Oil Pressure.. or lack of it.

[937carrera]

More experimentation and data points today

This time I both measured the length of the thermocouple into the dipstick tube, and that it was wet when removed before starting the engine.

Same as routine before, except more measurements along the way and timings. I started off at 1000 rpm, then when temperature had levelled off increased revs to 2000

Cold - 23 degree oil
1000 rpm - 4.2 bar
2000 rpm - 4.5 bar
3000 rpm - 4.8 bar

Warm - coolant needle off the white section, 60 degree oil (same coolant position 5 degrees warmer on the oil measured temperature)
1000 rpm - 2.0 bar
2000 rpm - 4.0 bar
3000 rpm - 4.2 bar

Hot, oil measured at 80 degrees (view this as a new measurement point, coolant just below LED, fan not on high speed)
1000 rpm - 1.2 bar
2000 rpm - 2.2 bar
3000 rpm - 3.2 bar

Hot, coolant needle just below LED, fan running, oil at 87 degrees which is as warm as it would go with stationary vehicle, measured oil temp 7 degrees higher
1000 rpm - 0.8 bar
2000 rpm - 1.8 bar
3000 rpm - 2.8 bar

I also noted the oil temperature at 1000 rpm as temperatures increased:

23 deg C - just nice for me, start
30 deg C - 3.9 bar - 2 mins
35 deg C - 3.7 bar - 4 mins
40 deg C - 3.6 bar - 6 mins
45 deg C - 2.8 bar - 8 mins
50 deg C - 2.5 bar - 9 mins
55 deg C - 2.3 bar - 10 mins
60 deg C - 2.0 bar - 11 mins
65 deg C - 1.8 bar - 12 mins
70 deg C - 1.6 bar - 14 mins
75 deg C - 1.3 bar - 18 mins
78 deg C - 1.1 bar - 26 mins, this was the maximum temperature achieved at 1000 rpm
85 deg C - 1.0 bar ---------------at 1000 rpm, at 2000 rpm this was 1.9 bar
87 deg C - 0.8 bar - 36 mins

I am getting the same pressure readings on coolant temperatures, with higher oil temperatures so the previous readings were not getting true oil temperature, my pressures are better than before.

The engine is actually meeting the 2 bar at 80 degrees C at 2000 rpm VW oil pressure specificatiion, at least on 20W50 oil, which is a valid altenative

For my engine it looks as though the DOPS system will be activating corrently when the engine oil is around 85 degrees or higher, a white DOPS switch and revs just above the 2000 rpm trigger level

I now have a black / 1.4 bar "high" pressure switch. Hopefully the engine will have cooled down while I have been typing this and if I get it changed I will take measurements again but from the low oil pressure switch location

The sweepstake is officially closed due to lack of entries

[937carrera]

Tests repeated, it was a little harder to take measurements this time as the pressure gauge was under the bumper, (readings from DOPS point in red where different)

Warm - coolant needle off the white section, 60 degree oil (same coolant position 5 degrees warmer on the oil measured temperature)
1000 rpm - 2.0 bar
2000 rpm - 3.2 bar - 4.0 bar
3000 rpm - 4.2 bar

Hot, oil measured at 80 degrees (view this as a new measurement point, coolant just below LED, fan not on high speed)
1000 rpm - 1.2 bar
2000 rpm - 2.5 bar- 2.2 bar
3000 rpm - 3.5 bar- 3.2 bar

Hot, coolant needle just below LED, fan running, oil at 90 degrees - 87 degrees which is as warm as it would go with stationary vehicle
1000 rpm - 1.1 bar - 1.1 bar
2000 rpm - 2.1 bar - 1.8 bar
3000 rpm - 3.1 bar - 2.8 bar

I also noted the oil temperature at 1000 rpm as temperatures increased:

50 deg C - 3.1 bar - 2.5 bar
55 deg C - 2.4 bar - 2.3 bar
60 deg C - 2.0 bar
65 deg C - 1.9 bar - 1.8 bar
70 deg C - 1.6 bar
75 deg C - 1.5 bar - 1.3 bar
85 deg C - 1.1 bar - 1.0 bar
90 deg C - 1.1 bar - 0.8 bar measured at 87

Unfortunately the temperature probe came out while I was moving the pressure gauge so it may not have been in exactly the same place so the tests may not be directly comparable.

For me the take away is the the pressure at the low pressure switch location is pretty much the same as at the DOPS point. I was expecting it to be a little bit lower due to pressure drop along the line, but the comment from silverbullet about back pressure suggested to me that it may not be lower at all.

I am really struggling with the engineering side of my mind to understand how the pressure at the low switch side is higher than at the high switch side. I could imagine that measuring errors due to the location of the temperature probe could mean that it is a false comparison, and also the engine speed for each test point, but for the final test the coolant temperature was pretty much the same as the previous test with the high speed fan operating.

Sticking a K-probe in the dipstick does get an oil temperature, but based on my experience I think there's easily 5 degrees C variation in measured temperatures simply from the insertion of the probe, without designing a more robust / reproducible insertion method.

Time for me to put the van back into camper mode. As always I'm interested in any opinions or experience of what the numbers indicate. I did notice that what was a sweet running van at engine start turned a bit knocky / rattly as the engine temperatures increased, aluminium case expanding more than steel components, not specific to any particular cylinder. Anybody else hear the same when testing, maybe it'll seem fine when the engine cover is back on ?

[itchyfeet]

I saw variation which I didn't expect so measure and measure again is the only way.

What I found was if you put a brick on the accelerator and held a steady revs and waited for the temp to rise and pressure to fall you got a higher pressure reading than if you drove it or revved it before getting up to temperature.

I could take a reading at 80 degrees 2000 rpm, blip the throttle and return it to 2000rpm and the pressure had dropped, so more going on that you think.

what matters is conststancy in method of measuring.

[itchyfeet]

I once met a bloke who did viscocity testing of oils, he was bonkers but knew a thing or two about the subject, he party trick was a sample of oil that he conditioned to be almost solid, tapped it on the table and it turned to liquid.
I suspect that the viscocity of the oil is not linear with temperature, pressure must play a part.

[937carrera]

OK, so you saw some variability too, as I thought the testing procedure (or at least mine) isn't robust enough for precision, but it still produces some sensible results.

I eliminated the throttle issue by tweaking the idle screw, which meant the engine ticked over + / - 30 rpm, but I also saw that when the fan came on the engine lost about 70 rpm with consequent change in oil pressure. I think that changes in engine revs also affect flow rate through the bearings which can cause an additional cooling effect. For the final test I switched the probe into 0.1 degree accuracy and you could clearly see the temps cycle up and down by a degree or so while on an upward trend.

I've seen a similar solid / liquid trick too, Royal Institution Christmas Lectures on TV probably, many years ago. Non Newtonian liquids, go make one http://www.bbc.co.uk/science/0/22880407

[937carrera]

It's been a while since we had a picture, I was quite pleased with the underside of the case when I took the cover off so I took a photo. Looks like a bit of CV splatter

The cover has been cleaned and all that built up grime & gunge has been removed so it will cool better

[tobydog]

I once met a bloke who did viscocity testing of oils, he was bonkers but knew a thing or two about the subject, he party trick was a sample of oil that he conditioned to be almost solid, tapped it on the table and it turned to liquid.
I suspect that the viscocity of the oil is not linear with temperature, pressure must play a part.

Non Newtonian flow, not sure if it's relevant to the above, but, relevant to injection moulding -

http://www.beaumontinc.com/injection-mo ... r-heating/" onclick="window.open(this.href);return false;

PS
Shear heat

[ajsimmo]

My 2 penneth. I might go 15W-50 in the summer and 15W-40 in the winter.

They have the same cold viscosity, so why change? Surely just let the "wideband" multigrade do its thing?
According to VW lubrication chart, 15W50 is good down to -15deg ambient, but only up to 30deg, so if anything you need a thicker oil this summer! (Weirdly it doesn't give a multigrade for above 30deg, just a straight SAE40).

[kevtherev]

I use 20/50 during the summer.
Touring hot countries.
At home it's changed to 15/40

[itchyfeet]

I use 20/50 during the summer.
Touring hot countries.
At home it's changed to 15/40

As Andrew says 15-50 does the same job for winter and summer and unless you buy cheap supermarket oil is not really any more expensive it helps with cold lubrication.
Even if you change twice a year and use cheaper 15W40 in summer it's worth using 15W50 in winter as 20W50 is seldom much cheaper.

https://www.ebay.co.uk/itm/Fuchs-Titan- ... xyEoFSZQIG" onclick="window.open(this.href);return false;

[kevtherev]

I use 20/50 during the summer.
Touring hot countries.
At home it's changed to 15/40

As Andrew says 15-50 does the same job for winter and summer and unless you buy cheap supermarket oil is not really any more expensive it helps with cold lubrication.
Even if you change twice a year and use cheaper 15W40 in summer it's worth using 15W50 in winter as 20W50 is seldom much cheaper.

https://www.ebay.co.uk/itm/Fuchs-Titan- ... xyEoFSZQIG" onclick="window.open(this.href);return false;

Yes I undetstand that.
The thing is when using 15w/40 I get an annoying oil light flash after a high speed run and then slow traffic in +30 deg heat.
The gauge tells me everything is fine and I have 14psi
Does not happen with 20w/50, gauge reads 18psi
Fit a new switch I hear you say, well I like to change the 'summer oil' so there.

[itchyfeet]

I use 20/50 during the summer.
Touring hot countries.
At home it's changed to 15/40

As Andrew says 15-50 does the same job for winter and summer and unless you buy cheap supermarket oil is not really any more expensive it helps with cold lubrication.
Even if you change twice a year and use cheaper 15W40 in summer it's worth using 15W50 in winter as 20W50 is seldom much cheaper.

https://www.ebay.co.uk/itm/Fuchs-Titan- ... xyEoFSZQIG" onclick="window.open(this.href);return false;

Yes I undetstand that.
The thing is when using 15w/40 I get an annoying oil light flash after a high speed run and then slow traffic in +30 deg heat.
The gauge tells me everything is fine and I have 14psi
Does not happen with 20w/50, gauge reads 18psi
Fit a new switch I hear you say, well I like to change the 'summer oil' so there.

15w50 will be rid of te oil ligt just as 20W50 will it's the 50 bit thats important but the 15 bit helps reducewear cold better then the 20 bit.

[kevtherev]

Yes I agree 15w if cold ambient was 0 deg
Here its 24 deg
Anyhow I think it's splitting hairs.
After 14 years I haven't had any mains thumping ...yet