I cut into my oil pressure sender todayday, mostly to see how it worked, and with the slight hope of repairing it.

The first photo shows the sender with the guts more-or-less intact. In the dead center (hidden by shadow) is a metal cylinder the presses up on the hinged plate that is tilting slightly to the left. As the hinged plate responds to pressure, the small arm (to the left) moves up and down against the coil. As the small arm moves up and down, it rubs against the wire (which I pulled off, you can see it attached to the terminal near the top of the coil) that is wound around the terminal, presumably changing the resistance. As is common apparently, the thing was full of oil.

The second photo (in situ) shows what's left when all the other stuff is stripped off. There appears to be a copper pressure vessel (similar to that in an anaroid barometer) that flexes as the oil pressure increases and decreases. This causes the metal disk in the center to move up and down, pushing on the hinged plate shown in the first picture.

If I had to bet, I'd say that some manufacturing defect forces the press-fitted top assemble down a bit too hard on the bottom assembly, stressing the copper pressure cell and producing the leak.

So...that's the result of staying at home during our first blizzard of the year ). If my theory is bad, someone correct me. I'm just guessing about how all this works.

Thanks,

John
1987 XJS V12, 62,000 miles.

 

Good photos. The description of the mechanism sounds accurate, but the cause of failure "manufacturing defect.." doesn't sound right unless this was a new sending unit. If this was the original, fatigue in the bellows & cracking seems more likely. I just replaced the idiot light sending unit in my 1988 which had a leaking diaphragm. Much less expensive than the pressure sending unit.
Unfortunately there is a "designed life" in many mechanisms & there are good examples of that.

 

Good point...why would I expect anything to last 25 years!

Now I have to find a substitute for it. Something that looks amazingly similar was $195 + shipping from my local auto parts dealer...too much for my taste :-)

John
1987 XJS V12, 62,000 miles

 

See my reply to your second post.

Rock Auto

BECK/ARNLEY Part # 2011505

bob gauff

 

Just ordered one Bob, thanks!

John

 

Ebay seems flooded with these pressure senders, now at 22 dollars:
http://www.ebay.com/itm/WD-Express-802-26055-738-Oil-Pressure-Sender-or-Switch-/350817105707