Oil pressure drop

[ehos]

My oil pressure is dropping progressively as I drive the car
Startup with choke = 45 to 50 psi @ 1200 rpm
Slightly warm 10 min drive 30 psi @ 800 rpm and 40 psi @ 2000 rpm
Warm after 30 min drive 15 psi @ 800 rpm and 35 psi @ 2000 rpm
After driving hard and revving the engine multiple times to 4500 = 5 psi @ 800 rpm and 30 psi @ 2000 rpm
Note that:
63 FHC with 4.2L tri carb
Engine was rebuilt with 2000 miles on it
Kendall 20/50 oil
Brand new jaguar oil sender unit

Should I be concerned? Is this normal?
Thanks

[christopher storey]

Certainly this is not something I would ignore, particularly with a newly rebuilt engine . The electric gauges, however, are notoriously inaccurate particularly from the point of view of the sender. The first thing to do is to borrow/buy a mechanical pressure gauge and plug this into the oil gallery which runs at filter level along the right hand side of the engine , and see whether these are genuine pressure readings. If they are, then the next thing is to change the oil filter element and see if this alters things . If that produces no improvement, then sump removal and checking of the oil pickup pipework and of the oil pump is next in line

[ehos]

Thanks Chris, I will get a mechanical sending unit, do you know the adapter I need to use, is it 1/4 in BSP?

[christopher storey]

I'm afraid I don't know the thread although it could well be BSP although I would have thought it's bigger than 1/4 inch . If you take one of the gallery blanking plugs with you ( There are 3 or 4 IIRC ) it should be possible to match it

[64etype]

Thanks Chris, I will get a mechanical sending unit, do you know the adapter I need to use, is it 1/4 in BSP?

Don't know the thread size for the oil gallery plugs, but the female thread on the oil filter housing is 1/4" BS parallel. The link below provides some info for plumbing a mechanical gauge to the filter block. There are also numerous related discussions on Jag-Lovers. Note that the bottom fitting in the photo is not correct....the thread in the filter block is British Standard parallel...not tapered. While tapered will work, it will screw up the thread in the aluminum flier block. For an in-dash Smiths gauge installation the simplest arrangement is a 1/4 to 1/8 BS parallel fitting (with 1/4 sealing washer), then a special 1/8 tapered to Smiths gauge fitting from one of the Mini suppliers, then the hose/pipe (Smiths connectors on both ends) to the Smiths gauge. I also added a 90 degree Smiths fitting at the gauge/hose connection to ease installation.

A suitable used mechanical Smiths gauge should be easy to find. The Sunbeam Tiger, some TRs and some Lotus models used them. The bezel might have to be exchanged as most of them are chrome. In the US, suitable hose/pipe and fittings are offered by Mini suppliers. A new aftermarket "Smiths" 0-100 mechanical gauge is offered by some suppliers, but I had very bad experience with them.

https://jaguaretype.wordpress.com/home/ ... ure-gauge/

[ehos]

Thank you so much Eric. This forum truly eases my fears as a new e type owner!

[Moeregaard]

Before taking things apart, I would verify that the sump is not overfilled. An excessively high oil level can cause foaming and a resultant loss of oil pressure. You didn't mention any strange noises, so it doesn't sound like a run main or big-end bearing.

As others have mentioned, accuracy is a "moving target" with the factory gauge and sender, so checking things with a manual gauge is essential in my view. When I rebuilt the engine in my '65 many years ago, I fitted a small, fluid-filled gauge designed for high-vibration environments to one of the gallery ports and simply left it in place. Going from memory, I believe the thread is 1/8 BSP (28 threads/inch), but I can't remember where I purchased the gauge.

[ehos]

Checked the oil, not overfilled and no foaming. The engine runs really well, no odd noises at all. Very smooth. Ordered the parts to fit both the mechanical gauge and the electrical sender at the same time. Will report back soon!

[marc]

Hi Eric (64etype)

what do you mean by "A new aftermarket "Smiths" 0-100 mechanical gauge is offered by some suppliers, but I had very bad experience with them. " ?
I bought mine from Holden in England last year and the indicator "jumps" sometimes, i.e. not progressing or reacting with a smooth movement, so I am only half-confident. What were your problems with these Smiths mechanical oil pressure gauges?

Best wishes, and thank you!

[64etype]

The one I purchased from a U.S. Mini vendor did the same thing. Further, it would not go above 30 psi on a newly rebuild engine. I removed and tested it on my air compressor by increasing air pressure in 10 psi increments up to 70psi. The gauge was definitely stuck at 30 psi. I initially replaced it with a Stewart-Warner, which read 65-70 psi on start up. Then found a "genuine" used Smiths mechanical gauge from an old Lotus on E-bay. Returned the 0-100 psi Smiths knockoff for a refund.

[ETTony]

It maybe 'stuff' in your oil pressure relief valve or the ballance valve.
Well worth removing the oil filter housing and cleaning these out.
This cured my low oil pressure issue.
Good luck.

[ehos]

After installing both the mechanical oil gauge and sender, my oil pressure was normal! Starts cold at 55 psi and drops to 35 psi at idle hot. Since I have a brand new OEM sender, must be the smith gauge. I’ve taken it apart and can see the adjustments, any advice how to calibrate it?

[Series1 Stu]

I wouldn't assume, just because the sender unit is new, that its any good. They do have a very bad reputation.

Regards