oil level question

[mosp]

I was chatting with a guy at work today who was convinced that engines are designed so that if the oil in the sump is enough to reach the "min" level on the dipstick then that is sufficient to offer maximum protection to the engine, the rest (up to the max) just a safety buffer to allow for use/drop in level. I was of the opinion that it would be "ok" to run with the level at min, but for maximum protection/running it would be designed to run when at the "max" level. Obvioulsy neither of us are daft enough not to top up when needed and certainly will not be running any long term "lets run it on min and see what happens" experiments!

So - PH massive, which of us is right?!

Cheers,
mosp

[Prof Prolapse]

No basis for this other than a bit of lateral thinking but I'd expect to have full protection from the minimum point.

Afterall you're told to make sure you keep the oil between those markers. Not to have it constantly full.

If you were supposed to have it full why not have a bit more capacity built in. Just in case!

[Burny16v]

I'd say both of you to an extent. Obviously the minimum marker is sufficient for full protection, otherwise the min. marker would be higher up! But you'd have to be careful it didn't drop significantly below it. You'd also have to be careful trying to get it to the 'max' limit that you didn't go very much over max as well, as that's not particularly advisable either!

I aim to get it between min and max, so there's a bit of a buffer either way...can't be bothered playing the game of trying to get it to one of the lines!

[Life Saab Itch]

From personal experience the min mark is fine too run on as long as you don't get any significant G-loadings through the car. When you only have the minimum amount of oil in the sump it tends to fk off away from the strainer to the outside of the sump. This isn't a problem if you are off the throttle doing low revs, but if you have your foot in, you will fk the engine pretty damn quick.

[Athlon]

You would be very suprised how much oil gets pulled from the sump at full revs! I would not risk running at max rpm with only the min in the sump, yes it is returning all the time but not always as fast as it is getting sucked out!

[Ozzie Osmond]

Fair points, but when you think about there's nothing especially magical about any specific oil level. The only certainty is that the engine NEEDS oil and it needs it at PRESSURE.

Cars get driven on hills, parked on slopes and subjected to acceleration/braking/steering forces so there has to be some leeway.

• You mustn't let the oil level get so low the pickup sucks air and you lose oil pressure.
• You mustn't fill the oil level so high that the crankshaft and conrods are dipping into it, suffering unwanted stresses and whipping the oil into an aerated froth.
• You need enough oil in the engine to allow it to do its cooling job effectively and enough that it doesn't suffer excessive use between scheduled services. If you think about it, half as much oil would have to do twice as much work.

In summary, it doesn't much matter whether the oil is at min', max', between the two, just under or just over....

[spikeyhead]

Athlon said:

You would be very suprised how much oil gets pulled from the sump at full revs! I would not risk running at max rpm with only the min in the sump, yes it is returning all the time but not always as fast as it is getting sucked out!

You can generally get away with bring well below the minimum mark. There's so many tolerances allowed for that it's rare that they all stack up against you.

[Ozzie Osmond]

Athlon said:

it is returning all the time but not always as fast as it is getting sucked out!

That has to be nonsense. Otherwise an engine would suck its sump dry under sustained high rpm, lose oil pressure to the bearings and destroy itself in seconds.

[mosp]

Thanks for all your replies - I think that Ozzie Osmond's comment about the oil getting used more and "working harder" was where I was coming from with my tain of thought.

I might tell my mate that he was pretty much right, but then again - wheres the fun in that, it will only make him (more) cocky

Cheers,
mosp

[jeebus]

Im sure that on a lot of cars it is only a litre of oil between min an max, I stand to be corrected though. Also the Lancia Delta Intergrale used to have a quirk that if the oil level wasn't kept on top of it would starve itself in hard corners and the crank could give up the ghost after a few thousand miles.

[maniac0796]

Minimum is the, as stated, the minimum your engine can run on without being damaged. Maximum is the maximum. Any point inbetween there is fine. Above max does damage and below min does damage.

However, depending how good/bad the baffeling in your sump is, you might get the oil pressure light to flash up if you go round a corner fast enough with it on the minimum.

[JohnnyJones]

There's no way I'd run a car on track with the oil lower than the max on the dipstick.

The drift car (200 sx) is always 5mm over the max.

[Fleckers]

who is going to be the first person to say DRY SUMP ?

ok must be me

bit ott on a road car but I was young and had money and it was more than slightly cool back in late 80's / early 90's

also back then I drained over 12L of oil form a car I was asked to look at as it would not run, it had oil in it, right up to the top of the engine, you could see it through the oil filler cap, when I pulled dipstick it gushed out all over the place

[Ed.]

If a car is filled to the minimum then is probably is safe because there is a safety margin. If you let the oil level fall to the minimum its clearly losing or burning it somewhere, less there is quicker it burns so not really a good long term strategy.

[anonymous-user]

My mate did engine develoment for Austin (Old guy) he says the only way they set the oil level ona new engine was to run it on the test bed to the point it stopped using oil and that was the max on the dip stick. No calculation for protection,
Calcs I've done on my Lotus 900 series race engine, using the oil pup capacity are that sumpm empties in obout 30 seconds at 7500rpm, so oil return is more important than volume,
My thought are logically providing there is oil for the pump pick up and the temp is OK the level in the sump is uniportant in itself
But if your planning along trip more oil to keep the temp down,
Having said that what my cals say my heart says run it ful, my race car is run nerly two litere over as more than this and I get the crank spalshing at start up, never had a problem with two much oil.

[Athlon]

Ozzie Osmond said:

Athlon said:

it is returning all the time but not always as fast as it is getting sucked out!

That has to be nonsense. Otherwise an engine would suck its sump dry under sustained high rpm, lose oil pressure to the bearings and destroy itself in seconds.

Really? I have seen exactly that happen on a 289 Ford V8. We always ran the engines on cars used on the drag strip with an extra litre over max because they would be running very low indeed at the end of the run.

Read a copy of the Chrysler engine upgrade book and they will tell you the same thing. In reality a road car will not run at max rpm/throttle for long enough to pull all the oil from an underfilled sump and never from a full sump but race cars have dry sumps for a reason.

[chard]

Oil return when cold is much slower.

I had a car if run on minimum. A couple of mins after a cold start, pressure would drop to zero for a few moments before returning to full pressure and being OK for the rest of the journey. I guess oil grade could also effect this.

[liner33]

Athlon said:

Ozzie Osmond said:

Athlon said:

it is returning all the time but not always as fast as it is getting sucked out!

That has to be nonsense. Otherwise an engine would suck its sump dry under sustained high rpm, lose oil pressure to the bearings and destroy itself in seconds.

Really? I have seen exactly that happen on a 289 Ford V8. We always ran the engines on cars used on the drag strip with an extra litre over max because they would be running very low indeed at the end of the run.

Read a copy of the Chrysler engine upgrade book and they will tell you the same thing. In reality a road car will not run at max rpm/throttle for long enough to pull all the oil from an underfilled sump and never from a full sump but race cars have dry sumps for a reason.

Thats because the oil rushes to the back of the sump under prolonged acceleration , used to put a "gate" in the sump of the dragbikes for the same reason its not that the oil is in the head just that its not near the pickup

[Sam_68]

Life Saab Itch said:

From personal experience the min mark is fine too run on as long as you don't get any significant G-loadings through the car.

It depends on the specific car, of course, but I used to regularly get the oil pressure warning light coming on on my last company car (Skoda Octavia vRS) during hard cornering, well before the oil level had reached the 'minimum' mark.

Best to play safe and keep it topped up to the upper mark.

[RossB_eg4]

Sam_68 said:

Life Saab Itch said:

From personal experience the min mark is fine too run on as long as you don't get any significant G-loadings through the car.

It depends on the specific car, of course, but I used to regularly get the oil pressure warning light coming on on my last company car (Skoda Octavia vRS) during hard cornering, well before the oil level had reached the 'minimum' mark.

Best to play safe and keep it topped up to the upper mark.

Basic and correct advice IMO. The two marks upon the dipstick are the 'safe' points for what the car is most probably going to be used for, ie your Mum isn't going to be pulling 0.5g in any plane driving to work or the shops.

However if you're an enthusiastic driver or do any track time i'd suggest keeping the level up at the full mark, some would even say a litre above full if you're not running any baffle plates; so to avoid any drop in oil pressure when you are most probably at maximum attack; when the engine will lunch itself and spit the remnants out the side of the block.