THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

I had a small filter fitted to the breather in lieu of the tube that runs from the breather to the air cleaner.
After a long hard run, sitting at around 70mph, I noticed a lot of oil on the inside of the bonnet and down the valley between the cam covers.
The engine is fully recon (meant to be !) and I've noticed lately that the oil pressure, which used to sit at 60 almost all the time, now fluctuates depending on the revs.
Any comments/thoughts please......

Oil pressure should fluctuate with RPM hot. As long as over 40psi totally warmed up at approx 2000RPM.

You seem to be building up crankcase pressure but with a modified breather it is hard to know if it's abnormal. Do you have the screen in the breather housing on the chaincase?

Make sure where the oil is coming from ~ breather or leaking gasket.

Make sure oil level in sump is not too high.

Compression test engine to check for ring blow by or do a complete leak down test.

Take breather back to standard or fit a breather catch tank.

Good luck!

is the filter open to atmosphere? or is it sealed?

If it is a sealed filter that's the problem. The gases must be allowed to circulate out of the engine, into the air intake where they will be ingested and exhausted.

Jose they do not need to go through the air intake and engine. The original Mk2 used to have a pipe from the block leading to a catch tank that needed emptying every service. You can buy a small oil breather filter to go on the engine breather pipe which is what I used to use on my racing Lotus Seven so the air going in to the air intake was clean air not dirty oily air.

well that is the way the factory engineers did it. I have to assume they knew what they were doing, right? When it comes to engine emissions stuff, I never try to outsmart the factory.

You are right that is the way the factory did it purely so the vented oil smoke and fumes from the breather would go through the engine where some would be burnt off and the rest out through the exhaust. Prior to this as I said with the Mk2 there was a simple catch tank where the fumes and oil smoke were vented in to. It was just a tin with the hose going into the top and it filled up with oil over time.
With modern filter systems you can just have a filter that the fumes go through and then when that is choked just like the catch tank you clean it or change it. With the filter system you are not sending dirty oily smoke filled fumes into the combustion chamber so the air is cleaner and the engine should run more efficiently and cleaner. We have been talking about the air intake vent hose and getting it forward of the engine and radiator to get cold air in to the system and then we have this oil breather putting hot air straight from the depths of the engine block straight into the combustion chamber. Mad really.
On my racing Lotus Seven we used to use the breather filter system so we had cool clean air not hot dirty air being burnt suggesting more power being produced.

We are trying to help a member with a specific problem & he has been given the correct advice!

I agree with Glyn's original post with the checklist. Do these simple things first and come back to us if the problem is not found and persists.

Thanks everyone - when I first had the car on the road the oil pressure sat at 60+ at any speed or revs, so I was most happy.
I did a compression check a few months ago and had 150 in all cylinders - I'll do another one when I have time.
The oil pressure now drops to around 10 at idle ! - not happy !
A mechanic I know said something about "blow by" ? and he suspects a problem in the bottom end.
Will keep in touch, but happy to hear all theories !

my XJ-6, (my first Jaguar), a 1984 4.2 liter fuel injected 6 cylinder, has an identical engine breather-to-air cleaner routing as the 1965 S type. This system was used until the last Series 3 XJ, 6 cylinder in 1987.

this tells me the factory system has been proven to work.

My 1997 Ford 4.0 liter fuel injected V6 has an almost identical engine breather-to-air cleaner routing too, the difference is the tube comes out of the valve cover.