oil pressure

[bigherb]

The WBX in English.
Don't get too hung up on pressure alone, the balance between volume is important too.

[itchyfeet]

Thanks bigherb
and in English too

I agree with the volume statement which is why I don't think pressure will suddenly drop when the bypass piston cracks open against the spring, I think it will need to open quite alot before enough volume of oil will flow to reduce the pressure significantly.

[bigherb]

If you have a later engine with two oil pressure switches you can have a play and answer your question.

But figures using multigrade oil are meaningless apart from as a comparison you don't know what the oil rating is at the temperature you are checking it at. Oils are only rated a two temperatures it is what happens in between and past those two temperatures is important. mono grade oils are more stable, a SAE 30 may well be be thicker at higher temperatures than a mineral 20W50 but may be thinner than a semi or fully synthetic.

[itchyfeet]

Spent a few hours this dull and wet afternoon in the shed splitting an early DG ( engine on the right is late DG) to examine the oil feed system in detail with a torch and a piece of wire to check where the drillings all go.
Very interesting

Some bit's I still don't fully understand like how the crank pulley bearing oil channel is drilled and cast , the diagram above may be technically correct but does not describe it well, I feel an itchy diagram coming on.

Pressure relief valve vents to oil pickup pipe and not sump that's for sure so my oil temp sender is not in sump oil.
High pressure switch is in the end of the main gallery after oil filter
low pressure switch is in a lower drilling off the main gallery feeding camshaft so may suffer some pressure drop if tappets or cam bearings are worn, I'm thinking a pressure check on the high pressure switch location ( main gallery) would be very interesting to compare.

[silverbullet]

I think the second oil pressure switch is more a sign that VW had run out of places to put things by then!

[wizwilson]

be interested to know what sort of pressure difference there is between the 2 switches, when you going to do the test ?

[itchyfeet]

I'm interested too but getting guage into the high pressure switch is not easy as space is very tight and there is a fan belt very close

[kevtherev]

I've had a wet gauge on the high pressure switch.
It was connected for a week.
It rarely dropped below 40 psi if ever

[itchyfeet]

Thanks for the info 2.75 bar in new money
I wonder if the high pressure switch pressure variation hot to cold is dependent on engine condition.

[wizwilson]

ok Kevtherev , could you put the oil gauge on the low pressure and do the same test, then we could see what the pressure difference is between the 2, this would gives a rough percentage loss.

[kevtherev]

The gauge was moved many years ago, I put it at the HP site in error.
It now lives in the lifter gallery, where oil pressures vary wildy depending on temp and rpm. as itchy says.
I like it here, it is more sensitive to the above influences.

I might add at the HP site hot oil did give lower idle speed pressure, but not as low as in the lifter gallery

[ScienceBoy]

Ah now, I've just bought the double gauge sender (continuous and alarm) and now Kev has me concerned! This type needs to go in HP location.

I was actually looking at this post to confirm where said location is. I read it's behind the exhaust shield as you look up past the engine mount. I assume that's the thin bit of sheet? Anyone have photos? I hear it's a bit tight?

[itchyfeet]

High pressure switch if you have one is just by the oil filter below water pump, you can just see the oil filter in this pic at the bottom

[ScienceBoy]

Ahhhhhhh. Nice one. Ta

[123-jn]

My pressure sender is in the HP site with a temp sender and it reads 80-90 PSI at cold tickover with 15/40 shell helix, as the engine warms up this falls to 30-40 PSI at tickover with the temp at 80-85 degrees. My oil cooler keeps the temp at this level unless I climb a nasty hill or drive at 70 plus on the motorway in which case the temp can rise to 90-95 degrees (cooler has a reasonable flow of fresh air but not as good as if it was at the front) . At this temperature if I come off the motorway and tickover at a junction the pressure is down to 20-25 PSI. At a constant 50mph even at this temperature I have 50-60 PSI. This has been checked against a wet gauge and my readings are good from 40 up to 90 but just a tad low under 40 so there you go. I have tried them in the gallery plug but they were not all that different except at tickover where they are about 10 PSI lower.
My engine was rebuilt 7000 miles ago and the crank was in spec for normal shells , the cam was new as was the oil pump which is a 30mm heavy duty. Before I had the oil cooler my van would run up to 110-130 degrees on a fast run or up a steep incline and at those temperature the oil pressure really dropped away worst was 10 PSI at tickover once thus the oil cooler was FITTED. These engines really do run their oil hot without a cooler.