Light Aircraft Association

Hi All,

Have just got a Luton Minor oil pressure is ok at start up 45-50 psi but drops to about 20 at 2900rpm sabilized around this for a while, but dropped down slowly to 12psi as it warmed up today forcing an early retreat. Temp seems ok.

Any ideas? delivery pilot did over fill it with avaition oil could that have done it?

Regards

Chris

You should never use aviation oil in a VW. Limbach explicitly say "under no circumstances".

I don't know if that is the cause of your problem, but I suggest draining and flushing all the oil and re-filling with the correct grade of automotive oil.

Then check the engine on the ground to see if it has improved. If that helps then it would probably be advisable to repeat the draining and re-filling to get rid of any traces of aviation oil.

If you had put w100 or S100 especially it would be too viscous.

Also, I have no authority on this matter, so gather your facts and discuss the way forward with your inspector and/or LAA engineering.

Hi Chris,
I've heard it debated before about using aircraft grade oil in VWs . Mark is certainly right about changing to automotive oils , I use 15/40 multigrade in my 1834VW . I don't think it will harm the engine using aviation grade oils and Limbachs remark about 'under no circumstances' is probably to appease lawyers , rather than being based on any engineering logic .
When you say that your oil pressure drops to 12psi, is that at idle or at 3,000rpm ? I know that on mine just prior to shutdown after a flight it idles with oil px at around 15psi, and at cruise rpm it stays at about 45/50psi .
The most likely culprit would be the oil pressure relief valve spring, which could be getting a little tired. I fitted an uprated one to my VW when I rebuilt it ,available from bug tuning shops.
Keep the Luton flying mate, I love 'em .

Sound like a pressure relief valve not seating, I know nothing about VW but I am sure there is one.

Not knowing much about AV oils, if they are synthetic or have synthetic properties, i would like has previously been posted dump the oil and refill with a HD 30 oil as would be used in the car. Bug engines dont like multigrades up em. It would also not go amiss to replace the spring with a HD version as also posted. Sometimes they stick (at least on the road) causing the oil pressure to drop.

normal oil pressure is 1.5 bar @2000 RPM, with the oil at 80°c But according to VW themselves, is that if you have 1.5bar of pressure when the oil is 80 degrees Celsius, and at 2000 RPM then you don't have a oil pressure issue.

Someone once told me that one should have at least 10 psi per thousand revs. For what it's worth, my recently rebuilt (crank grind, new bearings and oil pump) 1834 runs at 50 psi @ 3,000 rpm on 20/50 oil with no oil cooler.

The Great Plains VW engine assembly manual suggests:
Minimum oil pressure at cruise 28 psi @ 2,500 rpm
Maximum oil pressure at cruise 70 psi
Average oil pressure at cruise 40 psi
Maximum oil pressure cold 90 psi.
And for oil - straight 30W (automotive detergent oil) in the summer and 10W30 in the winter.

If you have another oil pressure gauge handy, it might be worth your double checking the low reading. I say this because I saw my oil temperature over several flights gradually starting to climb and I panicked. I tried a variety of different oils and additives, all to no avail, eventually only to find that the spring inside the gauge was slowly giving up the ghost and allowing the gauge to over-read. I realised what was happening when I hauled the aircraft out of the hangar one day to discover that the oil was already at 60 degrees C. Gauges do very occasionally tell lies!

Good luck solving the problem.

Thanks all will change oil this weekend... check releif valve and see what happens!

Chris Burton

Gauges do very occasionally tell lies!

...and so do the sender units!

For what its worth, rebuilt 2ltr VW 60lbs without cooler, 25 with then replaced pipework and got it back up to an acceptable 40-45lbs
M