Oil pressure drops, fluctuating
in 912 / 914 Technical Questions
7 years ago
Hello, what would your best bet for a probable cause?
Today I experienced oil pressure drop from normal 3 +- 0,3 bar to yellow arc 1,4 bar and red 0,9 bar for all together maybe 7-10 sec in two-three episodes. Each drop lasted for no longer than 2-3 sec. It took the pressure about 1 sec to drop and about half a second to rise back to normal. This occured in level flight 2-3 min after takeoff.
Pressure has never been above normal 3,x bar when warm, only rises to 5 bar during start with oil at 1 deg C
Conditions:
Rotax 912F/S 600h
OAT 2 deg C
Plane was in the cold hangar for weeks, oil temp at engine start 1 deg C
Oil temp before takeoff 60 deg C, CHT 75 deg C
Oil quant measured at the cold engine at lower limit, above medium range if measured at the warm engine. Thus this may be a reading error due to the viscous oil at the cold start and might be no factor.
This is the second time I ever experienced oil pressure abnormalities.
First time was when I covered too much of the cooling inlet, closed the cooling flap and flew at 75%. Oil became warmer than usual (max 120deg), but that was to be xpected. Then I saw this drop for the first time. Thus higher temps and pressure drop may be a simple coincidence.
There is an oil pressure warning light which I believe is actuated by a switch in the oil press sensor housing, not by the sensor itself. I didn't see the light going on, but as the oil press instrument showed 0,9 Bar only for a second, a short flash of the light might have evaded me, all the more as it's partly blocked by the glare shield.
I could not reproduce the drop during a 15 min ground run after the first occurence, not during a 20 min check flight between the two occurences and not during a 5 min ground run after the second occurence today.
My thoughts:
-A real oil drop dip should not show that fast drop and rise
-Oil pressure sensor (has a reputation for failure)
-cables from sensor to EFIS
-Ground
-the EFIS dispaying the values
-Oil pressure valve (there is a modification kit, IIRC), but don't they cause abnormal high pressure when they fail?
-Air embolism/vapor lock in the oil system? The oil might have collected water which might have boiled - but the CHT was 75deg and the oil temp around 70 deg at the time of occurence (?)
-Oil pump
Problem: checking cables is useful only when real oil pressure is up, which means running engine (dangerous).
I could replace the sensor as most probable cause and quickest route
Any help is appreciated
Today I experienced oil pressure drop from normal 3 +- 0,3 bar to yellow arc 1,4 bar and red 0,9 bar for all together maybe 7-10 sec in two-three episodes. Each drop lasted for no longer than 2-3 sec. It took the pressure about 1 sec to drop and about half a second to rise back to normal. This occured in level flight 2-3 min after takeoff.
Pressure has never been above normal 3,x bar when warm, only rises to 5 bar during start with oil at 1 deg C
Conditions:
Rotax 912F/S 600h
OAT 2 deg C
Plane was in the cold hangar for weeks, oil temp at engine start 1 deg C
Oil temp before takeoff 60 deg C, CHT 75 deg C
Oil quant measured at the cold engine at lower limit, above medium range if measured at the warm engine. Thus this may be a reading error due to the viscous oil at the cold start and might be no factor.
This is the second time I ever experienced oil pressure abnormalities.
First time was when I covered too much of the cooling inlet, closed the cooling flap and flew at 75%. Oil became warmer than usual (max 120deg), but that was to be xpected. Then I saw this drop for the first time. Thus higher temps and pressure drop may be a simple coincidence.
There is an oil pressure warning light which I believe is actuated by a switch in the oil press sensor housing, not by the sensor itself. I didn't see the light going on, but as the oil press instrument showed 0,9 Bar only for a second, a short flash of the light might have evaded me, all the more as it's partly blocked by the glare shield.
I could not reproduce the drop during a 15 min ground run after the first occurence, not during a 20 min check flight between the two occurences and not during a 5 min ground run after the second occurence today.
My thoughts:
-A real oil drop dip should not show that fast drop and rise
-Oil pressure sensor (has a reputation for failure)
-cables from sensor to EFIS
-Ground
-the EFIS dispaying the values
-Oil pressure valve (there is a modification kit, IIRC), but don't they cause abnormal high pressure when they fail?
-Air embolism/vapor lock in the oil system? The oil might have collected water which might have boiled - but the CHT was 75deg and the oil temp around 70 deg at the time of occurence (?)
-Oil pump
Problem: checking cables is useful only when real oil pressure is up, which means running engine (dangerous).
I could replace the sensor as most probable cause and quickest route
Any help is appreciated
