Thank you both of you as always extremely helpful.

I also spotted the corrugated aluminium air intake conduit modification in #19 compared to the 240 which has the same air filter box, that also looks like a useful cooling improvement.

Kind regards

 

I think MK1 cars took their inlet air via such a tube trom the inner wing, but it disappeared on later cars. It makes sense to me. We tune our engines on cold air with the bonnet open, then we expect them to run as well standing with it closed or crawling slowly in traffic when the air in there is at least at radiator temperature. It's very noticeable in V12 XJ saloons. They can have a difference in idle speed of two or three hundred rev/min between bonnet shut and bonnet open on a hot day.

 

Thanks Peter, I might look into options for the air circulation.

Just one more query regarding the overflow. Do you think the pressure rating of the radiator cap and the overflow caps of any significance in the expander tank modification?

 

I think the caps on mine were both 4psi or both 7 psi*. I'd avoid having the overflow cap of higher pressure rating than the radiator as it might cause some of the water to spill rather than go to the overflow tank.

*Sorry if I seem a bit vague, but it's a while ago and my Mk2 is largely dismantled at the moment.

 

.. on the subject of water spilling out of the radiator instead of going to the overflow: some suggest that you should use a very thin rubber washer to seal between the upper lip of the radiator and the rad cap. Mine was fine without it; smooth brass on brass sealed well enough. In the event of water squirting out of the rad cap, rather than adding a seal, I'd try a lower pressure cap on the overflow and also make sure the overflow tank isn't too full, it's enough to have the open end of the inlet pipe a bit more than covered when the system is cold.

 

Cold




Hot

 

Glyn's pictures show exactly how it should work. The pressure cap in his top photo has the rubber seal that mine seemed to work fine without.

 

You must just have been achieving a very good cap to radiator seal.

 

I was trying things out with what I had available and expected a leak. However, the caps are quite tight and the brass surfaces are very smooth. The low pressure of the Mk2 system may also help as the pressure in the radiator is trying to lift the whole cap (as well as open the outlet valve). The rubber seal might be more important for a modern system with 15 psi.

 

I've settled on a 7lb cap ~ probably because my new 4lb cap did not work at all. It was badly manufactured ~ Barratts replaced it FOC. Modern pressures I've been told are too high for the XK water pump seal.

 

Yes, the original seal lifts at a modest pressure. Unless you want to operate the engine at modern temperatures, 7psi is OK. Later water pumps (I don't know if that includes replacements) have a revised seal and run to 15 psi.

 

Both the caps on my system are 7lb and not had a problem.

The cool air system pipe was standard on the Mk2 and S Type up until 1966/67 when it was deleted for some unknown reason. My car being September 1967 did not come with it but I retrofitted the system. I used the Alloy corrugated pipe as I felt this would keep the air cooler as it runs over the top of the exhaust manifold where as the original pipe was made from corrugated paper. There is a clamp that was standard that attached above the generator to the block and this holds the end of the pipe at the back of the radiator. In my mind this seemed to be the wrong position as you were getting hot air going through the radiator into the pipe which defeated the object. I have channelled mine to the side of the radiator so I am mainly getting cooler air straight from the front grill. As Pete says the Mk1 had the pipe going through the inner wing into the wheel well but this would send a lot of dirt through the system which is possibly why they re routed it in the engine bay.
I fitted an alloy trumpet to the end of my pipe work just to keep it neat and tidy.


Alloy trumpet shaved on one side to sit against the inner wing.



And of the pipe showing the route beside the radiator and the bracket to hold the pipe in place.



Parts book diagram of the S Type air intake system.

 

yes, it appears that for a time in the late 40's to mid 60's (?) some designers, must have thought that air introduced into the induction system was deficient in some way if sourced from inside the engine bay. and so ducted air in from outside. over time, like kilties on golf shoes, they were often deemed superfluous and so removed.

 

Ideally induction systems require cold, more dense air.

 

I think most Mk2 cars with a paper air filter, certainly mine, have the Cooper's frying pan air cleaner. An item carefully designed to hide the cam covers and take air from the top of the engine bay, where the hottest air most likely collects.

 

Yes ~ Jaguar did some dumb things.

 

yes, lovely things, those. akin to hiding a woman's attractive figure with a moo moo ...if you remember what those are.

i figure they needed that space for something or other.

 

Barretts said to me that the genuine replacement part that was available at the time I ordered C15694 seal could not cope with 15psi. Now only aftermarket units available. They might be able to handle higher pressures.

 

Great information, thank you. Might need to consider the air duct modification as a subsequent project.

 

I like your smart inlet pipe.

Because I was going for concours I used a very close to original inlet pipe. Prior to cutting to length. A friend brought it out from the UK without a mark on it.