Inverse relationship between oil pressure and engine revs?

[Guest Macnoz]

Inverse relationship between oil pressure and engine revs?

 

 

It doesn’t seem to make sense but my 40hr 2200 Jab engine displays instantly increasing oil pressure as I throttle back from say 3000 to 2900.

 

It approached the yellow band on gauge on full power about 10mins into climb on first flight of the day.

 

Easing back revs restored pressure to middle of the green.

 

 

Yes there is adequate oil in sump shell aero 100 after changing from mineral run in

 

 

Oil temp was in the mid 50’s on guage –not that I’ve ever believed how low this shows on any Jab that I’ve driven!

 

 

CHT and EGT normal

 

 

Attitude makes no difference.

 

 

Does not replicate on full power test on ground

 

 

No I wasn’t very high

 

 

Mr Jabiru spoke about cavitation until engine warm up – I don’t think so

 

 

Any ideas or similar experience

 

 

[facthunter]

Low pressure.

 

100W is pretty thick oil. At mid 50's temp I would not rule out reduction of flow on the supply side. You only have atmos. pressure less your altitude effect to push the oil thru. till it gets to the pump. Nev...

 

 

[Captain]

Macnoz

 

 

 

My 3300 does something similar although probably not to the extent that yours does.

 

 

 

Once the oil is warmish the pressure will rise as the revs rise until it drops off a little as it rises further, but it quickly stabilises and doesn't continue to drop.

 

 

 

I have always assumed that the drop was when the spring loaded pressure regulator/limiter opens, and mine then appears to sit at around 2.6 - 2.9 Kpa at cruise at 80C.

 

 

 

Is that similar to yours or is yours more extreme?

 

 

 

Regards

 

 

[Modest Pilot]

All the 3300 Jabs at our field do this; it’s cavitation on the supply side.

 

With 100W oil stops at around 70-75 deg oil temp. With 15-50W oil stops at around 10 deg lower oil temp.

 

If you are able to reduce power below 2700rpm after T/O it will also stop. Occasionally occurs at higher oil temp with hot oil at high power settings, reduction of rpm will fix and you can return to higher power without it reoccurring.

 

Opinions at the factory vary as to the cause; the most honest one is its air getting in the supply side; what else could it be!

 

I have been assured that it’s O K but I wonder what the effect of air getting into the hydraulic lifters is doing, I hear it damages Rotax 912’s, it’s the reason you can not turn that engine backwards on the ground.

 

Feedback from all you engineers out there please!

 

 

[Guest Nelson Smith]

Hi Mac,

 

Our Jab oil pressure was doing similar things till I replaced the oil pressure guage sender.

 

Nelson

 

 

[Guest Macnoz]

thank you all

 

L2 changed oil pressure relief valve and oil.

 

Just did 1.1hrs in it and it went to red line at one stage so I had two out landings to be sure to be sure (no Irish man ever says this but I thought I would humour you) Full pressure on run up and take off and and generally all over the place.

 

He is changing sender tomorrow on Jab advice.

 

will let you know how it goes

 

 

[Guest Macnoz]

Sender unit it was.

 

Got one down the road at the auto factors-- same number as the original and up up and away

 

 

[Captain]

That's been a useful discussion of an issue Macnoz.

 

 

 

Thanks for the post and for the feedback.