The 'E' Type Forum

My baby is now showing very high oil pressure constantly after start, 80. Using a test gauge their has confirmed the dash good reading to be good. The realease valve has now been replaced but the problem is still the same . Any thoughts guys ??

Others report that the big relief valve caps the pressure at somewhere between~70-90psi and that is what you are reporting, so why is this "very high" and what exactly is "the problem"?

kind regards
Marek

That's exactly the oil pressure my XJS has cold.

And have you changed anything? Is the gauge still being supplied an average 10V from the voltage regulator? Is the sender the correct type, with twin lugs in the centre? If the gauge is being supplied 12V (= 13.6V) and the sender is the type with single lug on the side, rectify both of these, should be ok.

lowact wrote: ↑

Thu Aug 18, 2022 10:52 pm

Is the gauge still being supplied an average 10V from the voltage regulator?

This may become a point of confusion.

The circuit diagram shows the gauge and sender are supplied by a non-regulated green wire supply. This is because the original senders were of a bi-metallic strip construction. In effect, they had their own built in voltage regulator and the oil pressure signal floated on top of this. An old style sender like this makes an LED "strobe" on and off rapidly if it is fitted as a substitute for the gauge.

It is also possible to buy replacement senders which are simply resistive in nature, just like the fuel level sender is. An LED fitted inline with one of these would stay solidly illuminated if fed by the same white wire.
The (resistive) fuel sender circuit is fed by a green/black wire from a regulated supply.

Another way to differentiate the sender type would be to simply hook up an air compressor to the sender and bench test it on its own. The resistive sender will vary in resistance (between the lug and the case) in proportion to the air pressure, but the old bimetallic type of sender won't.


Cold oil is thicker (more viscous) than warm or hot oil. That's why oil pressure on a cold engine is high. The relief valve caps this at its pop-off pressure. It's reasonable to expect the working pressure to drop below the pop-off valve value once it is both warmed up and revs are low. A freshly rebuilt engine with new bearings typically has a higher oil pressure than an old engine.

I wouldn't consider oil pressure to be "high" unless it is higher than the cap value.

kind regards
Marek

If this was my engine, then unless I had a very non standard oil pump or the crank had been fitted with bearings that were exactly the same size as the crank ( ie no clearance for any oil), I probably wouldn't have 80 psi oil pressure. I would have a faulty oil pressure sender.

I already have several faulty oil pressure senders. They are a thing, not a myth.

I get 70-75 when cold on my series 2. Accurate, as measured in a workshop on a capillary type guage and now on my fitted mechanical guage. Runs at 65 when hot.

80psi (full scale) on a cold start is quite normal and is what my unrestored V12 has always shown for the last 50 years!
However, last year I had the engine out and took the opportunity to install a 'wet' mechanical gauge.
The new gauge is scaled to 100psi and the engine still records 80psi on startup; no change!
When fully warm it records 25 to 30psi. at idle and circa 65 at 3000rpm.
Cheers

Dear All,
My unrestored 47K miles has 70psi cold started on choke, 20 psi warm on idle and 60-70 warm motoring.