Low Viscosity Oil

[Al]

I am running a test to determine if the addition of 30 ml per gallon of gasoline will affect the efficiency of 4 cycle engines.
http://www.bobistheoilguy.com/forums/ubbthreads.php/forums/37/1/Fuels_and_Fuel_Additives:_Gaso

It occurred to me that if 2 cycle engines can run on 75 ml per gallon of gasoline the viscosity of that resulting mixture is around .7 cSts and 20 wt oil is 7 cSts.

Seems pretty obvious that future oils will be in the range of 0W-0 weight. I have read that the future holds at least 0W-4 (TLT magazine).

Fearing 5W-20 oils makes less and less sense (to me). Of course designs will need to change but not by a whole lot.

 

[Shannow]

Al,
There's a little difference (IMO) on what and where the viscosity is being used.

Older 2 strokes were plain bearinged, and used SAE30, non VIIed oil in the fuel...the plain bearings and the piston rings/cylinder walls operate higher than the usual evaporation point for the fuel component, and so are left with a film of lubricant of a fairly high percentage of lubricant, not the average oil/fuel ratio.

Modern have rollers, and the bearings are EHD lubricated...have seen a few systems for roller bearings industrially (queue SKF catalogue for details), where compressed air can be fed into them with a mist of lubricant and there is more than enough oil to EHD the bearings into the forever range of life.

Premix two strokes need enough oil to stop the rings/pistons running dry, but have enough temperature to keep the oil around the rings quite fuel free due to evaporation, and do not want too much oil in the middle of the combustion chamber, where it serves no lubrication benefit, but reduces octane, and pollutes.

Mercedes when they were playing with the Wankel, had a wet spot in the manifold to create a fuel wetted "film" of oil that was introduced on the lip of the (peripheral) port to lubricate the apex seals (piston ring equivalent) without contaminating the bulk mixture.

Two stroke average cst doesn't correlate to 4 stroke sump oil.

 

[Al]

But the point still is that most 2 cycle engines today still use plain bearings and have pistons and rings. So both engines functioned in a plain bearing environment. And even allowing for evaporation viscosity of 2 cycle oil is 20 wt.

I understand what you are saying but my gut engineering feeling is that viscosity of engine oils can decrease. And the April Magazine TLT ( Published by Society of Triboligy and Lubrication Engineers) seems to agree.
http://www.stle.org/research/

 

[cjcride]

This has been discussed here before. The conclusion IIRC is to use synthetic oil for 2 stroke. The ratio was wide yet 100/1 is probably too oil much for a 4 stroke.

 

[Al]

Originally Posted By: cjcride
This has been discussed here before. The conclusion IIRC is to use synthetic oil for 2 stroke. The ratio was wide yet 100/1 is probably too oil much for a 4 stroke.

Not sure you can believe everything, even on Bobistheoilguy. I am tightly controlling the test. If there is no improvement, then a lesser amount under 130:1 is a waste.