Crankcase oil lefvel during operation

[ledslinger]

How much does the oil level drop when lubricant is sent to all parts of the engine? Does the operating oil level vary drastically with RPM? Do designers like to have the crankcase as full as possible so the level is just barely below the crank counterweights at idle?

I assume the level while running is fairly consistent until a certain RPM is reached that results in the return flow capability being overwhelmed, creating pooling not evident at lower RPMs.

 

[ARCOgraphite]

" .... Do designers like to have the crankcase as full as possible so the level is just barely below the crank counterweights at idle? ...


I see No reason for this on a pressure lubed car engine. The Crank is pressure lubed and piston bore spray/fog lubed by the con rod big ends. You never want the oil level so that the crank dips in it. (windage)/ Certain circumstances it cant be avoided like driving at certain extreme attitudes. Think: Steep hills, High-G cornering, off-roading.

Do you have a concern you wish to address?

 

[LeakySeals]

My 6.0L with 6 qt sump holds 1/3 of a quart in the engine when checking immediately after shut down. 20 mins later, its back to the full line. When I was younger I overfilled an engine by 1.5 qts. Shortly after the overfill, the engine became sluggish and began to struggle, limping down the road. I got out to check oil level and it was a foamy milk shake. So I don't think full as possible is desirable, and the dipstick is below the actual full line to prevent foaming and loss of lubrication. Which is what I assume was happening to me when I rounded a corner.

 

[oldhp]

ledslinger, Depends on the engine. Small block Chevy's at 7000 RPM and higher tend to push oil up into the heads, that is why on drag race or steady high RPM you put oil restrictor's in the camshaft oil galley's. On the newer engines some now have a two stage oil pressure pump controlled by the ECU. At a certain RPM the second stage comes in and pumps more oil to the engine. Engineers know now that you want to control oil flow at all possible RPM's. The most oil is best left in the oil pan. That's kind of the short version but as simple as a oil system is, it's still a balancing act for todays engines.

 

[VeryNoisyPoet]

My car will read nearly a quart low immediately after shutdown with a 6 quart sump. I can see the top end through the fill cap opening with lots of oil pooled on top of lifters which will slowly drain back down. No risk of trapping too much up there, since there are large drain passages. With a steady hand I could dump in a 5 qt jug as fast as it can pour and the level never rises much over the lip around the lifters.

Sump capacity and dipstick min and max marks are designed such that even under high RPM with oil at the min mark, the engine will not starve of oil. That said, running with the oil low will raise oil temperature since the oil spends less time cooling in the sump before getting picked up again, and reduces how much oil is available to dilute and suspend contaminants. The engine will survive just fine with oil and the minimum mark, but keeping it midway and up may be easier on it. Certainly keep it topped off when stressing the engine such as mountain driving or towing.

 

[Omahaug]

Originally Posted By: ledslinger
Does the operating oil level vary drastically with RPM? Do designers like to have the crankcase as full as possible so the level is just barely below the crank counterweights at idle?
I don't think that's what they're optimizing toward (height near crank). The pickup is usually at the lowest part of the pan, it doesn't matter how high the oil level is as long as it is high enough to avoid reaching the pickup.

They also have to engineer oil pan geometry, account for hill driving and oil slosh (usually with baffles to keep oil near the pickup).

 

[djb]

The level drop depends on the engine, but it is often minimal. Oil systems have check valves all over that keeps the oil from draining back into the pan when the engine is off. On an engine I recently rebuilt the initial fill was a bit more than a quart extra over an oil change.

If your check valves leak you might actually be running a quart low.

 

[ZeeOSix]

Originally Posted By: djb
The level drop depends on the engine, but it is often minimal. Oil systems have check valves all over that keeps the oil from draining back into the pan when the engine is off. On an engine I recently rebuilt the initial fill was a bit more than a quart extra over an oil change.

If your check valves leak you might actually be running a quart low.


Check valves "all over the engine" ... probably only one, located at the oil filter (ADBV). That has nothing to do with the oil level in the sump with the engine running.

The oil level in the sump will be the lowest at high RPM of course because the pump is flowing the most. Most high performance car makers say to add 1 qt to the engine for track use, which helps keep the sump level up during high RPM and cornering.

This isn't directly related, but somewhat. My motorcycle has a glass oil level sight window in the crankcase. The bike holds just under 3 qts of oil. When the bike is fully hot and running at an idle (~1000 RPM) the oil level goes down by ~0.4 qt in the sight window. If I rev the engine pretty good, the level will drop even a bit more, then take a few seconds longer to come back to the idle level after going back to an idle. When the oil is colder, it takes longer for the oil to drain back down for the level to stabilize. So doing high revs on an engine with cold oil will lower the sump level more so than if doing the same revs with fully hot oil. The hotter/thinner the oil, the faster it's going to drain back to the sump.

 

[BrocLuno]

Originally Posted By: oldhp
ledslinger, Depends on the engine. Small block Chevy's at 7000 RPM and higher tend to push oil up into the heads, that is why on drag race or steady high RPM you put oil restrictor's in the camshaft oil galley's. On the newer engines some now have a two stage oil pressure pump controlled by the ECU. At a certain RPM the second stage comes in and pumps more oil to the engine. Engineers know now that you want to control oil flow at all possible RPM's. The most oil is best left in the oil pan. That's kind of the short version but as simple as a oil system is, it's still a balancing act for today's engines.


Correct. Back in the 1960's Ford FE engines use to fail racing because they'd pump the sump dry enough to starve for oil. Many 390's went by the roadside due to not enough oil. This was one engine that you ran 1 qt over full IF you were only drag racing. Yeah, it'd whip the oil off the line, but it was not putting rods out the side on the big end

Many mods were built to alleviate the issues. Restrictors, outside supply and drain schemes, etc. With the high and medium riser heads well ported these engines were regularly capable of 6,500+, and at those RMP's the oil pumps were moving more oil than was available ...