If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
oil level effects oil pressure
I've noticed that if I run my engine lower on oil than usual (but still
well above the min) my pressure runs lower. I"m trying to understand how oil level effects oil pressure. If there is enough oil to hit the sump, wouldn't the pressure be uneffected? -Robert IO-360-A3B6 engine. |
#2
|
|||
|
|||
oil level effects oil pressure
You are correct in thinking that as long as the oil pickup has a
constant supply of oil the pressure should remain the same no matter the amount of oil in the sump. If you look closer you will probably see that the oil temp is higher. Since you have less oil it circulates through the motor faster and that gives it less time in to loose heat. Hotter oil = lower oil pressure, it's that viscosity thing ya know.... Ben |
#3
|
|||
|
|||
oil level effects oil pressure
wrote in message ups.com... You are correct in thinking that as long as the oil pickup has a constant supply of oil the pressure should remain the same no matter the amount of oil in the sump. If you look closer you will probably see that the oil temp is higher. Since you have less oil it circulates through the motor faster and that gives it less time in to loose heat. Hotter oil = lower oil pressure, it's that viscosity thing ya know.... Ben No doubt that higher oil temperature would result in lower oil pressure. However, unless the engine is running with insufficient oil, I don't see how the oil level would drive oil temperature. In flight, the oil eventually reaches a temperature equilibrium. It cycles through the engine, into the pan, then through the oil cooler. At a given power level, the engine adds X calories/minute (or joules, or whatever) to the oil and the cooler removes Y calories/minute. Eventually, the oil temperature stabilizes at a temperature where X = Y. Oil level doesn't change that temperature. Sure, an airplane with 4 quarts in the sump will reach operating temperature faster than one with 8 quarts in the sump, but the difference isn't that great, and in the end, both engines should end up with the same oil temperature... KB |
#4
|
|||
|
|||
oil level effects oil pressure
No doubt that higher oil temperature would result in lower oil pressure. However, unless the engine is running with insufficient oil, I don't see how the oil level would drive oil temperature. In flight, the oil eventually reaches a temperature equilibrium. It cycles through the engine, into the pan, then through the oil cooler. At a given power level, the engine adds X calories/minute (or joules, or whatever) to the oil and the cooler removes Y calories/minute. Eventually, the oil temperature stabilizes at a temperature where X = Y. Oil level doesn't change that temperature. Sure, an airplane with 4 quarts in the sump will reach operating temperature faster than one with 8 quarts in the sump, but the difference isn't that great, and in the end, both engines should end up with the same oil temperature... KB /////////////////////////// KB, First let me say you explained yourself well. My thoughts are this, if the oil pump can move 4 quarts a minute through the motor and the motor has 4 qts in it then the time spend in the sump/oilpan is minimal. The sump/pan has intake tubes in it and a large surface that dissapates heat as the air passes over the surfaces. If the oil level is low the hot oil coming out of the motor is recirculated right back before it can shed alot of its heat. If there is more oil in the system, then it can spend a little more time in the sump/pan which then will let it loose extra heat. Think of it like this, suppose you had a solar heater for a swimming pool, the thing moves 10 gallons a minute and raises the temp of the liquid passing through it 20 degrees. If the pool holds 100 gallons then it will rise in temp pretty quick, if it held 30,000 gallons by the time all the water is circulated, the surface area will dissapate heat faster then the solar panel can keep heating it. I agree if the pool was perfectly insulated then your temperature equilibrium concept is valid. Am I missing something here?? |
#5
|
|||
|
|||
oil level effects oil pressure
Normally I wouldn't think oil level would affect pressure either.
Might the oil pickup tube (I think your engine has one) be leaking in air where it is attached to the accessory cover, or maybe the oil pump have an inlet leak in it? How about it you engine guys......... |
#6
|
|||
|
|||
oil level effects oil pressure
I used to have an engine that burned a lot of oil. The book said
minimum level was 2 quarts. However, on a couple instances, I got down to about 4 1/2. There was a distinct and consistant drop in pressure at that point. It wasn't gradual, but a distinct drop at a certain level. Always wondered about that too. -- Gene Seibel Gene & Sue's Aeroplanes - http://pad39a.com/gene/planes.html Because we fly, we envy no one. |
#7
|
|||
|
|||
oil level effects oil pressure
wrote in message oups.com... No doubt that higher oil temperature would result in lower oil pressure. However, unless the engine is running with insufficient oil, I don't see how the oil level would drive oil temperature. In flight, the oil eventually reaches a temperature equilibrium. It cycles through the engine, into the pan, then through the oil cooler. At a given power level, the engine adds X calories/minute (or joules, or whatever) to the oil and the cooler removes Y calories/minute. Eventually, the oil temperature stabilizes at a temperature where X = Y. Oil level doesn't change that temperature. Sure, an airplane with 4 quarts in the sump will reach operating temperature faster than one with 8 quarts in the sump, but the difference isn't that great, and in the end, both engines should end up with the same oil temperature... KB /////////////////////////// KB, First let me say you explained yourself well. My thoughts are this, if the oil pump can move 4 quarts a minute through the motor and the motor has 4 qts in it then the time spend in the sump/oilpan is minimal. The sump/pan has intake tubes in it and a large surface that dissapates heat as the air passes over the surfaces. If the oil level is low the hot oil coming out of the motor is recirculated right back before it can shed alot of its heat. If there is more oil in the system, then it can spend a little more time in the sump/pan which then will let it loose extra heat. Think of it like this, suppose you had a solar heater for a swimming pool, the thing moves 10 gallons a minute and raises the temp of the liquid passing through it 20 degrees. If the pool holds 100 gallons then it will rise in temp pretty quick, if it held 30,000 gallons by the time all the water is circulated, the surface area will dissapate heat faster then the solar panel can keep heating it. If you had a 10 gallon pool with the same heat rejection ability as your 30,000 gallon pool, you'd get to the same temperature as your 30k gallon pool. It ain't the mass of the fluid, it is the heat added to or rejected from entire system. No doubt the 10 gallon pool would stabilize at the equilibrium temperature faster, tho... I agree if the pool was perfectly insulated then your temperature equilibrium concept is valid. Am I missing something here?? I would say that regardless of oil level, the sump rejects Z calories of heat per minute (due to the excellent heat conduction properties of aluminum), so it really doesn't matter whether there are 4 or 8 quarts in the sump. If you don't change the radiating area of the sump or the amount of calories you need to reject via the sump the dwell time of the oil in the sump really shouldn't matter in a meaningful way. KB |
#8
|
|||
|
|||
oil level effects oil pressure
I would say that regardless of oil level, the sump rejects Z calories of heat per minute (due to the excellent heat conduction properties of aluminum), so it really doesn't matter whether there are 4 or 8 quarts in the sump. If you don't change the radiating area of the sump or the amount of calories you need to reject via the sump the dwell time of the oil in the sump really shouldn't matter in a meaningful way. KB /////////////////// Hmmmm. I think you just answered your own question. Aluminum is a great conductor of heat, we all agree on that. If you have more oil in the sump the you have a greater area of liquid in contact with the aluminum sump because of a higher oil level. A larger wetted area results in greater heat dissapation...No ????? |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
AOPA Stall/Spin Study -- Stowell's Review (8,000 words) | Rich Stowell | Aerobatics | 28 | January 2nd 09 02:26 PM |
Below sea level | Hilton | Piloting | 13 | June 14th 05 04:42 PM |
Cabin Air Pressure | [email protected] | Piloting | 9 | December 20th 04 03:07 PM |
Attn: Hydraulic experts - oil pressure relief fix? | MikeremlaP | Home Built | 0 | November 2nd 04 05:49 PM |
Date of effect now 1 April 2004 for revised IGC-approval for certain legacy types of GNSS flight recorder | Ian Strachan | Soaring | 56 | December 2nd 03 08:08 AM |