what engine oil does

[History]

The main purpose of engine oil is to carry heat away. It's other job is to oil the bearings. The oil is part of the cooling system.

Oil flow is important. High flow carries heat away quicker. High oil pressure means a low oil flow. Low oil pressure means high flow.
Pressure is needed to move the oil.

So one can see that high oil pressure is not necessarily a good thing.

The boffins worked out many years ago that on engines 10 psi for every 1000 rpm at 90c temp with a viscosity of zero is the golden numbers.

My Shadow engine runs at 8psi on idle and 43psi at 3000 to 4000 rpm. Relief opens at 43 psi. More or less bang on.

Some engines idle at 25psi and quickly go to 50psi when the revs rise. At high rpm they still are 50 psi because the relief valve opened at lower revs. Oil pumps use engine power and fuel.

Again other views welcome.

Note zero viscosity is at 90c not room temperature.

Bob

[JPB]

Tribology is in the next building to my office, the set up staff in there all wear the pointy hats that you more usually find on chefs, not because they're working with food but because their heads are that shape. One great thing about tribology is that students who come to me - after they've been there - appreciate their workshop time that much more.
Tribologists can make +0.060" pistons fit by talking to a standard block for ten minutes.

But they have their uses as the main campus has one of the most up to date and most comprehensively kitted out tribology labs anywhere in the Berwickshire & Northumberland areas. For example; they can examine some of the £30 per litre 0w/30s synthetic oil that the daily car's engine requires and prove beyond a ribbon of doubt that the £22 per litre oil - that says "approved for Kia, Hyundai and Sipani vehicles using engines from numbers xxxx to yyyy" on the bottle - is exactly the same stuff.

A tribologist told me a joke last week, excuse the brief diversion:





If someone from the metallurgy department had told me that, I'd have had them disciplined, tribologists get away with this stuff because nothing sticks.

[arceye]

John, is it just me do you think? That on the occasions you mention the tribologists I get a mental picture of people in Safari outfits studying little Pygmi people in a lab....... perhaps even prodding them with sharp sticks to cause a little friction

[JPB]

I had to read that twice before it registered, perhaps I need to get up oilier of a morning?

The tribology team members are notoriously hard to spot during the hours of daylight, but I did manage to get the following image from a photography student who captured the shot after laying in wait in a bath of that crappy green "Classic" 20w50, which would have been ignored as it must have been on its way to the disposal facility: -

boffins.jpg (28.68 KiB) Viewed 920 times