E type 3.8 oil pressure

[cactusman]

This may be of interest to anyone having oil pressure gauge issues. After a month of standing I started the "E" last weekend. Usually the oil pressure gauge moved leisurely to about 40 PSI on cold idle. Last week it barely made 20! I took it for a drive where it got to about 30 before slumping to zero. I did not panic as I also have a 15 PSI switch and light fitted and the light did not come on. I presumed a sender issue as the senders are notorious so I changed it. I got a new one from a reputable source which was even an original Jag part. New sender fitted. Cold idle - barely 20. Driving when warm barely 20!. I started to assume the bypass valve had stuck so removed and cleaned. No evidence of foreign objects. On re-start the same low pressure. At this point I began to assume the worst.....major engine issue.
As a last thought I removed the gauge and connected to the old sender which I attached with some hose to a bicycle pump. Pressurising to 40 PSI on the pump gauge the electric gauge moved to barely 20PSI. I upped it to 60 PSI on the pump. The electric gauge slumped to zero. Dead sender. It was an old bimetallic sender so measuring the voltage across the gauge you should see it rise to 12 and then drop to zero as the contacts open and close. At 40 PSI it did - just - but not at 60. Now I removed the new sender and did the same thing. The new sender is NOT bimetallic as the voltage across the gauge is now continuous and between 2 and 4 volts depending on pressure. Higher pressure = lower sender resistance = higher voltage across the gauge. However at 40 PSI on the mechanical gauge the electric gauge showed barely 20 with the new sender.
CONCLUSION = NEW senders are proportional resistance senders and NOT bimetallic ON/OFF senders and seem not be correctly calibrated for an old gauge. You CAN adjust the calibration of the gauge - there are two waxed off holes in the back through which a small flat blade can be used to adjust the zero and full scale deflection. After much testingand fiddling with my bicycle pump I got my old gauge to read zero at 0PSI, 20 at 20 PSI, 40 at 40PSI and 60 at about 55 PSI - pretty close. Re fitting the gauge and new sender I now get almost 50 PSI indicated when cold falling to 40 when warm at 1200 RPM. Not the engine at all but a combination of dud old sender and new sender not matching old gauge!!!!!!
So if you replace your sender BEFORE YOU DO, remove the gauge and use a 12 volt source (circuit is in the workshop manual but is dead simple - wire the gauge and sender in series across 12 volts) and bicycle pump to check your new sender and old gauge are actually matched. You may well find they are not and avoid endless panic when you think you oil pressure is wrong!!!!!!
Happy E ype motoring......Julian Cooke

[1954Etype]

Better still, fit a mechanical gauge and you can reliably see what the true oil pressure is!

[cactusman]

That would of course be the ultimate solution...I do have a pressure switch and LARGE light in case of bad stuff happening.

[PhilBell]

My 3.8 oil pressure is all over the place even when motoring at steady motorway speeds so priority is to check the true oil pressure. Any advice on which wet gauge to buy, fittings required and where to plumb it into the engine?

[JEP41]

Hi Phil,

MC Wilkinson in Doncaster, I purchased two off him many years ago and they are still working perfectly one in my e-type the other in my MK2. I believe the enthusiasts club also sells them.

[JimmyS]

Any advice on which wet gauge to buy, fittings required and where to plumb it into the engine?

http://www.etypeuk.com/forum/viewtopic.php?t=173