Sorry for delayed thanks. Thanks for your input.
So likely enough it is the sender.
My rotax guy in colombia concurs. He has been looking after and modifying
rotax for a long time and says he has never had an issue with the oil
system; it's always the sender. The other thing he suggested is that it
might be the filter.
So in conclusion change the oil sender and the oil and filter.
But so weird that the oil pressure should rise with altitude!
Thanks
Will
William Daniell
LONGPORT
+1 786 878 0246
On Sun, Jul 18, 2021 at 10:09 PM Bud Yerly <budyerly@msn.com> wrote:
> Duncan,
>
> Well said. The pressure pickup is in the area where the pump drives oil
> to the system first and measures the pressure after it oils the bearings.
> Then in a turbo the oil goes to the turbo and back to the suction side. Oil
> that spews off the bearings and moving parts collects in the crankcase and
> the exhaust blow by of the rings pressurizes the crankcase just enough to
> push the oil back to the tank. The tank is vented to neutral atmospheric
> pressure so as not to over pressurize the system.
>
>
> The issues with oil pressure sensing are interesting. Off the top of my
> head:
>
> 1. Oil pressure gauges are not absolute so they can vary with altitude.
> However, below 10,000 feet science says the change in atmospheric
> pressure with altitude is only 5 pounds from the surface to 10,000 feet.
> Barely readable on a resistive sensor driven gauge.
> 2. Crankcase pressure affects oil pressure. In a pressurized
> crankcase as in the Rotax, the added crankcase pressure will add to
> pressure (typically 3-5 PSI). See the Rotax installation manual.
> 3. Resistive sensors must ground properly. Those who use Teflon tape
> beware of your ground. The ground has to be perfect.
> 4. Oil pressure fluctuations coming from the oil pump are very large.
> Although
> the oil pump outlet goes around the oil galleys to the turbo pressure line
> and oil pressure sensor as Duncan said, that fluctuation in pressure is why
> there is a small orifice in the sender. It is to smooth out the
> pulses. Mounting the sender on a longish hose with a very small
> orifice, smooths oil pressure fluctuations. The Rotax is a tight
> engine and the pulses from the oil pump can still be seen on a direct
> reading gauge with no orifice dampening.
> 5. Gauges and sensors together are only as good as their calibration. Even
> your direct reading gauges are not terribly accurate. Calibration for
> me uses three gauges. Two mechanical and one electric. The two
> reading the same are normally right.
> 6. Resistive sensors and digital sensors vary in accuracy with
> pressure increases. 5% errors are not uncommon known as hysteresis or
> deviation from linear. Resistance gauges have a brass or aluminum
> diaphragm or pressure dome which fatigues over time due to changes in
> pressure as well as external vibration. As the pressure increases
> there is a resistor bridge that changes resistance with the stretch of the
> dome. There is even a temperature compensation resistor in the
> resistive bridge normally. So, at 70 PSI the oil pressure sender and
> gauge may be plus or minus 3.5 PSI which is perfectly normal and safe.
> 7. Rotax high oil pressure indications, once the engine is warm,
> mechanically, does not happen unless the oil pressure control spring/piston
> is stuck. By the time the oil goes around the system, the pressure is
> not going to be really high unless you see other issues. Changes in
> oil pressure and temperature tend to go hand and hand.
> 8. Oil pressure gauges are only as good as their calibration. For
> instance, the type wire and distance from the engine sensor changes
> the gauge reading very slightly. Corroded connectors create high
> resistance. Low or high voltage also changes the reading. In the
> Dynon, the engine monitor normally sends anywhere from 4.6-5 volts to the
> sender. The resistance drives down the voltage and the now milliamps
> going back to the instrument will vary with any wiring resistance.
>
>
> My experience with the Jab and Rotax has shown that over time, a high
> pressure resistive sensor will lose accuracy over time due to fatigue. I
> have two of our Rotax Europa clients here in Florida that fly indicating
> 40-45 PSI cold and drops to 30 in cruise. The Rotax gauge calibration
> showed actual / indicated is about 60/45, 40/35, 30/28, 10/0. The Jabiru
> I have in the shop right now showed 60/80, 50/75, 30/50, 10/0. Heck of a
> thing. Both are similar resistive senders from the same manufacturer.
> Changing
> the oil sender brought the Jab back to within 3% tolerance and one of the
> Rotax owners is back to where the plane was when new.
>
>
> If the engine oil temp is normal and the engine is running fine, test the
> pressure sensor. Running a direct reading oil pressure gauge is a pain. A
> leak in a direct oil pressure gauge is an interior disaster, it requires a
> new hole through the firewall, so make a pressure sensor tester and hook it
> to the aircraft and ground it. I really should take a picture of my dumb
> tester. Although I have a new VDO gauge and sender I use for testing,
> the air pressure regulator and a direct pressure indicator that read the
> same could be used rather than another electrical sender, but for me it is
> handy. See the drawing below.
>
>
> Time for bed,
>
> Bud Yerly
>
> [image: Diagram Description automatically generated]
>
>
> *From:* owner-europa-list-server@matronics.com <
> owner-europa-list-server@matronics.com> *On Behalf Of *D McFadyean
> *Sent:* Sunday, July 18, 2021 3:52 PM
> *To:* europa-list@matronics.com
> *Subject:* Re: Europa-List: Oil pressure rises with altitude
>
>
> <<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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