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#4679300 - 02/26/18 10:34 PM When does an engine need the most oil?
HawkeyeScott Offline


Registered: 01/11/07
Posts: 787
Loc: El Oeste
Been snowed in a bit lately and have spent more time (than usual) trying to understand oil capacity and demand. Have a few basic questions:

1. When does an engine demand the most oil? I've always assumed it was at high RPMs.

1a. In a typical engine, does a pump send out more oil at, say, 5000 RPM than 4000 or is there a max output that is reached sooner?

2. In a typical engine/pan, what is the greatest percentage of capacity that is ever in use at once? For instance, in a 6 qt. system, how many of those 6 qts. are out "working" and how many are waiting in the pan to be pumped up into action? ( The origin of this question is my friend's Jeep, after his wife ran it for an extended period with only around 3 qts. in the 5.75 qt. system.)

3. Do some engine designs just require more oil to properly lubricate while in operation? I have owned the Jeep 4.0s that have 6 qt. systems, and now a 5.3 GM that also takes 6. The GM engine is about 25 percent bigger yet their manufacturers required the same amount of oil.

Thanks for enlightening me.


Edited by HawkeyeScott (02/26/18 10:38 PM)

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#4679308 - 02/26/18 10:57 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
Kamele0N Offline


Registered: 02/09/15
Posts: 2098
Loc: Slovenia EU
1) yes...higher rpms needs more oil...dont forget thst oil not just lubricates but also helps to cool down the engine

1a) not familiar about volumetric efficiency of oil pumps

2&3) look on this that way...

The more HP/litre engine has...the bigger sump it needs...add a turbo and it needs a tad of oil more...

Bigger the sump...the easier life oil will have...longer oci
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#4679312 - 02/26/18 11:03 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
BrocLuno Offline


Registered: 09/06/15
Posts: 5621
Loc: Kalifornia Kollective
OK, back in the day - big block Ford engines like FE's would literally starve for oil at high RPM. Drag racing would leave the pumps high and dry. Front sumps and at high RPM they filled the valve covers with oil and the pans were empty. To keep them alive you ran one qt over full. It was usually enough ... Built race engines ran restrictor orifices in the upper end lubrication

Yes, oil pumps are positive displacement. The faster you spin them, the more oil they pump.

At "normal" RPM - say 3,000 - there is about 25% in circulation. The rest is coming back down to the pan, in filtration, or the like. The reserve is there for the occasional blast to 5,000 RPM if needed (say passing).

The MFGs assume that you will be running highway speeds mostly. They give you enough reserve for passing or pulling a hill in lower gears at higher RPM. But they don't spec oiling for sustained high speed use, Except in bigger trucks and police vehicles.

The last bid spec I saw for Calif Highway Patrol is 122 MPH for one hour with A/C and full radio load at 100*F - basically desert highway pursuit. All those engines get increased oil capacity, extra oil coolers, bigger filtration - something to help...



Edited by BrocLuno (02/26/18 11:07 PM)
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#4679315 - 02/26/18 11:09 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
BrocLuno Offline


Registered: 09/06/15
Posts: 5621
Loc: Kalifornia Kollective
And KameleON is right - Oil is the number one component in cooling an internal combustion engine. It transfer heat from surface to surface so it can get to the water jacket. Like piston skirts to cylinder walls to the water jacket.

This is why we pay attention to NOACK


Edited by BrocLuno (02/26/18 11:10 PM)
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#4679322 - 02/26/18 11:21 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
Marco620 Offline


Registered: 02/25/14
Posts: 2220
Loc: Kansan,Heckler Koch fan
In all instances a synthetic oil or blend usually beats dino. A proper cooling system helps too. I would say a higher capacity sump or better lubricant helps. Sounds like a job for Redline Oil or Motul 300V/Neo Synthetic.
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#4679325 - 02/26/18 11:23 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
djb Offline


Registered: 01/16/06
Posts: 727
Loc: Los Gatos CA
Most automotive oil pumps are gear pumps with an adjacent pressure release bypass for regulation. They move a fixed amount of oil per rotation. When the pressure is high enough, a spring-loaded valve releases some of the flow back into the pump inlet.

This isn't especially efficient, and doesn't match the flow needs of the engine, but the simplicity and reliability of a gear pump overwhelms other considerations. If the oil pump fails, the engine doesn't just stop running, it destroys itself.

Most people think of engine oil as just lubricating the bearings. But it's arguably more important as the cooling fluid for most of the engine, and on a tight engine most of the flow is going to oil sprayers. For instance, pistons are cooled almost entirely by an oil sprayer pointed at the bottom. This need for cooling increases quickly with a heavier load, while the bearings have almost a constant flow rate independent of engine load.

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#4679328 - 02/26/18 11:25 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
PimTac Offline


Registered: 03/04/17
Posts: 4628
Loc: Soviet State of Washington
I learned something here. I thought the oil demand was the same regardless of the rpms but higher rpms meant faster circulation of the same volume of oil?
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#4679330 - 02/26/18 11:30 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
BrocLuno Offline


Registered: 09/06/15
Posts: 5621
Loc: Kalifornia Kollective
Bearing side leakage increases with RPM.

Most engines are not squirter cooled as far as pistons go. Only expensive engines, or designs that require it.

Most everyday engines just use sling oil off the crankshaft to lube/cool cylinder walls/piston skirts.


Edited by BrocLuno (02/26/18 11:31 PM)
_________________________
Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.

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#4679334 - 02/26/18 11:41 PM Re: When does an engine need the most oil? [Re: HawkeyeScott]
Kamele0N Offline


Registered: 02/09/15
Posts: 2098
Loc: Slovenia EU
smile

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#4679338 - 02/27/18 12:07 AM Re: When does an engine need the most oil? [Re: HawkeyeScott]
Silk Online   content


Registered: 07/26/03
Posts: 4614
Loc: New Zealand
Sweet - I always think of a splash lubricated engines when we get these complicated topics, people expounding with theory. They just need oil splashing and squirting and squishing to get the job done.
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#4679349 - 02/27/18 01:03 AM Re: When does an engine need the most oil? [Re: HawkeyeScott]
Shannow Online   content


Registered: 12/12/02
Posts: 40173
Loc: 'Stralia
Positive displacement pump shifts the same amount of oil per RPM largely. Thin oil and high discharge pressure affect that, but ignore that for the time being).

What the engine needs is more volume at high RPM, but it's not linear like the pump delivery. A pump htat delivers enough at idle delivers too much at high RPM, which is why the oil pressure goes up, and relief valves are fitted to stop the pressure going through the roof.

The modern way is variable delivery oil pumps, which deliver more flow per revolution at low speeds, and lower the delivery rate per RPM at high RPM/pressure.

Most of the heat that the engine oil has to carry away is actually generated by the oil itself shearing between the moving surfaces. The piston cooling and the like are a minor part of the overall heat that the oil has to dissipate..

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#4679413 - 02/27/18 06:49 AM Re: When does an engine need the most oil? [Re: HawkeyeScott]
kc8adu Offline


Registered: 08/02/05
Posts: 896
Loc: dayton oh
racing/track day.
high rpm and centrifugal force in the turns.
low oil level can be disastrous in a turn at redline if the oil in the pan is too low to keep the pickup submerged.

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#4679477 - 02/27/18 08:42 AM Re: When does an engine need the most oil? [Re: djb]
Claud Offline


Registered: 02/11/14
Posts: 593
Loc: Margate England
Originally Posted By: djb
Most automotive oil pumps are gear pumps with an adjacent pressure release bypass for regulation. They move a fixed amount of oil per rotation. When the pressure is high enough, a spring-loaded valve releases some of the flow back into the pump inlet.


Most pumps are gerotor rather than meshed gear pumps nowadays. They still perform the same function though.

Claud.

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#4679489 - 02/27/18 09:02 AM Re: When does an engine need the most oil? [Re: HawkeyeScott]
FordCapriDriver Offline


Registered: 10/22/15
Posts: 2451
Loc: Balearic Islands , Spain
Overhead valve Vee engines are an example of very primitive lubrication systems that yet work quite well.
Overhead Valve V engines have their camshaft directly above the crankshaft, and the camshaft is lubricated only by the oil that slings off the crankshaft.
That is one of the reasons when breaking in an old school American V8 which has a new flat tappet camshaft, you're advised to immediately raise the revs above 2000rpm, unless you do that not enough oil will reach the camshaft nd the cam and lifters could potentially eat eachother.
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1975 Ford Capri II Ghia 3000 V6, - Shell Helix HX3 20W-50.
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1999 Peugeot 106 II 1.1 Max, On standby

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#4679491 - 02/27/18 09:04 AM Re: When does an engine need the most oil? [Re: HawkeyeScott]
FordCapriDriver Offline


Registered: 10/22/15
Posts: 2451
Loc: Balearic Islands , Spain
And yes, at high RPMS engined to like more oil.
An example is i know racers who use a whole quart/liter of oil more when on the track than on the road.
For example Small block chevrolet V8s and other overhead valve engines need to have oil flow to the top of the engine restricted to prevent all the oil going to the top of the engine at high rpms.
_________________________
1975 Ford Capri II Ghia 3000 V6, - Shell Helix HX3 20W-50.
1988 Ford Escort MkIV 1.6 Xr3i Cabrio, - Comma X-Flow XS 10W-40.
1999 Peugeot 106 II 1.1 Max, On standby

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