Oil Pressure.. or lack of it.

[itchyfeet]

Same place as yours, remember.

no sorry I dont remember
mine is in the oil filler tube location now
it was in the oil pressure relief valve but it was in accurate there.

[937carrera]

PLESE SEE LATER POST FOR BETTER MEASUREMENTS

Oil change and new filter fitted, some interesting conclusions. (Lexicon 20W50 no name no spec mineral, not the sort of stuff I would usually recommend, but at least I know what it is and it's cheap for testing, Mann filter)



Cold - 43 degree oil
1000 rpm - 3.4 bar
2000 rpm - 4.1 bar
3000 rpm - 4.4 bar - a bit lower than before, but the engine was certainly warm from residual heat

Warm - coolant needle off the white section, 55 degree oil
1000 rpm - 2.2 bar, needle no longer flickering
2000 rpm - 3.9 bar
3000 rpm - 4.1 bar - better than before, pressure more stable, perhaps benefitting from the new / better quality filter

Hot, coolant needle just below LED, fan running, the hottest I have ever seen it when running normally, oil at 80 degrees (photo taken a little earlier)
1000 rpm - 0.9 bar
2000 rpm - 1.8 bar
3000 rpm - 2.9 bar - a little higher pressure at the higher end

You can see that the oil temperature for this test in the photograph was 76.9 degrees. I really struggled to get it up to 80 degrees. What I was doing was allow the engine to idle at 1000 rpm, the oil temperature peaked at 65 degrees. Next stage was to increase the idle to 2000 rpm. This allowed the oil to achieve 75 degrees and then it started to cycle up and down a couple of degrees. At this point the fan was switching on and off its highest speed. I then moved the revs to 3000 rpm and after an increase the temperature started to fall again. The "hottest" running regime was around 2500 rpm and by holding the engine at that speed I managed to get up to 80.

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

50 deg C - 2.4 bar
55 deg C - 2.2 bar
60 deg C - 1.7 bar
65 deg C - 1.4 bar
70 deg C - 1.1 bar
80 deg C - 0.9 bar

Conclusions - for now
I suspect the engine was already on 20W50 oil, the pressures were slightly better accepting that the readings were being taken about 5 degrees higher than before.
The coolant system is operating well, on the road it never gets as high as the LED needle so I suspect I have an 80 degree thermostat fitted
As revs go beyond 2500 rpm the additional oil flow through the bearings caused by faster oil pump rotation actually cools the engine rather than allows the additional heat being generated to increase the oil temperature
Engine revs dropped by about 70 rpm when the cooling fan kicked onto the high setting
The oil pressure at 80 degrees / 2000 rpm is a little below VW spec, but not catastropically

Next course of action is to get a black / 1.4 bar "high" pressure switch, fit than and take measurements again but from the low oil pressure switch location

Perhaps a sweepstake should be set up to predict what the oil pressure will be at that location

[itchyfeet]

Next course of action is to get a black / 1.4 bar "high" pressure switch, fit than and take measurements again but from the low oil pressure switch location

Seems like a waste of time to me as thats not where VW say to.measure it

I suppose you wil get some indication of pressure loss down the gallery but how does that help?

[937carrera]

Hmm, I thought that was where you were supposed to take the oil pressure readings from, haven't you got an flexible extension in place that allows easy connection of the low switch or oil pressure gauge, or have I misunderstood and you are taking readings from the high pressure switch location, or even somewhere else ? I haven't gone back over your posts to check.

If I'm already doing it in the correct method then even better, less work to do.

What I am certain about is that the high pressure switch location is the right place to take measurements for the DOPS system

Did you see the same thing as me on the oil temps plateauxing out at different revs and the peak for energy into the oil being around 2500 rpm. That quite surprised me.

[itchyfeet]

I meant what you have just done was a waste of time
yes low pressure switch nearly at end of galley is the point you should measure as it will be worst case.

[bigbadbob76]

It'll be interesting to compare pressures at the two pressure switch locations though.
I would expect the pressure at the "low pressure switch" location to be lower, as it's in the gallery rather than straight off the pump/filter.
Doesn't sound so good if you're only getting 1.8 bar at the filter at 2k at 80*C with 20/50 and an 80*C thermostat, I assumed you were measuring at the gallery.

[937carrera]

I don't think it was a waste of time for me. The DOPS system was triggering, and that measures pressure at the high sensor, so that has to be the right place to check for correct operation of the DOPS system.

I had already taken measurements, with an unknown oil, that had done 3000 miles, and as it turns out not a decent oil filter. On the engineering basis of changing one variable at a time I wanted to see what the effect of changing the oil was before I started taking measurements from the other location.

I have confirmed that the DOPS switch (white, 1.6-2.0 bar trigger one of the permitted versions) is working correctly and that if I want to reconnect the DOPS system I can either use the alternate permitted grey 0.9 bar switch, or go for the completely wrong black 1.4 bar one which will give me additional warning if the engine wears to the point where it drops to that level.

Changing the oil / filter also caused the oil pressure readings to become more stable and I found out how the oil temperature reacted to different engine speeds, which was not as I was expecting.

Hopefully these extra data points may be of help to others, I'll try and complete my set in the course of the next week.

Still waiting for entries into the sweepstake

[937carrera]

I am genuinely interested in how the oil temperatures increased for you guys, as I said I really struggled to get heat into the oil, did you ?

[bigbadbob76]

Mine came up to 80C within about 10 mins at idle and was still heading steadily upwards.
I used the works thermocouple so can't repaet it at home unfortunately.

[937carrera]

Interesting, mine wouldn't have gone beyond 65 on idle and it took 20-25 minutes to get to the point where the high speed fan activated including moving it to a 2000 rpm tickover.

It's going to kill my mpg calculations

[bigbadbob76]

I had to push and pull the thermocouple to find the highest reading. I don't think the oil is very deep when the engine is running so the thermocouple can poke out and read low.


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[itchyfeet]

no problem getting it up to 80 especially in this weather but it does take 10 to 20 mins never timed it but about that
100 takes a bit longer same when you drive it.
I use 1500 to 2000 rpm to do it with brick on accelerator
have you got an 80 degree stat in?
have you checked the thermocouple?

Hard to say how the other switch location will vary in pressure reading it depends upon if you have flow ( leaks) at the pump or the bearings, the former won't affect the readings as much as the latter.

[937carrera]

Thanks for that. I'm in two minds as to whether the thermocouple was properly inserted.

On the one hand when I inserted it the engine had just been started with the fresh oil and I watched the temperature as I slipped it down the dipstick tube. I moved it to the point where the temperature was already elevated, ambient was 24 and it started reading at about 43. So that made me think I was already in the sump, but the low peak temperatures is making me think it wasn't fully in the oil. Even so we all know that bought senders suffer from conducted heat / thermal log.

I'm on a Weber carb so it's easiest to simply move the throttle stop to increase the idle. I used idle initially, then moved to 1500, then 2000 to get more heat, finally moving it by hand to achieve the highest temperature of 80

I don't know what stat I'm running. What I do know is that once I got the coolant levels correct the water temperature has never gone beyond the LED. The first time the fan came on high speed it was that loud I initially thought a wheel bearing had suddenly failed, took me a couple of seconds to realise where the din was coming from. I'm not intending to take a look, if it aint broke don't fix it.

I'm happy that the thermocouple is working correctly. I used to use it for measuring intake temperatures on a turbo car and last time it was used it worked as expected. If you look closely you will see there are two K probes which means I can do a differential temperatures, in that setting both probes were measuring the same temperature yesterday.

I suspect I'm going to repeat the latest test, or at least part of it. If the probe wasn't fully inserted then my pressures will be better than indicated above

Can you remember what oil temperature you had when the high speed fan cut in ?

[937carrera]

I have particularly remembered this earlier post

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

I'm no expert on fluid dynamics, what I do understand, no lets call that appreciate, is that if the diameter of a tube is increased pressure will drop for the same flow, that's what happens with our crank bearings.

Instinctively I am expecting pressure at the low oil pressure switch to be lower than at the pump exit, but perhaps the effect will be less than might be anticipated, depending on where the back pressure is being created

[bigbadbob76]

You mentioned your fan was on at 80C oil temp. Mine wasn't. I dunno what you can read into that.
Sounds to me like your true oil temp was higher than 80 if the coolant was hot enough to put the fan on.
Just my 2p worth.


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