Rising Oil Pressure?

[Yatesy350i]

Hi All

I took the 350i for a little warm up run yesterday just 5 or so miles as she's not been out for about 5 weeks. Noticed the oil pressure gauge was erratic when lifting off. Acting like a windscreen wiper! Just been out for another quick blast and it now seems worse. Not only do I still have the erratic gauge on lift off. The reading also rises significantly as the revs rise. Almost hitting 5 before I noticed. This can't be a good sign. Any ideas? Oil pressure is normally between 2-3 all the time. Oh car was well up to temperature before putting my foot down.

Cheers Karl.

[adam quantrill]

It might be that the pressure relieve valve is stuck shut. Normally this would open at around 35psi or 3 bar.

You can get at it under the front of the engine without taking anything else off. First a spring will come out then the valve which is a cylinder with the far end closed. It might just need cleaning off and refitting.

If it's stuck fast you might need a threaded thing e.g. a bolt to get in the open end and engage with it. Or else the lid of the oil pump will have to come off.

Also on the 350i I have noticed a small rise on lifting - maybe 1-2 psi, only when hot, this might be nothing to worry about.

[Yatesy350i]

Thanks Adam

I'll have a look at the PRV one night this week and report back.

Cheers Karl.

[wild rover]

Had a similar problem which was traced to the sender unit.

[Yatesy350i]

wild rover said:

Had a similar problem which was traced to the sender unit.

Yep I think you are right. Luckily I have a friend with a 390se who probably won't mind me stealing his sender unit for a bit of fault finding ;-)

Cheers Karl.

[Yatesy350i]

Right Gents

I got around to looking at this today. Cleaned out all breathers and the oil PRV. Replaced the sender with a known good one. The erratic nature of the gauge on lift off has disappeared. But the oil pressure still matches the revs from 3k up all the way. So I suppose the next step is to change the gauge or fit a capillary fed gauge for testing. Has anyone got either of the above I could borrow please? The car has never done this before last week. Oil pressure always between 2-3 no matter what?

Is this something I should be worried about? What oil pressures do other 350i owners see?

Cheers Karl

[adam quantrill]

It will cause excessive wear of the cam end gear and/or dizzy gear if the revs are sustained with the pressure above 4, but other than that you can drive it and keep the revs below that point.

[colin mee]

Hi Karl. I will start mine and have a look for you.working away till then.colin

[Yatesy350i]

Thanks Gents

[colin mee]

Hi Karl. Hope this helps.I changed my gauge and the sender to a pipe one.so should be more accurate

[adam quantrill]

Is that sticky back plastic? ;^)

[colin mee]

Yes.that's my next job

Edited by colin mee on Friday 24th February 19:11

[gmw9666]

adam quantrill said:

Is that sticky back plastic? ;^)

Nowt wrong with a bit of sticky backed plastic lol

[colin mee]

Not looking forward to it.been putting it off for year's. To many wires to disconnect

[Yatesy350i]

Well I replaced the electronic gauge with a temporary hoes fed gauge in place of the sender and sadly it confirmed that the oil pressure does deed flow the rev range from 3k upwards. So 5000rpm = 5bar.

Had a chat with V8 Developments and several others and the general census seem to be that a cam bearing has probably turned and blocked or semi blocked one of the oil ways.

V8D have offered to rebuild it or build me a 3.9 as a direct replacement.

Looks like I may be a passenger at this years Fest :-(

[adam quantrill]

Hmmm - let's say one cam bearing has rotated, that's one oilway and that leave 4 other cam bearings free.

Plus there are oilways into both heads for the rockers, not to mention the one(s) that go into the crank bearings.

I don't see it myself - one rotated bearing in itself won't be enough to produce this effect, surely?

Let's have a few more theories chucked around....

It might be worth trying a "tadpole" style PRV first before giving up hope.

[The Hatter]

I'd be very cautious in responding to diagnoses from a distance (mine included!). I'd also think that high pressure is not a problem as such, it'll put a significantly larger load on the cam/distributor/oil pump drive but otherwise is not an engine destroyer. The hydraulic lifters may do some strange things but if the engine is otherwise running OK then I'd carry on running it until the 'problem' manifests itself in some other way. Especially if you're looking at an engine rebuild/replacement anyway!

Where exactly is the oil pressure gauge plumbed in to?

I'd place a bet that it's something to do with the remote filter or the oil pressure relief valve/spring.

The TVRs have a remote oil filter that has a one way valve in it. I wonder if the remote filter block is connected the wrong way around?

I think the oil pressure relief valves have a reputation for sticking, that seems the most likely cause to me. It's easy enough to take it out and see if it moves freely; and as Adam says there are tadpole valves out there for exactly this problem.

[KKson]

Early days with my 350i I was getting variable oil pressure when it revved. It took all of 10 minutes to change the oil pressure relief valve and all was good. I did had issues with lumps of sludge also blocking the oil pressure sensor and warning switch as the car before my time had not been used much in the previous 5 years. I removed the various connections in the area, cleaned them and gave the engine a thorough engine flush and again normal service was resumed. It would certainly be worth trying a further investigations first before shelling out a load of cash on an engine swap.

[ElvisWedgeman]

Totally agree. Erratic reading on the oil pressure gauge doesn't nessesarily warrant an engine rebuild. There are many things that it can be. I hear your saying that the pressure reading is real, but the cause could be something simple. Further investigation required in my opinion.

Have you changed the oil filter preferably a different type?

Tony. TCB

Edited by ElvisWedgeman on Friday 14th April 10:50

Edited by ElvisWedgeman on Friday 14th April 10:53

[mrzigazaga]

Yatesy350i said:

Hi All

I took the 350i for a little warm up run yesterday just 5 or so miles as she's not been out for about 5 weeks. Noticed the oil pressure gauge was erratic when lifting off. Acting like a windscreen wiper! Just been out for another quick blast and it now seems worse. Not only do I still have the erratic gauge on lift off. The reading also rises significantly as the revs rise. Almost hitting 5 before I noticed. This can't be a good sign. Any ideas? Oil pressure is normally between 2-3 all the time. Oh car was well up to temperature before putting my foot down.

Cheers Karl.

Hi Karl

Could be a faulty connection to the gauge?...I know zero oil pressure is not good but as said be very careful in arriving at assumptions based on random possibilities..Check the connections and resistance on the gauge...Check the sender connection...When was the oil and filter last changed?...What type of filter do you have on it?....What oil do you have in there?...Hopefully its a simple fix...

Cheers


Ziga