<<If it were an obstruction the pressure would be high independent of
altitude....>>
An obstruction in an oilway would tend to result in a lower pressure, because
the
point at which pressure is measured in the Rotax is at 'the end of the line'
after all feed for bearings etc has been taken; it's what's left over.
I've spent the last year chasing odd oil pressures. What I do know is that the
oil pump (4-lobe, now 6-lobe in the iS engine) and pressure regulation (a ball
and a spring!, but a proper piston in the iS engine) leaves much to be desired
(e.g. behaves in odd ways if there is air in the oil, which is almost a
certainty
with the Rotax scavenge system). The later 912 pattern of relief valve
'mushroom'
confers little or no benefit from my experience, except the later plug
screw better supports the relief spring from buckling sideways.
What an electrical gauge shows (with inherent or built-in damping) is quit
different
to what a mechanical gauge shows in terms of the dynamics.
Possibly the deairing function of the scavenge system works better at lower
atmospheric
pressures and/or less air gets entrained in the oil at greater altitude?
Duncan McF.
> On 18 July 2021 at 19:38 William Daniell <wdaniell.longport@gmail.com> wrote:
>
> So today for the first time in a long time I climb to 5500 and to my
> surprise
I see my oil pressure at 67psi and on occasions rising to 72 psi, the top
of the normal range. Previously my oil pressure has remained around 55 psi.
>
> So I turn around and go home thinking that there must be an obstruction
> somewhere.
>
> So I get down to 3000 and the pressure goes down 61 and then to 2500 and
the pressure goes down to 56 - all straight and level and same rpm and manifold
>
> I land and the pressure is 54-55 which is normal at sea level. I take off
again WOT and steady at 55 and then the same thing happens as I climb.
>
> All other temperatures are normal at all altitudes. I have Dynon Skyview
and EMS.
>
> Take off oil temp at WOT was 60C so you would expect higher pressure which
didnt happen and at 5500 oil temp was 80C. Other oil temps were in between.
>
> If it were an obstruction the pressure would be high independent of
> altitude.
>
> Could it be a defective pressure sender? The oil pressure sender must
> measure
the pressure of the oil against something - presumably against atmospheric
pressure. If it is compared to atmospheric pressure then it must be compensated
in some for changes in pressure with altitude.
>
> Any thoughts?
>
> Will
>
>
> William Daniell
> LONGPORT
> +1 786 878 0246
>
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