the heater core.

Hope this helps.

 

And in all honesty for the extra hour it may take to remove the passenger seat and replace to be able to get better access to the front of the car, would you recommend doing it ?

 

Glad to hear the heat was restored. I'm thinking I might try this route this weekend. Can you give me some additional details as to the various fluids? Straight ammonia? Vinegar? Did you let it soak? Did you try any chemical type products?

 

Too bad there is a restrictor, because I wonder if the core wouldn't both work better and be less subject to clogging if the flow was reversed at the firewall hose connections from lower to upper.

And now wonder the heat is weak on Jaguars, that heater core is puny!

 

T,


Not sure how long it would take, but I'd seriously consider pulling that seat if I do it again. My ribs still hurt two days later from the corner of the seat.

 

I've wondered about flow reversal as well. As it could have been built flowing in either direction, I'll have to trust the engineers that top to bottom is actually preferred.


If, however, you want to give it a go, it seems the easiest place to swap the hoses, and therefore flow direction, is at the front of the wheel well tubes. Just unplug each of them, and plug the top one into the bottom tube. You'll probably need to add some length to the former bottom hose to make it easily plug onto the top tube, but there should be plenty of room for that.


I'd be curious if you proceed.

 

The passenger seat should come out in less than 10 minutes. Just 4 fasteners and a wire harness plug. When I did the headliner job I unbolted both front seats and laid them over sideways out the doors to make it easier. Unless there is something very intricate under the seat I didn't see, I could have easily just pulled it from the car.

FYI 2 of the seat base bolts are star sockets for lack of the proper term.

 

I would have thought that the best arrangement of the connections would have

been in at the bottom and out at the top ,that way you would be sure to

displace all the air in the core.

From what has been said I am sure now that measuring in and out water

temperatures would not reveal a blockage.

I can't see why a restrictor is necessary or what it would achieve-maybe it's

just bad design of the core.

 

Decided to give this a try as all it would cost would be about 8 hours over the course of the weekend. I was able to get the core out following the factory manual instructions, however, I could have eliminated several steps and saved a bunch of time. I read elsewhere on the forum to leave the pipes going thru the firewall and just disconnect at the heater core itself. Although I did take off the engine cowl cover, I probably could have located the 2 hoses without doing that, and clamped them before the firewall, which I did with flat Vice-grip pliers.

The hardest part of the whole project was getting the heating/blower assembly out (and back in). I had to disconnect all the wiring that wrapped around it, and then the unit was somewhat wedged against the center core assembly.

I managed to get the heater core out without losing any fluid in the car, so that was a good feeling. I ran the core under sink tap, flushing hot and then cold water thru it for about 45 minutes. I got a small amount of black particles out of it, but nothing that looked large enough to plug the core. I then filled the core with white vinegar, and let it soak for about an hour. Then more hot and cold flushing. A few more black particles came out. Then I filled it with Prestone Radiator Flush and Cleaner, and let it soak overnight. Then more flushing with hot and cold water. Some more black stuff, but not much. No major gunk. I could look into the top opening, and it looked really clean inside. I couldn't look into the bottom opening, as the restrictor is in the way.

The restrictor was definitely added, as you can see by the attached photo. It is put into the bottom - my guess to slow the outflow of coolant so that there are no air pockets in the core.

I'm feeling pretty confident that the core is not plugged, because when I ran the hot water into it, all the vanes became hot, and when I ran the cold water in, they all became cold. I thought about removing the restrictor, but decide to just open it up a little by drilling a couple 1/8" holes to help reduce the restriction. The restrictor is not metal, but some other type of plastic type material - it drilled really easily. I made sure the were no particles from it left in the core by blowing it out with compressed air, then vacuuming it, then running more water thru.

It took over 2 hours to reassemble everything, as I got stuck trying to get the above mentioned assembly back in, thinking it was going to break as I was forcing it over the stud on the firewall. I finally just went for it, and it jammed back in place. I released the clamps and no leaks. I decided to drive it before re-installing the glove box assembly to confirm no leaks.

Now came the moment of truth. After topping off the overflow tank with coolant, I took the car out for a 20 minute drive. It took awhile, but the warm air started to blow. Unfortunately, I never got hot air, and the passenger side is still noticeably cooler than the driver side.

So the good news is I didn't waste money on a new heater core, only my time. The bad news is the problem isn't fixed. I'm thinking sensor, as I don't think the blend doors would make the passenger side that much cooler than the driver side. I'm open to other ideas though or a way to diagnose if a sensor is bad.

 

QC,


The heat return was not immediate for me either, but after a day or so I was back up to full heat, and the fan settled down. Not sure why, but that is how the system responded.


Anyway, when I had mine out, the shaking up and down seemed to be the most productive way of dislodging sediment. I noticed that as long as I had a slushing sound, I had blocked passages. Was this your observation as well?


I also noticed little difference in using various fluids. Perhaps the nature of my sediment, but soapy water worked about as well as anything else. Which fluid would you say yielded the best results for you?


And am curious as to how you checked individual vanes for temperature change. I had trouble calling the touch test reliable as everything would warm up/cool down quickly as a result of metallic conduction.


I wonder if someone might conjure up a bench test tool for this? I'm thinking a small box fan blowing air through as coolant flows through, and a temp gun to take readings. I have a spare core, so maybe I'll play around and see what happens.


Hope this makes sense.

 

Drove to the NAIAS in Detroit on Monday (approx 3 hr round trip) and still only warm air. Nice display of Jags with an interesting concept vehicle (see below).
Yes, I shook the core numerous times, and that seemed to loosen things up. I'd run water thru for about 1 minute, then shake for a minute, empty and repeat.
The vinegar didn't seem to do anything more than the hot water. After not getting any sediment out, I soaked overnight with the Radiator flush. That got some more stuff loosened up, but it could have been just from soaking overnight.
It was by touch, so not the most scientific. I did try to feel the individual vanes as soon as I'd fill with hot and then cold water. I guess the conduction could have been the reason it felt pretty uniform temp. Looking into the core openings, the inside didn't seem to have any scale or clumps of stuff, so I think it's flowing okay.

With high temps only getting into the lower teens this week, I may have to break down and take it to the dealer. I really wish my issue was the driver side with no heat and the passenger heat, instead of the opposite, as there are so many threads addressing that problem.