Oil pressure too high !!

[rbryant]

Hi guys, wonder if anyone can diagnose this problem ....

... my oil pressure is behaving strangely today, reading about normal at tickover but climbing off the scale as soon as the revs are over 1000 and staying there. Electrical or real do you think?

Any experience or suggestions most welcome - the car runs normally and seems fine in all other ways.

[CaptiV8ed]

There's only one thing you can do, and that's take out the pressure relief valve and give it a clean. They can stick, causing over pressure. As the reading is going off the scale, let's hope it's electrical. Although, if it's reading right ar tickover, that MAY suggest that the sender is working correctly. If you have a serp engine, the relief valve is on the offside of the timing cover, below the oil pressure warning light switch. If you have a pre serp, I can't answer that right now, I'll have to see if there's anything in the book.


At the risk ff egg sucking training, the prssure relief valve is siomply a piston in the casing with a spring behind it. All simple stuff, but if they get dirty, as they're such a close fit they can sieze.

Hope this helps,

Nick

[CaptiV8ed]

Had a lookin the book, both sero and pre-serp valves are locagted just above the oil filter. I believe the piston and spring is held in by a circlip.

[spend]

Its on the oil pump base on the pre-serp facing towards the crank. No circlips on mine..

Be very careful, unbeknown to me I had an 'uprated' spring arrangement and after upgrading to nice oil had super pressure. Unfortunately 50psi seems to be the limit of the crank oil seals in particular and you really dont want to blow the rear seal....

Dave

[rbryant]

I was in Dorset when this happened and drove back gently to Bromley - I am going straight to the garage in the morning though, thanks for the advice and fingers crossed.

[Tahiti450]

spend said:

......... Unfortunately 50psi seems to be the limit of the crank oil seals in particular and you really dont want to blow the rear seal....
Dave

Just a note to clarify -- the oil seals are not exposed to pressurised oil, they simply seal the crankscase and operate at crankcase pressure, the only time they could blow out is if there is severe crankcase pressurisation, usually due to some catastrophic failure (piston etc). The system oil pressure will not affect the seals.
The main issue with excessive pressure is that this can cause pump-up of the tappets and can in fact stop the engine. I found this out by chance many yaers ago when experimenting with packing the relief valve on my Rover P6b to increase oil pressure and had a situation with pressure going off scale followed by the engine misfiring and stalling as the valves were all prevented from seating. Therefore, if the high reading is genuine, and given that the top reading in the TVR is 90 PSI (Rover P6b is 60PSI) i would expect the engine to stall or at least misfire as compression is lost (unless there is virtually no preload on the tappets, which is very unlikley).
A few weeks ago my oil pressure gauge went mad - swinging from normal to off scale and zero as going on and off throttle. Examination of the sender unit revealed a broken resistance winding on the rheostat. Off scale readings indicate that the sender resistance is very low or shorted. I think this will turn out to be a sender problem, or the wiring to the sender which is very vulnerable to hardening and cracking of its insulation.

[ray_von]

Tahiti450 said:

spend said:

......... Unfortunately 50psi seems to be the limit of the crank oil seals in particular and you really dont want to blow the rear seal....
Dave

Just a note to clarify -- the oil seals are not exposed to pressurised oil, they simply seal the crankscase and operate at crankcase pressure, the only time they could blow out is if there is severe crankcase pressurisation, usually due to some catastrophic failure (piston etc). The system oil pressure will not affect the seals.
The main issue with excessive pressure is that this can cause pump-up of the tappets and can in fact stop the engine. I found this out by chance many yaers ago when experimenting with packing the relief valve on my Rover P6b to increase oil pressure and had a situation with pressure going off scale followed by the engine misfiring and stalling as the valves were all prevented from seating. Therefore, if the high reading is genuine, and given that the top reading in the TVR is 90 PSI (Rover P6b is 60PSI) i would expect the engine to stall or at least misfire as compression is lost (unless there is virtually no preload on the tappets, which is very unlikley).
A few weeks ago my oil pressure gauge went mad - swinging from normal to off scale and zero as going on and off throttle. Examination of the sender unit revealed a broken resistance winding on the rheostat. Off scale readings indicate that the sender resistance is very low or shorted. I think this will turn out to be a sender problem, or the wiring to the sender which is very vulnerable to hardening and cracking of its insulation.

Can anyone else confirm who is right? I thought Alan is but Dave is usually right as well. Anyone?

[spend]

I am not infallible Ray.. My most informed source is of the same opinion as Tahiti - yet I still have reservations. The important point is that extremely high oil pressure is not automatically a good thing.

Dave

[ray_von]

Cheers mate

[GreenV8S]

I don't see any way for high oil pressure pressure to blow crank seals, but excessive oil pressure will shag the oil pump drive which is really bad news.

[StardustV8]

Are these cars fitted with positive crankcase ventilation valves?