REFLECTOR: Fuel Pressure Reads zero or low/intermittent -- SOLVED

[Donald Royer]

If you have your oil temperature probe where I think that you have it, your
are NOT measuring the oil temperature at all. I think that you are simply
measuring the temperature or the engine block. The space behind the plug
furthest from the prop.(the "stronger" spring) will contain oil only then
the main oil bypass value is open.

I have examined this plate off of the engine, and I now understand how it
works. There are three compartments and two separate pressure relief valves.
The central compartment is where the oil from the oil pump enters, and the
oil normally flows out of this compartment to the external oil cooler/
filter circuit. The oil then returns to the compartment nearest to the prop
from which it flows into the oil galleries in the engine. This is also the
compartment  which contains the  tapped hole  which led to the line to the
old style fuel pump. This compartment will be accessed by an oil temperature
probe placed in the plug holding the weaker spring ( the plug nearest the
prop). This is clearly where the oil temperature should be measured.

Now, the pressure relief valves. The weaker springed value nearest the
prop( think of it as a plugged oil filter relief valve) is between the
central compartment and the compartment nearest the prop. It opens when
there is too much resistance in the external oil circuit and it simply
shunts the oil directly from the oil pump to the engine oil galleries. Not
good for cooling, but it is designed to save the engine in case of a plugged
external oil circuit. Velocities tend to have too much flow resistance in
the oil line to the nose cooler which tends to partially open this valve
leading to cooling problems. This is why PZL has a stronger spring for this
valve and why 5/8 oil lines may be necessary.

Now the valve with the stronger spring fartherest from the prop. It connects
the central compartment to the third compartment in the plate which is the
one furtherest from the prop. This third compartment leads directly back
into the engine oil pan. This valve is normally set at about 90 psi. It is
designed to protect the gaskets and other things in the engine from
excessive oil pressures during cold startups etc. Obviously, this valve will
be closed during normal operations and so there should normally not be any
oil in this third compartment. Unfortunately this is the compartment
accessed by an oil temperature sensor mounted in the plug holding the
"stronger" spring.

The fix is simple, the two plugs holding the springs are interchangeable.
Interchange them and you should get reading very close to that you had in
the old position which should be the correct readings.

Don
----- Original Message -----
From: "Jay Yu" <jayyu@arczip.com>
To: <reflector@tvbf.org>
Sent: Tuesday, May 13, 2003 8:14 PM
Subject: RE: REFLECTOR: Fuel Pressure Reads zero or low/intermittent --
SOLVED




   SNIP
>
> Another thing I noticed is that I now get ~170 degree oil temperature with
> 2500RPM/24"MP. This is 50 degrees lower than what I had before. The
> difference is that I used to install oil temp probe on a tee in between
oil
> bypass group and old style fuel pump and now I installed it in the plug
> where the "stronger" spring is installed. I did see that the oil temp
> increased to more 190 degree while taxiing back to hangar after landed.
>
  SNIP