The Mk2 Jag heater in original form is the subject of much (partially justified in my opinion) derision. Many British cars from the same era suffered similar afflictions. True it didn’t produce much de-misting or rapid heating effect, but it did get the job done — eventually. There’s no doubt that the performance is poor by modern standards, so anything that can be done to improve things is worthwhile.
Anyway, I’ve had a heater upgrade kit sitting in my workshop for several years now, which I purchased from the Daimler and Jaguar Spare Parts Club. Clayton Classics produce this kit in the UK; I assume they still provide it, although it’s not mentioned specifically on their website. Lin Rose used the same heater upgrade, check out his site for additional detail including an article from the January 2010 edition of Jaguar World on this upgrade. The Kriss Motors Mk2 Restoration details a more sophisticated approach.
For me, heater performance isn’t a top priority, so I’m happy with the Clayton Classics upgrade.
The upgrades to the heater are outlined on Clayton Classics website:
- A new copper heater core
- A more powerful fan motor coupled with a larger diameter fan wheel
- The inner air flap is sealed permanently shut
In the Jaguar World article they state the reason for sealing the inner flap shut is that, over time, the seals on the flap deteriorate and the warm air is diluted by cold leaking past the seals. I also wonder if the system of cables and rods operating the heater valve and vent cause problems as well. I’m certainly no expert, but I’ll see if it’s possible to get this all working properly￼.
Of course, another option is to have the original heater core reconditioned … hmm sounds too simple.
Here are some images of the heater before I removed it from the engine bay.
Whatever the final approach, the first step is to assess the current condition of the heater unit and pull it apart — always the quickest part of anything to do with classic cars!
I started the disassembly process by removing all the linkages to the heater valve and control flaps.
Water valve — The water valve is attached to the heater body with two machine screws, the valve was stuck in place (hardly surprising after nearly 60 years!) but it came out as I rotated it back and forth. Later I realised that the inlet pipe to the heater core had come out with the valve.
Fan motor assembly — First I removed the nut holding the squirrel cage fan onto the fan motor, I needed to lock the cage with a screwdriver to get the nut moving. The motor is held in place by three set screws accessible from the inside of the heater body. Three nuts attach the motor mounting points to these screws along with two rubber isolating washers on each screw. There is a separate bracket to which a wire wound resistor, for the low fan speed setting, is mounted.
Heater core removal — Eleven self-tapping screws hold the lid onto the heater case, these unscrewed easily. I then carefully prised the lid from the case to expose the heater core. I wasn’t quite sure what to expect when I first peeked inside, but the interior was quite clean, with the remains of only a few dead insects.
The heater core slots into position and was easy to remove, you can see in the images below where the inlet pipe pulled out of the old core.
I then gave the now stripped down case a good blow out with compressed air to make things a bit cleaner for the required modifications to the case.
Heater case modifications
The kit came with a printed set of instructions, and here is a colour PDF version which I downloaded from Lin Rose’s excellent site. First, I tackled the case modifications allowing the larger fan and more powerful motor to be fitted.
Enlarge the air intake — The intake is enlarged to 120mm diameter to accommodate the larger fan. I masked the air intake with tape and marked out the cut line needed for the increase in diameter. I used a jigsaw to cut along this line.
Up-rated fan motor — The new motor comes with a plastic mounting bracket and a steel mounting plate, three 12.7mm holes are drilled through the heater body for the new mounting plate. I spent a bit of time lining things up so that the holes weren’t too close to the very edge of the case; this meant that the motor shaft wasn’t precisely centred in its hole, but I made sure that the fan fitted ok without fouling the side of the case before drilling the holes. I ran into one issue which was that the motor mount supplied in my kit didn’t have the edge cut-off, and therefore wouldn’t fit as both the mounting plate and the motor mount need to sit right up beside the edge of the heater box.
I used the mounting plate as a template to draw a cut line on the base of the motor mount. I assume my kit had the wrong part in it. I asked Clayton Classics about this; but apart from confirming that cutting the edge off the motor mount was the correct course of action didn’t clarify if this was the wrong part, and I didn’t follow up.
10mm access hole for fan grub screw — This hole is 20mm below the fan mounting face on the case, I used a stepped drill, a new toy which made a nice clean cut.
Motor mount — The motor mount and mounting plate mount onto the heater body with three number 6 x 3/8″ self-tapping screws provided in the kit. The motor is bolted directly to the mount. When it came to fitting the fan, I found it simpler to position it in the enclosure first and then loosely fit the motor shaft to the fan before tightening down the mounting screws.
Resistor — Clayton Classics provide a new 2.2 ohm resistor for the low-speed setting which can be mounted anywhere on the case by the motor. I left this step to last.
I guess you could say that a resistor is a pretty crude way of providing the low fan speed option, but it has the benefit of being simple and effective.
Bench test — Once completed, I gave the unit a quick bench test. At full speed, the motor and fan seem to provide plenty of air.
Preparation for painting — I stripped the paint and rust from the case in my blasting cabinet, well the majority of it anyway. I haven’t quite got the cabinet working as I would like yet, so this wasn’t entirely successful. To keep things moving, I took the case out to The Surgery for final preparation and painting.
Heater Con’t – January 2021
After a bit of a hiatus working on other aspects of the Jag, I recommenced work on the heater.
As mentioned above, The Surgery completed the final preparation of the case for painting. I was pleased with the results and the quality of the matt black epoxy finish.
Once I had the painted heater box back home, I started the final assembly of the heater components, beginning with the motor and mounting hardware. I used three 4mm nuts, bolts and washers rather than the #6 sheet metal screws supplied in the kit. I had to drill the holes out a bit, and it took some fiddling around to fit, but I felt the motor was quite heavy for the sheet metal screws, although they are simpler to install. I applied some Loctite to the threads as the downside of this modification is the inability to tighten things up if they loosen off.
Clayton’s instructions state that self-adhesive foam is applied to the outer flap and around the heater core, and the inner flap is sealed shut. I decided to stick with the original design, with both flaps operational. My reasoning is that the intended use of the Jag is in (hopefully) warmer weather and therefore I want the maximum flow of fresh air into the cabin.
I purchased some self-adhesive 3mm Neoprene foam which I hope will provide a good seal over time. Getting the foam into position on both sides of the inner flap was pretty tricky, I practised with some paper templates to get the hang of things, before applying the self-adhesive foam. Once that was done placing the foam on the inner side of the outer flap was very straightforward.
The next step was to fit the heater matrix; as per the instructions from Clayton’s, I applied the foam supplied in the kit to the outside of the matrix. As there wasn’t enough to go completely around the matrix, I used some of the black Neoprene foam I purchased for the top. The foam cushions the matrix against the heater casing and lid. I tried to fit the matrix with 1.5mm foam wrapped around it, but the fit was too tight, so I used the foam supplied in the kit which had more “give”.
I then fitted the lid onto the heater case with 11 x 6G sheet metal screws.
The next step was to fit a new 0 ring and water valve onto its bracket on the heater lid.
I haven’t as yet ordered the correct flap return springs, but in the meantime I found some that will do the job at my local Bunnings Warehouse.
Ah, the old heater box. I remember it well.
Great article – I just acquired a 1961 Mk2 (3.8) and have started the tear down. Water systems first. Surprisingly the heater core and valve were in great shape. The motor even worked, but was slow and squawked. I wanted to take it off and lubricate it. I am having really problems getting the squirrel cage off the shaft of the motor. Nut no problem, but stuck fast. Any hints?
Thanks for reading my blog. I’ve seen an old Jaguar World article where they give the shaft a squirt with penetrating oil and then use a couple of flat bladed screwdrivers to lever the fan off. That may not be the best if you intend to reuse the fan though. I’d be tempted to heat it first and then try a bit of oil. Good luck!
Ended up having to grind the end off the shaft and clamp nut to get it out. The fan motor is shot anyway. The cage is heavy and quite corroded, so looking for a replacement. Clayton don’t seem to respond.
Fundamental question : which way does the air flow? I assume from the scuttle air intake through the squirrel cage to the heater matrix (or other depending on flap settings etc..). Really just trying to define the airflow. CW or ACW doesn’t really matter so long as the squirrel cage sends the air from the round hole in the back to the heater, right?
Anyone got a favourite used version from something else?
Hi, That doesn’t sound like fun. Yes, the air enters from the scuttle intake. According to the documentation from Clayton’s the fan rotates ACW when looking at it. As for the fan motor and fan wheel, Kriss Motors (see link on sidebar of my site) may be able to help as they upgraded these components on their restoration.
This is a really good article but my question is related to the last comment.
The fresh air intake, I assume, comes from the vent under the windscreen – if the vent is open. If it’s closed, does the air get pulled from within the car.
My car has A/C so none of the current air paths are part of the system, however the scuttle vent still works and I’m curious where that air feed comes out in the car because I’d like to route it to the A/C fan.
I’ve looked everywhere for pictures, sketches and drawings and have found nothing. Are you able to give me any clues?
Hi Peter, Thanks for reading. Yes, the fresh air comes from the scuttle vent. To get recirculated air the manual states that you “close the scuttle ventilator” and set the controls as required. The air from the scuttle vent comes through the heater and back into the car. It enters the heater box through the round opening in the engine bay. The recirculated air must enter the heater the same way. I’m not sure this is any help as I don’t know anything about the models fitted with A/C. I’m going out to check a few things on the body later in the week and can have a closer look if you think that’s useful?
The picture is the one that saves 1000 words ! That’s the bit that I’ve been missing – my car’s A/C is an after-market fit done by me but actually installed by others. As far as I’m aware there was no factory AC for that car. Now that I can see how the air gets into the heater, I can work out how to provide a fresh air feed to the fan, which is now located in the passenger footwell. I bought the AC system from RetroAir in the US, but there is some significant modification required to bring it up to an acceptable standard, including modifications to the pulleys, engine fan arrangement, relays and so on. The AC venting in the car leaves a bit to be desired, and I’m up to that point in this work now. If you are interested, I can take some photos and send them through.
Hi Peter, Yes I’d be keen to see some pictures, I’ll send you my email address. Cheers, Phil
Hi i have a problem with my heater box , is there some kind of seal where it fits against the bulkhead as i have a serious water leak into the passenger footwell .If i pour water over the top of the heater it floods the footwell i assume there must be a gasket or something inbetween any help appreciated thx nick
Hi Nick, Thanks for reading. Yes, there are three seals between the heater body and the bulkhead. One circular (seal) which seals the air intake to the fan, another at the bottom of the heater where the hot/cold air enters the interior from the heater (right at the bottom of the heater, where the outer flap is located), and another (at the rear) where the demister ducts enter the body through the firewall. These openings can be seen in the image I linked to a couple of comments above. I’ll add a bit more detail to this post in a couple of days to hopefully clarify. I’d be concerned as to where this water is coming from as there obviously shouldn’t be any there?
Hope this is of some help … Cheers
hi thanks for reply i also found a diagram showing seals 15 and 17 the vent ones are not made now so i’ll have to sort thx again nick
I used old wetsuit and cut the shapes, glueing with contact adhesive. Works great
Thanks for the helpful instructions and clear photos. I was pouring over 3 different sets of instructions with very unclear B&W photos for the heater upgrade, when in confusion I came across your blog. Extremely helpful, thank you, and an inspirationally clean workbench :o).
Warm Regards from across the ditch (Tasmania),
Thanks for the feedback and I’m pleased you found the post useful. I can assure you that normal service has been resumed and my workbench is currently a mess!
I plan to buy the studs (from SNG) with rubber isolators used in 3 places to mount the heater case to the firewall. As all of the seals between the case and the body of my car were destroyed, I will be using weatherstrip or other material to replicate them. Can you tell me how thick the foam between the case and firewall should be to match the thickness of the rubber isolators and allow for some compressions for a decent seal? Also, the foam between the case and opening in the plenum. Thank you.
I have a new fan seal which is 11 mm thick, I assume the heater body seal will be the same size. I’m not sure about the case to plenum seal, that might be thinner, probably the same as the lip on the heater base. My heater is packed up as we are moving so can’t check further. I hope this helps.
That information is great. Thank you. Good luck with the move!