Engine Oil Volumes and Retention Time

Status
Not open for further replies.
Joined
Aug 12, 2012
Messages
575
Location
Saskatchewan, Canada
Another topic to ponder and looking for input.

Let's say again, we have a typical passenger car or truck operating normally. Let's assume that to get to the full mark on the dipstick it requires 5 quarts (4.732 L) of oil.

With the engine in operation, some of the oil will be in the oil pan and some of the oil will be in the engine's moving parts. Out of the 5 quarts, how much will be in the engine and how much will be in the oil pan (assuming steady state)? Is it small, say like 0.1 - 0.2 quarts? Or even less? Or would it be larger, say 1 - 1.5 quarts? Or even more? The oil filter volume comes into play here too.

Furthermore, what are typical retention times for oil in the oil pan? Is it correct to assume that it varies with engine RPM as I think most oil pumps are driven mechanically off the crankshaft?

Looking forward to reading people's thoughts.
 
Last edited:
I've seen a SBC take 3 qts to put it on the full mark. No oil pressure problems showed, no idiot lights. The oil pump pickup is approx 3/8" off the bottom of oil pan, so at least there was that much in there. No idea what size oil filter was on it. So by that, there must be pretty good drain back.
 
Excellent question, i've pondered myself. Every year, make, model, will have varying design...
 
Many variables,
engine design, oil vis, engine rpm, oil pump volumes, clearances, operating rpm, ability for the oil to drain back to the sump to name a few.,
 
Every engine is different. But you are on the right track. Keep in mind that when you do an oil change, you are nowhere near replacing all the oil in an engine.

For example, My Outback takes 5.1 quarts at each oil change to fill the crankcase and filter. But total oil capacity is 6.9 quarts. My SL550 takes 9 quarts for an oil change. But from what I have read, I believe total oil capacity is just under 12 quarts. So I would estimate 2-3 quarts of oil remain in the oil pump, galleys, and internal oil lines of the engine.

This is why I am always entertained by those who, when doing an oil change, let the oil drip for a very long time in hopes of getting that last little bit. That last BIG bit never comes out. Not unless you did a total engine tear down.
 
Last edited:
I would be surprised if more than 25% of the oil is actually up out of the sump at any given time. What I'd be more interested in is how quickly it turns over its capacity. Every one minute? Five minutes? Must vary a lot depending on engine speed.
 
Why does this matter? It is designed to have ample oil capacity and oil level is checked engine off after a few, enough seconds that the majority has drained back. You're not going to have a problem with a level off by a small fraction of a quart that's still in the engine.

Oil filter doesn't count, assuming a drain back valve (or even if there isn't) the dipstick full mark should match the rated capacity of the system with the oil filter on. If you've just done an oil change and were measuring with the filter empty, run the engine and measure again. Different engines, different filter sizes, there's no use in trying to nail down some # of ounces but if you really want to measure it, that's up to you. Having measured it doesn't change the need to run the engine after a change and top it off if needed.
 
Last edited:
Originally Posted by Jimmy_Russells
I would be surprised if more than 25% of the oil is actually up out of the sump at any given time. What I'd be more interested in is how quickly it turns over its capacity. Every one minute? Five minutes? Must vary a lot depending on engine speed.



I don't have a figure for a car but according to a BMW publication, my 40 year old BMW motorcycle recirculates it's 2 litres of oil 6 times per minute at 3400 rpm which is only a moderate cruising speed.. You can double that at maximum revs. It's an unusually high flow rate, so much so that when they are raced the oil pump consumes too much power and has to be modified.

At a guess I would think a car recirculates at least once per minute when cruising.
 
All about engine design and drain-back access and passage size. The old FE Fords running in drag racing would pump the pans dry at 6,500 in 1/4 mile. That was a 5 qt system. So if you were really racing (not fooling around on the street), you ran them a qt over full at the start and you'd have oil pressure going out the big end.

You could massage the system and relieve the drain-back passages from the heads and you could make them manageable. But that was a whole lotta work and meant a torn down engine. Easy enough to do if you were porting the heads anyway ... Easier to run high oil volume on near stock engines
smile.gif
 
Originally Posted by BrocLuno
All about engine design and drain-back access and passage size. The old FE Fords running in drag racing would pump the pans dry at 6,500 in 1/4 mile. That was a 5 qt system. So if you were really racing (not fooling around on the street), you ran them a qt over full at the start and you'd have oil pressure going out the big end.

You could massage the system and relieve the drain-back passages from the heads and you could make them manageable. But that was a whole lotta work and meant a torn down engine. Easy enough to do if you were porting the heads anyway ... Easier to run high oil volume on near stock engines
smile.gif




This ^

C5 and C6 Corvette owners manuals state if you are going to track the car to run it 1 quart overfilled.

Most cars can run higher RPM sustained without pumping dry, however enter in corners and high RPM in a wet dump system and you could run the pan low.

It's more of an Issue with a SOHC or DOHC engine, or one with a large Head design like the old Ford FE. The original lotus Built LT5 ZR1 engine had huge heads and could trap a lot of oil in them.

Back when I used to race my 4G63 Turbo eclipse I would overfill it about 1/2-3/4 quart before a night of long roll runs. (those were my dumb days of racing).
 
Last edited:
Status
Not open for further replies.
Back
Top