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stratobee
Joined: 28 Dec 2010
Posts: 159
Location: Los Angeles
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 Posted: Fri Jan 06, 2012 12:11 pm Post subject: Oil pressure low hot idle. |
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I was reading Moe's response in another unrelated thread:
| Quote: | | Generally, if the engine is very worn with lots of clearance between the worn parts, which allows the oil to escape back into the sump using the path of least resistance, your biggest problem will be at hot idle (low oil pump speed and lots of clearance for the oil to squirt out at). When I had two very worn engines in my bird the oil pressure would barely stay in the green in the air, however, on the ground and hot there was not enough oil pressure (below 35PSI) to make the fuel metering system work, so it would run so rich that it was hard to keep it lit when landing, and you had to manually lean it out on the roll out. |
And that's exactly how my engine behaves. When's she's really hot and has been running for about 1hr, the oil pressure drops just below the green arc at idle, but never in the air. Also, the right engine can quit when you throttle back at high altitude landings on rollout. It's happened to me twice as I tried to taxi away only to find the right engine not turning. Now, that could have something to do with pressure carb, but then again it could not. Could this be related?
But what I don't understand is what has the oil pressure got to to with the fuel pressure/mixture? Is it right of me to assume that they're unrelated, or is the low oil pressure at hot idle a sign that my engine might need an overhaul soon?
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cschuerm(at)cox.net
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| Posted: Fri Jan 06, 2012 4:03 pm Post subject: Oil pressure low hot idle. |
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stratobee wrote:
| Quote: | is the low oil pressure at hot idle a sign that my engine might need
an overhaul soon?
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That's pretty much exactly what it means. On your GO435's, the oil
pressure has nothing to do with mixture control. That's an issue for
the Simmonds injected engines. You're probably due a carb overhaul.
One the diaphragms start to get hard, mixture control begins to get
unreliable. Suggest Mikes A/C fuel metering in Tulsa, OK. He's the
pressure carb guru and has all the strange flow bench stuff to set one
up properly.
Chris
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moe-rosspistons(at)hotmai
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| Posted: Fri Jan 06, 2012 7:32 pm Post subject: Oil pressure low hot idle. |
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HI Adam,
The information that I listed is indigenous to the IGSO 540 B1A or B1C. These engines have Simmonds fuel injection units on them. The system is a single point injection system with only one large nozzle that sprays directly into the gear driven supercharger on the rear of the engine. This system uses oil pressure to operate a mechanical computer that is in the same housing as the fuel pump. The idea is that the system will compensate for density altitude (sort of). When the oil pressure gets low (below about 35 PSI) the pump gasoline pressure overcomes the metering device and causes too much fuel to flow to the nozzle for the amount of air that is being flowed through the supercharger (sort of). I have not ever come across an internal combustion engine with carburetors that used oil pressure in any way to meter the amount of fuel being fed into the engine. If anyone is aware of one let me know about it. From an engine running standpoint the worst combustion problem brought about by high oil consumption is the fact that the oil which passes by the rings or valve guides will lower the octane rating (sort of) or the fuel/air mixture in the cylinders and can cause pre-ignition. If you run the engine extremely rich to get rid or the pre-ignition you may go into detonation.
Hopefuly I have confused you sufficiently.
Regards,
Moe
N680RR
Former proud holder of the Golden Pedal Award
Current Holder of of the Fartest Flown Award
Current Holder of the Purple Boots (although I haven't had the nerve to wear them in public)
| Quote: | Subject: Oil pressure low hot idle.
From: adam(at)adamfrisch.com (adam(at)adamfrisch.com) D
Date: Fri, 6 Jan 2012 12:11:13 -0800
To: commander-list(at)matronics.com
--> Commander-List message posted by: "stratobee" <adam(at)adamfrisch.com>
I was reading Moe's response in another unrelated thread:
> Generally, if the engine is very worn with lots of clearance between the worn parts, which allows the oil to escape back into the sump using the path of least resistance, your biggest problem will be at hot idle (low oil pump speed and lots of clearance for the oil to squirt out at). When I had two very worn engines in my bird the oil pressure would barely stay in the green in the air, however, on the ground and hot there was not enough oil pressure (below 35PSI) to make the fuel metering system work, so it would run so rich that it was hard to keep it lit when landing, and you had to manually lean it out on the roll out.
And that's exactly how my engine behaves. When's she's really hot and has been running for about 1hr, the oil pressure drops just below the green arc at idle, but never in the air. Also, the right engine can quit when you throttle back at high altitude landings on rollout. It's happened to me twice as I tried to taxi away only to find the right engine not turning. Now, that could have something to do with pressure carb, but then again it could not. Could this be related?
But what I don't understand is what has the oil pressure got to to with the fuel pressure/mixture? Is it right of me to assume that they're unrelated, or is the low oil pressure at hot idle a sign that my engine might need an overhaul soon?
--------
Adam
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=362598#362598
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