Oil Pressure.. or lack of it.

[bigbadbob76]

If it doesn't seize it's fine.
Probably a lot of truth in that, mine was running fine with less than 0.25 bar at hot idle, (the wee flashing light came on)
The engine failed on one or more catastrophic coolant leaks and the resulting overheating, it didn't seize due purely to low oil pressure.
Nothing to say it wouldn't have though, given time.

[silverbullet]

A typical fully rebuilt engine from me (new everything) will still only make 1.2-1.5 bar at idle when hot (fan cutting in/out) and that's with a standard 26mm pump.
It simply doesn't turn fast enough on these engines to move a sufficient volume of oil to make better pressure.
However, blip the throttle and the pressure will instantly jump to 3.5+ bar.
A flat four will quietly soldier on with almost no oil pressure untill one big end bearing is finally beaten out to nothing and then spins in the rod and starts to friction weld that to the crankshaft.
Shortly afterward it goes BANG and catastrophically ventilates the crankcase.

Sent from my S60 using Tapatalk

[silverbullet]

Another thought.......... a pump produces flow, it is the restrictions to that flow that create the pressure.

In the interests of debate.. .... does the pump produce flow? or does it produce a pressure differential across it's ports, which in turn causes flow?

As an Elex engineer I always equate pressure to volts (potential difference), flow to current, and restrictions to resistance.
You can't have current without a driving voltage, but you can have volts without current, same with oil pressure/flow.

Oil pumps move volume, the restriction to that flow is the bearing clearances. The result is back-pressure, regulated by the relief valve.

Sent from my S60 using Tapatalk

[bigbadbob76]

Anyway, how about a coolant pressure gauge so you know if your fire ring has gone and you're pressurising the cooling system.

[itchyfeet]

Anyway, how about a coolant pressure gauge so you know if your fire ring has gone and you're pressurising the cooling system.

A fire ring is what you get after a curry, we're not in USA its, a compression seal

[bigbadbob76]

fire ring is what you get after a curry.

It upsets your body's cooling system though doesn't it.

[itchyfeet]

fire ring is what you get after a curry.

It upsets your body's cooling system though doesn't it.

yes and you get gasses leaking
Just because Trump popped around your neck of the woods doesn't mean you have to get all 'merican on us.

[bigbadbob76]

I'll just say head gasket next time.
It must be the wife's influence, she's Texan.

[937carrera]

I've been doing some more reading around

This page confirms that specification and grade are independent, especially with the older specs

https://www.oilspecifications.org/artic ... lained.php

The Aussies have a 20W60 option https://www.penriteoil.com.au/products/classic-v-dub suitable for WBX

Richard Atwells pages are a very good source of information for T2 engines including the type 4 ones. In here he's clear that the SE spec was first introduced in 1971 and it was not until 1987 that there was an update to SF. Of course in the 1970's "everything" used 20W50. There is also a comment about oil temps being lower in a water cooled engine.

http://www.ratwell.com/technical/OilSelection.html

He also says this

All these oil recommendations from VW are fine except they forget to mention one important detail: they are the recommendations for a NEW engine. As the engine ages, the bearing clearances increase and you need to use a thicker oil to maintain proper oil pressure. What's good for your engine isn't necessarily good for someone else's engine simply because of the difference in mileage and actual wear.

One way to choose a grade of oil for your climate is to check the oil pressure using the Bentley specs as a benchmark. The engine requirements specify an optimal oil pressure for longevity. VW says that you should see 42 psi with SAE30 oil at 175F when the engine rpm is 2500 (Type 4 engine data).

If you have an oil temperature gauge, an oil pressure gauge and a tachometer you are closer to determining if your oil is providing adequate lubrication or to help you select another grade. If the reading drops below 28psi you could benefit from switching to a thicker oil.

Interesting, though not surprising that he refers to a min spec of 2 bar (well, a bit less than that) at 2500 rpm, same 2 bar spec for the WBX but at higher revs

I have yet to check the owners manual for my CU van but suspect it will be similar to the one Itchyfeet linked to in terms of having multiple mono and multigrades.

I have yet to see anything definitive, but the impression I get is that 15W40 was probably the oil originally used in WBX when introduced in the UK, replacing the 20W50 in the Aircooled engines. I'll try and go through my history files and see if there's any further information there but I doubt they go that far back for the T25's. My 412 does go back to first service invoice in 1975, but the VW dealers invoices just say engine oil, occasionally saying Castrol GTX

I think the conclusion on the oil pressure testing is that VW have not published the viscosity grade of oil to be used for the test, perhaps because they simply expect the grade of oil to be correctly matched to the ambient temperature. If your oil pressure is a little low on your well used engine, then moving to a more viscous grade to maintain pressure (and consequently flow rate) is the right thing to do.

So, 15W40 original moving to a 15W50, just what Andrew at Campershack already recommended to itchyfeet.

I'll await delivery of my new pressure tester then measure again before and after oil change.

[bigbadbob76]

Good plan. think I'll do the same at my next oil change.

[DoubleOSeven]

My 2 penneth. I might go 15W-50 in the summer and 15W-40 in the winter. My oil temp barely hit 100C despite this weather on a long drive back from Santa Pod yesterday. I have gone to a 80C thermostat though, which probably explains the oil temp. It used to be at 104C but I couldn’t go over 65mph without it rising and me worrying. Now I can do 80mph and it still stays under 110C.

2.1MV on Pierburg. No oil cooler or warmer. 15W-50 oil.

[itchyfeet]

Have you verified those temperatures with a thermocouple down the dipstick tube?
Where is your sender/sensor?

My 2 penneth. I might go 15W-50 in the summer and 15W-40 in the winter. My oil temp barely hit 100C despite this weather on a long drive back from Santa Pod yesterday. I have gone to a 80C thermostat though, which probably explains the oil temp. It used to be at 104C but I couldn’t go over 65mph without it rising and me worrying. Now I can do 80mph and it still stays under 110C.

2.1MV on Pierburg. No oil cooler or warmer.

[DoubleOSeven]

Same place as yours, remember.

[937carrera]

An interim update while the oil is draining and the engine cooling down.

I retested with my new 7 bar oil pressure gauge with the following results



Flat Cold
1000 rpm - 4.0 bar
2000 rpm - 4.3 bar
3000 rpm - 4.7 bar

Warm - coolant needle off the white section
1000 rpm - 1.7-1.8 bar, needle flickering
2000 rpm - 3.4 bar
3000 rpm - 4.0 bar

Hot, coolant needle just below LED, fan running, the hottest I have ever seen it when running normally, reasonable to assume oil was 80 plus degrees
1000 rpm - 0.9 bar
2000 rpm - 1.8 bar
3000 rpm - 2.5 bar

Those readings are better than I saw before, I am assuming the new gauge is more accurate as it has a narrower range

Sorry, no oil temps at this stage as I didn't have my thermocouple with me, but that has just arrived so I will put the new oil filter and 20W50 mineral oil in and retest

Still 1.8 bar at 2000 rpm is just low enough to trigger the DOPS system (see picture)

Nice new Mann oil filter going in, the one I removed was a Comline, never heard of them

[bigbadbob76]

I'd not worry about those pressures. It's within spec as far as you can tell. Stick in a black 1.4 bar switch and the 20w50 oil and enjoy. [THUMBS UP SIGN]


Sent from my iPhone using Tapatalk