SII FHC Oil Pressure drop

I’ve owned my car a little over a year now. My oil pressure gauge has always read 55-60. The last few times out I noted that the pressure was 40-50, but no issues. This eve, I noticed the pressure was dipping below 40 and close to home, read as you see below.:flushed: When the pressure hit the mark you see in the pic I felt a sensation like the car didn’t want to roll, RPM’s were fine but I thought the car stalled…I was near home and made it fine. I had no trouble revving or reaching speed. I check my oil often and the level is fine. Help…

First thing you want to do is verify that reading by plumbing in a mechanical gauge temporarily. Then check your oil level. If a problem is still indicated, take off the filter head and check the overpressure valve, which is what the return hose is attached to.Those are the easy steps.


A Good way to see if that is bypassing too much pressure, use a pair of hose clamping pliers on the hose: you will immediately know if that’s where the excess pressure is going.

Dont be fooled by the apparent ‘good condition’ of the brass valve: Tweety’s looked perfect, and replacing it solved my low OP issue.

As Mike indicates, Job One is to determine real OP, with a mechanical gauge.

I agree a mechanical check is the place to start, but may also be worth noting that (I think) Salvi recently had the instruments and other electrical dash bits out to install the wood panel.

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Correct, the gauge was out for the wood installation. Also, for about 10 minutes the gauge had too much current going through it (the bracket was on backwards), so was pegged at 60+, but I quickly put the bracket on correctly and the gauge was working and has been working properly. Also since the gauge doesn’t control oil pressure, rather measures it, it shouldn’t account for my experiencing a loss of power, no?

I wouldn’t trust these electrical gauges for accuracy. Changing to a mechanical operated gauge is on my list of improvements in the near future.

Would you explain please?

Yes I know, it’s sounds moronic and I shouldn’t have brought it up… I was rolling to a red light on an uphill grade and I experienced a sensation like my handbrake was on, it was a strange sensation. It very much could’ve been gravity and my paranoia knowing that my oil pressure gauge was trending downward. I, however, had no issues with RPM’s or pulling power.

20 psi is not dangerous to the engine, so it likely was paranoia.

True, but when your gauge has always read considerably more than that, a sudden change should be investigated, I’m sure you would agree. As others have suggested, time to install a mechanical gauge temporarily to find out the real numbers.

Absolutely, and I wasn’t suggesting otherwise: my only point is about 99 times out of 100 when you see a sudden drop like that, and it’s an electric gauge, it’s almost always the sender, and not the pump.

I did confirm and say that the first order of business is to confirm the pressure with a mechanical gauge, and also check the bypass by using a pinch pliers.

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Thank you very much guys. I will call my local Jag guy on Monday. This a.m., I started her up and the gauge read as I’ve come to expect (left pic). After 30 minutes of driving and back in my garage the gauge read as seen in the pic on the right. I paid attention to my RPM’s and pull, nothing to note while driving or at idle. Don’t know if this gives any further clues, but figured I’d mention it.

Are those both at idle? If so, I see nothing to be concerned about.

What weight oil are you using?

Pics of gauges (incl tach & temp) while driving at speed would tell a more complete story.

If oil pressure ever caused a loss of power, the engine would be irreparably damaged long before you noticed the power loss.

Acceptable oil pressure, warm engine, at idle, is anything over 10PSI. 20 PSI or so is typical. At 3000 RPM, 40PSI is typical. The rule is simple: 10PSI per 1000 RPM. Anything over that is gravy.

I had a problem with oil pressure dropping after warming up. Turned out to be debris (a piece of cotter pin) holding the relief valve open.

Talking about it doesn’t fix it. Check oil level, test with a mechanical gauge, check the over-pressure relief valve. Hopefully you find the problem and don’t need to go further.

The “parking brake” issue sounds like an unrelated problem with the brake system. If it persists and especially if it gets worse, start another thread…

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So, I had a few things done overall since the car was in for a look-see. I purchased differential oil (Castrol axle limited slip 80w-90 gear oil)[size=33px], gear oil (Redline MT-90 75W90 GL-4) [/size][size=33px]and engine oil / filter (Castrol 20/50), had all changed out. I ordered a sender unit and had the mechanic install it. When all was done, mechanic said he didn’t note anything out of the ordinary and stated in his experience, with a cold engine, the pressure is anywhere from 50+, then when warm, hangs around 25 psi at idle and 40+ at speed. I’m wondering if my oil pressure gauge was reading abnormal at always just shy of 60 psi and now reads normal and being reconnected with the addition of wooden gauge surround. :face_with_monocle: One thing I didn’t ask about was the relief valve… :flushed: I don’t know why he would not have checked the pressure manually, which I may call on Monday and ask him to do.[/size]

Plenty for a rolling idle. Have pulled and replaced the pressure valve as well. It’s not a big job.

On the Series 2 which the original poster has, the pressure relief valve is a self-contained unit, so it’s even easier to change. The problem is, the last time I checked they are unobtainable.

Not sure what you can do if it fails…

I believe aftermarket self contained valves are available, I located one each, on Welsh’s & Barrett’s websites.