Nissan too much oil pressure GU 4.2 turbo 1999 model @ 200klm

Is that hot , or cold pressure..

Mine will run to 80psi when cold, but soon drops when the oil warms up.. Hardly moves the needle on the gauge at idle w/- a hot engine..

If it's making those sort of pressures with hot oil, I'd say you have a sticking relief valve..

Yep, sounds like pressure relief valve sticking to me too.
I would use CEM flushing concentrate to give the inside a good cleanup after servicing the valve. If it has had oil changes with other than hot oil then I agree it could have sludge build up but the CEM will fix that.
No connection just a very happy user.
Ian

If it's a 3 Lt I wouldn't drive it till it gets fixed

Scoof,
The TD42 actually has 2x oil pressure relief valves, + an oil pressure regulator valve..
The problem could be related to any one (or all) of these:(

The oil pump relief valve is located at the rear of the block on the LH (passenger) side, under the turbo.. should be fairly easy to access this from under the vehicle, for removal/dismantling & cleaning..

The oil cooler (that's the alloy housing on RH side of block, to which the filters are attached) also has a pressure relief valve (top), and a regulator valve, which would be accessed from underneath if doing this in situ..
Removal of the oil cooler housing would also necessitate draining of the coolant...

I've not (yet) had to touch mine, so can't comment on ease of serviceing, but doesn't look like it would be too difficult to anyone who is 'handy with a spanner', though I'd strongly recommend having a w'shop manual handy..

I'm going to (respectfully) disagree with Ian on the need for a 'flushing concentrate' ... I know there are a few here who swear by the stuff, but...

IMHO (based on my experience), the very best errm, 'flushing oil' for any engine, is the correct spec oil for that engine, with the proviso that it (the oil) MUST be dropped while HOT, and immediately (within seconds, not minutes) after engine shutdown.. This ensures that all contaminants will be thoroughly mixed with the oil, and will be drained with the oil, instead of settling to the bottom of the sump pan only to re-contaminate the new oil...

In 40-odd years of serviceing all of my own (and a few other people's) vehicles, I have never seen the need to use any kind of a 'flushing concentrate', and I have never ever had a problem with sludge in any of 'em...

Regards, Ed C

In order for the pressure to go up - something has to be blocked within the oil system, would be the rational assumption.

Normally you'd look where the last hands touched it - i.e. maybe the last oil change?

Oil filters normally have a bypass valve, that - in the case the filter becomes blocked - it opens to allow the oil to bypass the filter, so that the engine is not damaged.

That bypass spring pressure setting has to be higher than the normal high oil pressure of the engine when running at WOT - which from your specifications was 65 psi?.

So - if the engines running at 85 psi - it seems as tho the oil filter is blocked (or it is not the right filter and the oil gallery doesn't line up with the entry to the filter properly)..

Example - did someone install the new filter with the plastic wrapping still intact across the face of the filter?

It would take a LOT of contaminant in the oil (water being the most likely) to block the filter and collapse the paper element which in normal operating situation would allow particles as large as 25 microns to flow thru.

Water however will saturate the paper element and allow it to collapse.

Oil in the water could happen from head gasket problems.

Quite simply changing the oil filter (for the right one) is the very first thing I would to to test for high oil pressure.

Next thing.

Bypass pressure - is there a large amount of bypass gas - such that when you remove the oil filler cap from the top of the rocker cover a lot of smoke escapes under pressure?

Being a turbo diesel - there should be a Exhaust Gas Recirculation system and probably a Positive Cranckcase pressure valve as well.

The positive crank case pressure relief valve should have a air inlet vacuum connection, that with increasing turbo revs, evacuates the crankcase of some of the bypass pressure, in fact lowering it with increasing revs - for the oil pressure to increase IF IT ISN'T THE OIL FILTER BLOCKED then you would think that this decrease in bypasspressure would help lower oil pressure unless all the return gallerys from the top of the engine to the sump are blocked.

That's pretty unlikely.

I'd almost bet my left nurry that the oil filters either blocked or the wrong filter - because the pressure it's operating at is the pressure required to activate the oil filter bypass valve.

Cheers