Oil Pressure.. or lack of it.

[937carrera]

Regular visitors may remember I did a post about installing a rev counter and along the way discovering that my tacho cable was cut. I joined it, finished the revcounter and went back to recommission the DOPS system which seemed to work perfectly. Well, that was winter and last weekend was the first time I used the T25 this year. About 10 miles into the journey the DOPS system activated. As I did 800 miles last year in blissful ignorance with DOPS non functioning I earthed the cable and continued the journey, resolving to check the oil pressure when back home.

So, today I got my pressure tester out and took some readings, it's not looking promising. My gauge isn't the best for oil pressure, accurance is probably no better than 0.2 bar, but better than nothing. I couldn't take oil temp directly as I didn't have my thermocouple with me. Pressure readings taken from the "high" oil pressure switch location. I also dug out my old Gunson tester to measure rpm as it was more convenient / accurate than the one in the dash which seems to overread by 50 - 100 rpm



Cold - engine stood for an hour
1000 rpm - 2.5 bar
2000 rpm - 3.0 bar
3000 rpm - 4.0 bar

Warm - coolant needle off the white section
1000 rpm - 1.5 bar
2000 rpm - 3.0 bar
3000 rpm - 3.5 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 - 0.7 bar
2000 rpm - 1.5 bar
3000 rpm - 2.2 bar
3300 rpm - 2.5 bar, this was maximum, higher revs gave no higher pressure

Pretty much confirms that my DOPS system is working correctly, and it's a real warning.

The engine in the van is a replacement DF with DG heads and inlet. I have the invoice from the installer and the description is for a "reconditioned" engine with running in procedures from The Engine Shop in Erith. It was installed in 2005 and has done 43,000 miles

The oil is in good condition, though to be honest I probably should do an oil & filter change so I know what grade is in it and redo the tests.

Any thoughts ?

I'm in the middle of checking a DG engine I bought a few weeks ago, so will probably rebuild that and swap the ancillaries over. My van's a late van, I assume with a late cooling system, but the replacement DG is an early case with a different water pump.

I could just try swapping over the oil pump as the one on the bench seems good

Are there likely to be any issues swapping the ancillaries over. Sadly I doubt the exhaust system will survive, anyway, here's a picture of the thermostat housing and engine bay so the eagle eyed can highlight any issues I am likely to encounter

Thermostat


Water pump and offtake for the oil pressure gauge

[itchyfeet]

Yes everything swaps over, except crusty exhausts, early and late water pumps both fit either engine, they are totally interchangeable except...

early case has no high pressure switch , best to fit an oil pressure gauge and ground the wire.
early exhaust has a few bolts in stead of studs in the heads.

Oil pressure readings should be at low pressure switch location so will will be worse.

[itchyfeet]

1.5 bar at 2000 hot should not trigger the buzzer, switch is 0.9 bar

I'd check the pressure with another gauge

[937carrera]

1.5 bar at 2000 hot should not trigger the buzzer, switch is 0.9 bar

I'd check the pressure with another gauge

Good point, I was focussed on 2 bar at 2000 rpm being minimum spec, the DOPS is lower than that

[937carrera]

Maybe also need to check the switch I fitted, I thought I had selected the correct one, maybe not ?

States 1.6-2.0 bar, so it would be operating if oil pressure was 1.5 bar at 2000 rpm

Just snapped this and uploading it before I put the carb back on - another story

[itchyfeet]

looks wrong to me 0.9 bar is grey

[937carrera]

I've had a look at ETKA and BW https://www.brickwerks.co.uk/brickwerks ... -switches/

According to BW It seems that petrol WBX had white for 85-87 and then for 88 on went to grey with an option for white. My version of ETKA isn't so clear on the early years, but does show both options for 88 on.

So, I either replaced like with like (there was a small oil leak), or when I went to the shop I was given a choice and went for the higher value meaning I would know about a problem earlier.

Now I know about an upcoming problem, I'll buy a grey one tomorrow and reconnect the DOPS system so it can serve it's function

I agree that the 2 bar at 2000 rpm minimum spec is tested at the low oil pressure switch so I might see if I can source another gauge and do that afterwards, at least doing it this way I have confirmed that the DOPS system / switch were working correctly. Some alternative data points too.

[bigbadbob76]

Your pressures don't seem too bad to me, a wee bit lower than you would like but I wouldn't panic about it.
IIRC the fan comes on at 87*C radiator temp, oil temp will be a lot higher at that rad temperature.
Sounds like your DOPS is working correctly but needs the grey switch to stop you panicing.

[itchyfeet]

Pressure readings taken from the "high" oil pressure switch location. ]

Oil pressure readings should be at low pressure switch location so will will be worse.

Check it again in the right place and with a thermocouple, anything else is not going to give you a good enough comparison to the spec beuse temperature makes a huge difference ( as you can see from my pics) and if you have slightly low pressure it's becuse you have leaks, leaks mean flow and flow means the pressure drops off further from the pump.

I'd also get a 0-10bar gauge higher range gauges are less accurate
https://www.ebay.co.uk/itm/Engine-Oil-P ... SwY3tbMfEw" onclick="window.open(this.href);return false;
https://www.ebay.co.uk/itm/12pc-ENGINE- ... Swm9tZ1hP1" onclick="window.open(this.href);return false;

P1100268 15W50 80 by Paul_Barr, on Flickr

P1100270 15W50 100 by Paul_Barr, on Flickr

[Aidan]

in a perfect world a wbx should make 2.0 bar hence originally fitted with 1.8bar white sender but VW obviously found that as they got tired they didn't always make that so went to putting the 0.9 grey in on the basis that the bod wouldn't go off and the vehicle wouldn't keep coming back and hey it was an old van and once out of warranty who cares if the engine goes bang
You could compromise and fit the higher diesel one black 1.4bar
if you bought a new engine from VW it didn't come with a sender fitted
I don't know if VW went to the 0.9 switch in production or not, but interesting that pre 1988 the 0.9 switch is listed but with no application but after that it was listed as an alternative for both diesel and petrol engines
be interesting to see what result you get with new oil and filter as if you have a gauge fitted you get to know when the oil needs changing as you will observe the slight drop off in oil p at around 3000miles as the oil degradation starts to become apparent
as long as the pressure ramps up quickly with revs then these figures look fine I'd say

[937carrera]

Thanks Paul - I already ordered a 7 bar gauge from ebay this morning, much better granularity. When it arrives I'll also take my thermocouple with me to get the oil temps, but will probably take pressures at the same coolant gauge points for comparison, and note the corresponding oil temps.

Aidan, thanks for the reassurance, I think you are spot on about the reason for the spec change. Maybe I'll wait until the new pressure gauge turns up and redo all the measurements again, probably with fresh 20W50. Black 1.4 is definitely an option

[bigbadbob76]

I have a spare 1.4 bar black switch kicking about if you want it David.
I'm going the same way when I get the wiring in for it.

[Ian Hulley]

probably with fresh 20W50.

Fresh Mineral 15/40w and a new filter will give you the accurate readings you need ... 20/50w is the bury your head in the sand approach as you miss your initial warning when the buzzer goes off on the thinner 15/40.

Ian

[937carrera]

That's probably going to trigger a debate the Ian, which is fine, good to get other opinions, here's my thought process.

- I don't know what's in there, so I'll assume it's used, even though the colour looks quite good - "full service" done 3000 miles ago as I looked at the history file
- 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 still using 20W50 in my other type 4 engined car
- The move to thinner grades is for economy (internal drag reduction) and the tighter clearances in modern engines, augmented by moves to synthetic.
- If I put a W40 in there the oil pressure is going to be lower than spec simply because the thinner oil looks like hotter oil to a pressure gauge
- I don't know yet how long this new oil will be in the engine, so no point using expensive stuff
- Any modern oil is going to be technically better than what was made 30 years ago
- I know itchyfeet moved to a W50 oil as part of his oil pressure investigation work and saw an improvement in pressure

Given free reign I would probably choose to put in Millers CFS 15W60, but their Classic Sport 20W50 is probably more than adequate.

Of course I could be wrong on any of the above points

[bigbadbob76]

- 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......