Duncan thanks
Further trying the patience of the forum
So further investigation of test flight photos from 2017 indicates that the
engine has always done this to a limited extent, 55psi at 8500 (I did the
test program out of SKGY 8500msl) and 60-63psi at 11500' at same MAP.
>From what I read on the web these pressures are a little bit high - is this
correct?
What I am getting now is the 55 psi at sea level but close to 70psi at 7000.
- I have already changed the pressure sender - no change in the reading
- I have ordered a new spring and regulator mushroom.
- I will check hose clamps and the breather
- I will also check the torque of the turbo banjo fittings and the turbo
oil sump
- I will change oil and filter
Please correct me if I'm wrong but as I understand the oil system
1. The oil pump draws the oil from the tank via the oil radiator to the
pump.
2. The pump the drives the oil through the engine internal channels and
the oil ends up in the bottom of the engine whence it is pushed back to the
tank by crankcase pressure.
3. The oil tank is vented and this also acts as the crankcase breather
(is that correct? there is no dedicated crankcase breather?). The vent is
critical because if blocked it will prevent oil being drawn into the pump
via the oil radiator.
4. In the case of the 914 there a supply line to the turbo and a
scavenge line from the small oil tank below the turbo.
Questions:
- Is the pressure regulator spring on the pressure output of the pump?
- At what point is the oil filter?
- And pressure sender? I think someone said that the oil pressure
sender is the "last thing in the circuit". If I remember correctly than an
obstruction in the system would cusue low oil pressure preading.
As I understand it, the pressure sender measures the difference between oil
pressure and ambient air pressur and as a result, all engines show a slight
increase in oil pressure with altitude - but not even close to 10psi.
Therefore I need a cause which increases pressure within the crankcase with
altitude thus pressurizing the oil system or alternatively a cause which is
"fooling" the pressure sender.
William Daniell
LONGPORT
+1 786 878 0246
On Tue, Aug 17, 2021 at 6:26 AM D McFadyean <ami-mcfadyean@talktalk.net>
wrote:
> I would check the suction side of the oil system pipework for leaks. Even
> a slightly loose clamp I have found to be instrumental in erratic OP
> readings, as air is drawn in to the system.
>
> The ball-and-spring pressure relief valve is a design-disaster, but not
> much you can do about it, other than check that the spring is not badly
> worn.
>
>
> Duncan Mcf.
>
> On 08 August 2021 at 19:42 William Daniell <wdaniell.longport@gmail.com>
> wrote:
>
> Following on my post of about month ago. I changed the sender for a new
> vdo but sadly the result is the same. My oil pressure increases with
> altitude...50psi at 29"map at sea level, 55-57psi at 5000' 29"map.
>
> At low rpm the reading jumps around 45-55psi and then settles down once
> rpm is increased.
>
> All other temps etc are green and stable: cht, oil temp, egt. And the
> engine is apparently running fine..smooth and the isual amount of power.
>
> I cleaned out the oil tank about 20 hours ago and purged as required.
>
> The sensor is a new vdo and I have dynon skyview. 325 hours on the
> engine.
>
> Any bright ideas?
>
> The oil pressure ball/spring perhaps?
>
> Thanks
> Will
>
> William Daniell
> +1 786 878 0246
>
>
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