S

Smilin' Jack

Well Known Member
We replaced the crankshaft in our superior IO-360. One of the 241 that the AD was issued for.
Reason for this we fly Angel Flights and did bot want to be sued if something would happen during a flight.

Question. What is your idle Oil Pressure after landing with a warm engine.

I have Dynon SkyView and oil pressure will sometimes go to 35 at approx 600 RPM. Will come right back up to 55 at 750 RPM.

In flight with oil temp 185. oP is 69.

All other indications are great
Appreciate any answers.
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45 is about as low as I recall seeing when I am pulled to idle stop (650) when taxiing with a warm engine.
 
Your valves will be much happier if cruise oil pressure is in high 70's to low 80's. That will raise the idle pressure around 10#.
 
For cruise 55# minimum and 95# max. The new 172's since re start of production measure the oil pressure at the front of the right gallery. So 70# indicated is really 78-80# at the rear of the gallery. This was done to improve valve train lubrication and to keep the operators from freaking out over the "high" oil pressure.
The max oil pressure for warm up is 115#. Previously 100#.
 
jrs14855 said:
For cruise 55# minimum and 95# max. The new 172's since re start of production measure the oil pressure at the front of the right gallery. So 70# indicated is really 78-80# at the rear of the gallery. This was done to improve valve train lubrication and to keep the operators from freaking out over the "high" oil pressure.
The max oil pressure for warm up is 115#. Previously 100#.
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Thanks for the replys
Guess I will crank up the vernenair 1/2 turn
 
We'll dip below 40psi regularly after landing with the RPM in the 500-600 range. I've increased my cruise pressure from 55 to 70-75 and still see the sub 40 dip on landing.
 
Not hijacking the thread since this may be relevant:
-do the engines with piston skirt oil squirter nozzles have a bigger pressure spread between idle and full rpm? Perhaps due to the pressure bleed from the nozzles?
 
andoman said:
Not hijacking the thread since this may be relevant:
-do the engines with piston skirt oil squirter nozzles have a bigger pressure spread between idle and full rpm? Perhaps due to the pressure bleed from the nozzles?
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My engine has piston squirters so that might be a decent theory.
 
Yes, turn in CW to increase pressure.
I’ve owned 3 Lycomings:
- mid time IO-360 angle valve with squirters. The oil pressure was 75 in cruise and 35-40 at idle depending on temp. I used to run the idle rpm at 8-900 to keep the pressure in the high yellow range for piece of mind.
-zero time IO-540 parallel valve that had squirters installed at overhaul. 80 psi in cruise and 45-50 at idle. She runs hot so idle oil temps at shutdown is usually 210 -ish .
-low time IO-320 without squirters. 80 psi in cruise and only slightly lower at idle.
 
The pressure regulator is a ball and spring that unseats once a max pressure is reached. The pressure required to unseat this ball is substantially higher than anything a warm engine will ever see at idle, so any adjustment of the regulator will not be seen at idle. If the ball is seated at idle, then tightening the preload on the spring is only going to keep the ball seated “more” - in other words, won’t change.

Similarly, the piston cooling jets are only active above a certain pressure due to a spring loaded check valve. And since pressure is directly related to RPM in a positive displacement pump like we have in our Lycomings, they should not be flowing any oil at low RPM.
 
Toobuilder said:
The pressure regulator is a ball and spring that unseats once a max pressure is reached. The pressure required to unseat this ball is substantially higher than anything a warm engine will ever see at idle, so any adjustment of the regulator will not be seen at idle. If the ball is seated at idle, then tightening the preload on the spring is only going to keep the ball seated “more” - in other words, won’t change.

Similarly, the piston cooling jets are only active above a certain pressure due to a spring loaded check valve. And since pressure is directly related to RPM in a positive displacement pump like we have in our Lycomings, they should not be flowing any oil at low RPM.
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Flow (from a PD) pump is directly related to pump RPM, thus engine RPM.

Pump discharge pressure is a function of system back pressure which includes any contribution from the pressure reg (relief valve). This (delta) pressure is related to the square of the flow, thus RPM.

All things you already knew.

To the OP. It's never wrong to make sure the ball/seat are clean and in good shape. It's not unheard of to find a score or existing debris which would affect proper seating -> low RPM pressure.

Coil springs suck at keeping a constant force versus travel. One of these days when I have time, I'm going to test replacing the coil spring with a suitable belleville washer stack. In most cases, it won't make a meaningful difference in operation but for a case like the OP's, it could really help maintain a constant oil pressure.
 
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