Chaps,

Funny problem, the heater has started blowing hot and cold. It'll blow hot for a while, then cold and then back to hot and keep doing this for the entire journey.

Any thoughts?

 

On most vehicles it would likely be the climate control valve. These are solenoids, and can get cranky. However, they normally stick in a position, not wag back and forth. Perhaps the computer that drives it is losing its brain?

 

Duke,

I've had the same issue for 2 winters now. It seems to do this at will. Stopping the car, shutting it down and then restarting seems to solve the problem until the next time it acts up. No rhyme or reason and very intermittent.

Here's a thread that covers the basics of what to check:

https://www.jaguarforums.com/forum/s...ad.php?t=49718

In that thread I mentioned that higher rpms seemed to help my condition but that is not always the case. The last time mine acted up I floored the accelerator and wound the engine to it's shift point twice to no avail.

Until I can do a deep dive into the issue, I just take my other car when it's really cold just in case. It always heats just fine.

Now that I think of it my XJ8 is like my wife...runs hot and cold intermittently. LOL

 

Check your system voltage, sounds like a low voltage computer problem to me. Modern cars start doing strange things in that condition. Restarting may be rebooting (some things keep power, like clock and climate system, but start might cause enough voltage drop to do the boot trick on your computer). I have had all kinds of weird problems on an old Lincoln MK VIII, new battery solved them all.

 

It may also be the electric auxiliary heater pump. That's the symptoms I had when mine was going out.

 

It was intermittent?

Interesting that you mention the pump. I heard a whirring sound up by the cowl on the left side while driving the other day. It made noise for a minute or two then went away. I was getting heat at the time so I didn't connect the two. Instead I thought, "Oh great, something else to fix".

Ken

 

Yes, Intermittent. I have two theories on this:

1. My brushes wore out on my pump's electrical motor, so I figured they occasionally connected, and occasionally did not.

2. Just the heat and standard water pump were able to push water through the heater core occasionally. When the thermostat opened, it would force more pressure and cause the water to circulate.

Both just guesses, but maybe?

 

Thanks guys, will look at the battery but it does sound like it could be the heater pump.

 

My pump motor wore out the brushes, so I replaced them. But, unfortunately, the plastic around them was also badly burned they only lasted a short time before the plastic broke away. Also, the armature was worn badly.

Fortunately, I found a low mileage XJR at a local pick-n-pull and scored a new/used pump for $15! Nice, considering it's over $460 for this thing. Now, my heat is SUPER reliable.

Also, another thing I forgot. If your coolant was mixed with a non-compatible coolant, your heater core might be clogged due to coagulating. That's another thing that went wrong before the pump died. After buying the vehicle, I went through all the fluids, and it appeared the previous owner had mixed coolants because it was thick and kinda like spoiled milk with chunks. I drained all the coolant and ran the motor with a water hose in the reservoir for about a half hour with the radiator drain open. After a while, my heater core unclogged and I got heat. I then replaced all the coolant with new.

 

$460.00!!! for the pump! Yikes!

Hopefully I pulled the one from the 50,000 mile wrecked XJ8 I had. I don't remember if I did, but I have 5 boxes ful of parts and maybe I'll get lucky. Otherwise I'm going to look at sourcing a different pump and making it work.

Maybe something like a Bosch Water to Air Intercooler Pump. They go for about $120.

 

That was my EXACT next step. There's a young kid at my local AutoZone that is very sharp, and he told me he had recently figured out what intercooler pump from a ford interchanged with our JAG heater. He also said it was about $120. When I found the OE used part, I was happy about it and never followed up on the Ford Pump, but in the future, I sure will.

 

Yes the pump I'm referring to is the one Ford used. I'm familiar with it because I had one on my 2003 Harley F150. They also used them on the Lightning and the Cobra Mustangs with the Blower / Intercooler setup. It's a Bosch pump and is available just about anywhere.

I hear it's also compatible with other european vehicles that have intercooled blowers to0.

Here's a pic of my old truck. If there was ever a vehicle I regret selling it was this one.

The interior was black leather, it had 400 hp and because of the wheel base it was an awesome freeway cruiser. Everywhere I went it got looks and compliments. I even raced an unmarked Indiana Highway Patrol car (Black Charger with tinted windows and a Jolly Roger front plate) and got let off because the officer wanted to talk about the truck. Man I miss that truck....

 

Does anyone have an idea what the part number of this alternate pump might be? Or exactly where it is used, so that it can be chased down? Thx.

 

I don't know for sure, but here are a few listings. I doubt the exact flow is super important, but if it's way off, that might be an issue. You will need to do a little wiring, but it's a very easy connetion. Just two wires. And maybe a clamp mounted to the wheel well? I don't know if this would fit the existing bracket, but possibly.

BOSCH WEBSITE: http://www.boschmotorsandcontrols.co...mpen/index.htm

ONLINE SELLERS:
http://cgi.ebay.com/ebaymotors/ws/eB...92004400140321

http://www.ottperformance.com/store/...ump-11p158.htm

http://www.siliconeintakes.com/produ...oducts_id=1001

http://www.needswings.com/Bosch-Inte...schICpump.aspx

http://www.votionspeed.com/servlet/t...rcooler/Detail

And there are MANY more listed on Google... It appears these have similar or exactly the same bar pressures and 317 Gallons per hour. I cannot find the specs on the Jaguar Stock Pump anywhere, but since this same pump comes up everywhere, I'll bet it's it.

 

2000 XK8 with no heat. Heater panel shows no codes, engine temp normal. I want to check the pump to see if it us running. Where is it?

Also does it runs all the time when heater is on?

Thanks all

 

On my '99 XJR (US Model), it's mounted on the driver's side fenderwell by the firewall.

I don't know for sure if it runs all the time or not. Never checked that. part.

Also, check your diverter valve, they also go out.