Oil Pressure.. or lack of it.

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itchyfeet
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

https://www.opieoils.co.uk/p-69400-fuch ... e-oil.aspx" onclick="window.open(this.href);return false;

15W 50

Not my idea thanks to Andrew at Campershack
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

Aidan wrote: I don't know if VW went to the 0.9 switch in production or not

Testing it is mentioned in the 1992 workshop manual (17-7) so I guess they fitted it in production
http://syncrosport.com/info/manual/VW_T ... hanics.pdf" onclick="window.open(this.href);return false;
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

bigbadbob76 wrote:
937carrera wrote:- Original spec was 20W50, I think, and that's what all the factory manuals will assume is in the engine when giving parameters.

I'm trying to find original spec for the oil used to take measurements, the section that specifies min 2 bar@2kRPM @80*C doesn't say and the owners manual suggests several different oil weights depending on ambient temperature range.
I always thought 15W40 was original spec but can't prove that's what was used when pressure testing. hmmm......


A very good point
The WBX 2.1 manual says VW 500 00 or 500 01 (17-7)
http://syncrosport.com/info/manual/VW_T ... nj_Ign.pdf" onclick="window.open(this.href);return false;

the owners manual says the same and advises agains single grade
http://www.westfaliat3.info/July_1990_V ... bookWM.pdf" onclick="window.open(this.href);return false;

anybody find a good definition of VW 50 000 or VW 50 001?
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937carrera
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

I think we have to take the owners manual as best guide.

Changes in oil specifications continue over time, but the multigrade nature can still vary and is a distinct parameter. eg, years ago you could by SE grade, then SF, then SG etc to what is current today. All the while you were able to get these oils in different grades.

It's often the case that a change in specification arises for environmental reasons, so one additive is replaced by another.

The oil pressure test seems to be based on the "B Improved lubricity" oil, dunno what that is, if you look at the A list, for us 20W50, 20W40, 15W40 and 15W50 all fit UK temperatures, depends what low temperature you are planning for. We are at the upper end of the range at the moment :)

I don't think VW pushed single grade over multigrade on that page 85 in the linked manual
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

I wonder if you are over thinking this
what matters is has your engine got enough pressure
who cares of you use a better oil to achieve better pressure.
VW test is still the benchmark but worth testing it stinking hot too
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Re: Oil Pressure.. or lack of it.

Post by bigbadbob76 »

itchyfeet wrote: anybody find a good definition of VW 50 000 or VW 50 001?

I had a look, couldn't find a spec but this 15W40 conforms.

http://www.platinuminternational.com/ex ... AEES43.pdf

and this refers...

Volkswagen Motor Oil Specifications-
VW 500.00
Volkswagen specification for multigrade engine oils for gasoline engines with SAE 5W-X/10W-X viscosity. This is an "old" oil specification and is applicable to engines built before model year 2000 (up to August 1999). Oils with an approval made post March 1997 were given an alternative, later VW specification.
VW 501.01
Conventional motor oils suitable for some VW engines built before MY 2000. This is an “old” oil specification and is applicable to engines built before model year 2000 (up to August 1999). Oils with an approval made post March 1997 were given an alternative, later VW specification.
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

https://www.opieoils.co.uk/c-745-vw-501 ... e-oil.aspx

The above page is the page for 501.01 oils which includes oils with grades including

10W30 to 10W60
15W30 to 15W60
20W50

So I don't think the spec has anything to do with viscosity.

I have been thinking about why do we measure oil pressure. I think we do it because pressure is easier to measure in an engine than flow. What is needed is a constant oil film on the bearings to allow almost friction free movement which is continuously replaced to reduce degradation due to heat and to actually carry the heat away. Oil pressure is therefore an analogue / substitute for flow. They are related in that if the oil pressure drops, then within a normal range flow reduces for a given temperature which leads to oil degradation and overheating.

Multigrade oils behave like a 20 single grade oil at say 0 degrees C and like a 50 single grade oil at 100 degrees C, the different range of viscosities generally being utilised to adapt to different ambient temperatures. Hotter day > hotter engine > higher viscosity required to achieve the same pressure or keep the flow down to the anticipated rate.

As I said before an oil pressure switch sees a less viscous oil as a hotter oil for a given temperature which for me really throws into question the value of a pressure specification when a multigrade meeting the stated VW specification can be anything from a 30 grade to a 60 grade :!: Compound that with the fact that there is no adjustment for oil grade on the various oil pressure warning systems on our engines.

Anyway that's my thought experiment for this evening, over to others to contemplate and contribute :D
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

So what oil do I put in my T25? :rofl
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Re: Oil Pressure.. or lack of it.

Post by bigbadbob76 »

937carrera wrote:I have been thinking about why do we measure oil pressure.

As you say, we need a film of oil between moving surfaces to reduce friction and therefore wear.
If the oil is too thin/not viscous enough to provide an adequate film then this will show as low oil pressure.
It's a simple way of measuring viscosity.
and of course... pressure, flow, viscosity and temperature are all inter-related.

It's also a measure of wear in the engine surfaces.
As clearances increase, pressure will drop due to higher flow.
Depending where in the engine you are measuring and where the wear is, this reduced pressure may mean that some areas furthest from the pump don't get enough oil resulting in increased wear.

So yes, I agree with what you say in a roundabout way, looking at the same end point from a different angle. :lol:
But I do think pressure is relevent as a wear indicator if you specify which oil viscosity you are using for the test.

Taking it further.... using more viscous oil will increase pressure but reduce flow... is this a bad thing? I think not in a worn engine with increased flow due to higher clearances.

aggghhhhh...... what have you started???? :lol:
Last edited by bigbadbob76 on 18 Jul 2018, 21:11, edited 4 times in total.
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937carrera
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

itchyfeet wrote:So what oil do I put in my T25? :rofl

I'm unsure if that was pure contemplation or a mere contribution :rofl
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

bigbadbob76 wrote:
Taking it further.... using more viscous oil will increase pressure but reduce flow... is this a bad thing? I think not in a worn engine with increased flow due to higher clearances.

I would go along with that

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

More viscous oil = lower flow, higher pressure.
Engine wear giving greater clearances = greater flow, lower pressure

as you said above, but approaching the question from the flow perspective might make it easier, but we cannot forget that the flow is there to take heat energy away.

bigbadbob76 wrote:
aggghhhhh...... what have you started???? :lol:

I know, but this isn't a typical oil thread, is it ? :lol:
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Re: Oil Pressure.. or lack of it.

Post by itchyfeet »

937carrera wrote: but we cannot forget that the flow is there to take heat energy away.

But is that true?
Isn't most of the heat generated in the combustion chambers and cooled by the water jacket?

Isn't the oil to lubricate and lower friction and reduce heat generation rather than remove it?

Doesn't oil get hot when you pressureise it so grearter pressure means more heat in the oil but that comes mechanically from the pumps energy and not necissarily throught heat generated in the moving parts.

This is all just my gleaned limited knoledge of course, happy to be educated better?
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

I naturally agree the oil lubrication reduces friction, which means a huge reduction in heat generation compared with the alternate metal to metal contact, but that doesn't mean that oil doesn't act as a heat transfer media, the same as coolant. Even more obviously the case when you consider vehicles with oil coolers. The heat being given up is coming from somewhere

I went on a quick google and found this http://wrap.warwick.ac.uk/3494/1/WRAP_T ... 1994_1.pdf, pages 46 and 82 discusses heat transfer within engine bearings while https://www.machinerylubrication.com/Re ... on-dangers is a broader discussion which includes the following

Finally, moving oil serves as a heat exchanger by displacing localized heat generated in load zones outward to the walls of the machine, oil reservoir or cooler. The amount of heat transfer is a function of the flow rate. Starvation impairs flow and heat transfer. This puts increasing thermal stress on the oil and the machine.

Pressure on the actual bearing surfaces is many times higher than what we read on our gauges, so there is heat generated in that process as you say, but of course when the oil leaves the bearing surface and returns to lower pressure that heat from compression is given up, the flow is what allows this to happen.

Thanks - I didn't think my investigation of my DOPS buzzer going off would get me into glancing through a Phd paper this morning :lol:
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Re: Oil Pressure.. or lack of it.

Post by bigbadbob76 »

937carrera wrote: Another thought.......... a pump produces flow, it is the restrictions to that flow that create the pressure.

In the interests of debate.. :wink: .... 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. :P
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Re: Oil Pressure.. or lack of it.

Post by 937carrera »

I'll go along with you on that too.

However, I am becoming firmer in my opinion that for our vans any talk of oil pressure specifications, with no clear statement of one of the key test parameters being the grade of oil, gives much more appearance of precision engineering than is really the case.
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
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