Great AC, only some heat
 

Hello all,
My '94 Xj6 has great AC with enthusiastic blower performance, but when asking for heat I get only a little heat from the floor vents... I am going to replace the thermostat as the engine takes some time to warm up. Could the thermostat be my problem? (the heat isn't any better when it finally does warm up...)
Thanks!

Hi hayrancher,

Welcome to the Jaguar Forums! We love Aspen and have visited several times (the Maroon Bells are spectacular).

A coolant thermostat that has failed open can definitely reduce heater performance since the coolant never has a chance to reach full engine operating temperature.

The heater core could be clogged with corrosion, or with a leak-stop product like Barrs Leaks if it's ever been used on your car. If I recall correctly, one quick test for core blockage is to carefully feel the two hoses at the firewall that feed the heater core while the engine is running at normal temperature and the heater controls are set to high. If one hose is hot but the other lukewarm, the core may be blocked. If neither hose is hot, suspect the heater control valve:

On your '94 the heater water control valve is mounted to the left side of the cylinder head under the intake manifold near the windshield wiper motor. If it is stuck closed or partially closed, you won't get sufficient coolant flow through the heater core. See the photos at the links below:

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

You may also have a problem with one or both blend flap motors failing to position the flaps correctly. The photo albums at the links below will give you an idea of how they work:

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

Cheers,

Don

We live on Maroon Creek, just down the road from the Bells... very pretty but its gonna get too wintery for my jag here pretty quick!
Thanks so much for the response! I will do some heater testing...
Another observation; although it has only 77K miles, and uses less than 1qt of 10w-30 in 1500 miles, it does puff some smoke on start up. (like a 911 might!) Anything to do here?
Thanks again!

They all do that.

Valve seals go on these motors, a bit embarrassing but no real problem - Don will explain better!!

Larry

Gee, thanks Larry! You know very well that you can explain it just as well if not better.

OK, hayrancher, here's the simple answer: The valve stem seals are made of rubber. Given that they live in a very harsh environment on top of the engine, they harden over time and lose their ability to seal. The seals are shown as Part 10 in the diagram below:

https://cimg7.ibsrv.net/gimg/www.jag...01721cc4e5.jpg



Unlike the earlier XK straight-six engine, the AJ6 engine is tilted at a 22-degree angle to allow for a lower hood (particularly important in the XJ-S in which it was also used).

When the engine is shut down, the oil that continuously splashes the camshafts to keep them lubricated stops splashing and pools on top of the cylinder head. And because of the tilt of the engine, the pool of oil is deepest along the exhaust valve side of the head.

Because the rubber valve stem seals have hardened, they allow the pooled oil to leak down the valve stems and onto the backs of the valves, where it then drips into the combustion chambers. The longer the engine sits, the more oil that drips into the cylinders.

When you start the car after it has been sitting, the oil in the combustion chambers is ignited, creating the puff of smoke from the exhaust until all the oil is consumed.

There's really no point in doing anything until you need to replace the head gasket, at which time replacing the valve stem seals is simple. But what most of us have discovered is that the seals harden in just a few years anyway, and the puff of smoke returns. So just embrace the smoke. It's part of the XJ40 charm. :)

For the historians among us, I recall that the early AJ6 engines only had the rubber seals installed on 12 of the 24 valves, and if I'm not mistaken, it was the intake valves that were sealed and the exhaust valves that were left unsealed (as shown in the parts diagram above). In the mid-'90s, early second and third owners of XJ40s began having to replace the head gaskets at 90-100k miles and the routine was to order two sets of 12 seals and seal all the valves. At some point Jaguar began installing seals on all 24 valves and retroactively specified the same for earlier engines when they were serviced. I can't remember when this happened (1990 maybe?), but I know that our '88 came with only 12 seals and our '93 came with 24.

If I gotten any of this completely wrong, I'll use the excuse that I'm really tired. I just re-read my sentence about this being the simple answer. Oh well. As Mark Twain once said, "I would have written a shorter letter but I was pressed for time."

Cheers,

Don

Thanks Don,
I had the same issue with a 1967 land Rover series IIa. Ended up adding valve guide seals to that engine which didn't really help...but then a car that old really should smoke a bit!
I might try parking the other way in my drive and see if I can keep that side of the engine up, but It's a great looking and running car; never mind a little smoke!

I have to say I wish I had thought to replace that valve when I had my manifold off fixing a coolant leak.

As far as the valve seals go I tell myself it's just excessive HP being burned off.

So, I took out the lower blend motor and hooked the battery back up. With the CCU on the motor just turned clockwise...view from the front. Round and round. this can't be right!
And the upper blend motor seems to be very hard to get to. Airbag and other stuff in the way. Any ideas about the lower motor going around in one direction? Manual setting and varying the temp made no difference.

Hi hayrancher,

The reason the motor just spins in one direction when it's disconnected is because the position sensor that tells the CC ECU when to stop turning the motor in one direction is mounted on the other side of the CCU. When you pull the motor, the blend flap is no longer turning so the position sensor is not turning, and the CC ECU is confused. It keeps expecting the position sensor's signal to change, but it doesn't. The fact that your motor is running at all is a good sign.

I don't know if you checked out my photo albums on the blend flaps but there's quite a bit of info there. You probably will have to remove the airbag to access the upper motor (our '93 has a glovebox where your car has the airbag). Before you go to that trouble, you might see if you can get the handle of a screwdriver up in there so you can tap on the motor case to free up the motor in case it has siezed in one position. Several owners have been able to get the motor turning again just by giving it some good raps on the case.

Cheers,

Don

I replaced the thermostat and now have normal operating temps. Followed your instructions and was able to tap the upper blend motor with a cute little hammer whilst selecting warm and then cool air and was able to free it up! I now have great heat and AC!
Drove from Aspen to LaJolla to take my 16 year old daughter to the beach and the Jag ran like a champ...85mph and 25 mpg. Smooth and quiet. Thank you so much for the help!