Bad oil leak - possibly from Oil Sender/Warning Light Switch(es)?

[Redman]

Sudden oil leak; have not been playing around with the engine so nothing I have done. First noticed clouds of oily smoke after accelerating onto a motorway; then copious trail of oil on coming home and parking. On further inspection, smoke is from oil on hot exhaust; but cannot see where leak originates. Engine looks clean and dry enough from heads down. Very difficult to see exactly what is going on, but does look as if oil pressure switch and/or the oil warning light switch are either the source of the leak or are also being dropped into. Engine above switches looks dry (however no real line of sight into what is a very tight area). But amount of oil on exhaust (and floor!) seems too much to be just a weeping switch at fault ...... Could this really be the problem? Common? If I can get my hand and a tool in there I'll try tightening (torque?) but I don't have a ramp so difficult enough! Thanks in advance for any ideas ) advice.

[Redman]

PS: when opened bonnet to look for issues, found the crankcase breather "valve" (the rubber connecting boot) had come loose. Not sure if this was because only held on with zip tie or whether excess pressure present. However both the connecting tubes and the metal gauze oil trap were clean as a whistle so perhaps conincidenal? Thoughts?

[DWW]

It will e difficult to find the source before you somehow got her up in the air and sprayed brake/carb cleaner to clean the leaked oil as it would have sprayed everywhere during your journey. Only then you stand a chance to pin point the source.

[jfmassa]

When you get the opportunity to inspect the area you suspect, also check to the right, the oil banjo fitting and the pipe itself. The oil feed pipe (C37764) has 3 fittings, which could leak, and the pipe could also fracture.
Good luck!

Joe

[MarekH]

Oil isn't going migrate either or forwards, so start at the front and the top and run your fingers across all of the joints and components bolted onto the block. If you are lucky, and I think you will be, everything in front of and higher up than the rear main seal will be dry.

The crankcase breather valve on the front of B bank which plumbs into the manifolds is designed to draw air and any crankcase oil vapours into the manifolds and put the crankcase under mild vacuum. In the absence of crankcase vacuum, any blowby gasses, instead of being drawn back into the engine, will now exit and push oil out wherever they can. Amongst the ways oil can now be pushed out, other than through any gasket or straight out of the now loose breather, would be out of the rear main seal.

If I were Sherlock Holmes, I'd first ask how does a big rubber dome thing the size of a tennis ball which is ziptied onto the B bank engine breather get to come off all on its own? The answer, Watson, is that the tubing going to the manifolds is 100% blocked up and so the build up of blowby gases increased in pressure inside the crankcase, blasted oil out of any orifice it could, either blowing out gaskets or pushing past the rear main seal. Pressure then got sufficiently high that the B bank breather valve cover blew off, which is how you found it.

Conclusion? Remove the tubing between the B bank breather and the carburettors and clean it out so your crankcase breather draws that oil back into the engine, not blast it out through the rear main seal.

kind regards
Marek

[chrisfell]

Someone with better knowledge may chime in, but I thought that early V12s had a separate oil pressure warning light switch low on the LHS of the block, directly over the exhaust pipe. I have known of one other case where this switch fractured sending oil straight onto the exhaust pipe.

[MarekH]

I have known of one other case where this switch fractured sending oil straight onto the exhaust pipe.

That sounds very sensible. There must be a reason why they moved the senders from under the exhaust manifold to up top. They obviously get toasted down there.

kind regards
Marek

[Redman]

Responding to Marek's final point (Conclusion? Remove the tubing between the B bank breather and the carburettors and clean it out so your crankcase breather draws that oil back into the engine, not blast it out through the rear main seal.):
On finding the BV had come off, I disconnected the pipe going into the breather valve rubber piece and blew through it to check for blockage - seemed clear and certainly easy to blow through. Or do I need to dismantle and check each part of the piping separately? Regards - and thanks for the advice.

[MarekH]

If the pipe is blocked, it'll be blocked where the tubing is at its thinnest point, not at the single broader tube. That means you'll have use some engine degreaser to dissolve out any solidified residue in the thin 1 to 4 tubing and then blow that out before refitting it.

You never mentioned what your oil pressure was. Pumping oil straight out of the oil gallery is obviously a very bad idea. A more likely scenario was excess oil sloshing out of the sump through the rear main seal because of pressure in the crankcase.

You still need to work out where the oil was getting out to decide which is which but the breather probably didn't fall off on its own. The joints in the senders are obviously supposed to be good for over 70psi and wiping them over with a clean tissue ought to tell you whether they are dry or not.

Also, what's the significance of the 18:01 photo in the first post? Have you sealed this up with a blue jointing compound on top and white PTFE tape underneath? This seems at odds with your saying access is poor or is this just a stock photo of someone else's car to confirm that yours is an earlier car with the senders under the left rear exhaust manifold?

kind regards
Marek

[Redman]

Many thanks to all. Oil Warning Light Switch appears to have failed: all my crawling / feeling around under the car and engine came up with little or nothing - all pretty clean including sump area. So started her up and immediate oil leaking. Had to get under the car again (on axle stands) which wasn't pleasant given the hot oil and hot exhausts(!). See photos before and after.

[Redman]

So (fingers crossed) a new switch will sort things out. But I have been reading on this site about advantages of converting to a mechanical oil pressure switch etc and at the same time getting things up on top of the engine rather than in the incredibly difficult area they are in currently (early S3). Do the kits simply tap a new steel line into the current access plate/ drilling? The ones I've seen here seem to show 3 oil lines ..... How do I plumb all this in, or are the kit instructions usually fail safe?

[Redman]

And in reply to Marek's kind advice: all crankcase breather tubing removed and checked. All clear (though I used some brake cleaner on them anyway just to be doublyvdure) so perhaps the valve coming off was indeed a coincidence. I hope so! And yes, the photo of the switches was a stock one taken from another post when I was doing some initial homework. Thanks again. Very patient!

[MarekH]

That's a good result. Near zero maintenance work and near zero cost.

With luck, the new oil switch will be good for another 40 years, so there is no pressing hurry to replace anything. Later cars had a blank plate where your senders are. Instead, the oil line leading up the the cams joined onto a little pedestal at the back of the "V" and the senders were relocated there. It's probably more work than it's worth to get hold of a second hand part from a later v12 unless you also want to fit a mechanical gauge. One of the very first test cars, a press car, had a second sender fitted on an oil gallery plug at the front of the block. They obviously couldn't find anywhere easy to mount one either.

kind regards
Marek

[Redman]

Well my guage reads a constant 80 - cold / hot /idle / full throttle - so will try replacing pressure switch as well while I'm at it.

[christopher storey]

So (fingers crossed) a new switch will sort things out. But I have been reading on this site about advantages of converting to a mechanical oil pressure switch etc and at the same time getting things up on top of the engine rather than in the incredibly difficult area they are in currently (early S3).

By a curious coincidence, there is an article by David Marks in the new ( July 2023) JEC magazine which arrived with me this week dealing with fitting mechanical pressure gauges to each bank of a V12 XJ Coupe ( pages 70 to 73) underbonnet , one mounted on the brake pedal housing and one to the bonnet latch housing ) as means of cross checking the electric in-dash gauge

A bit complex , not to say expensive , but it might give you a guide as to what is involved

[Redman]

Thx. I'll have a look when it arrives.

[Redman]

6 hours to get both oil pressure sender (easier of the 2) and oil warning light switch (what a b******!) out and replaced. Satisfying once done, but not something I'd wish to repeat in a hurry. On the plus side, my oil pressure switch now moves around in line with what one would expect; and neither appears to be leaking. Result.