ems@amdahl.UUCP (ems) (12/31/85)
I have received mail from several folks on the question of mixing different vicosities of oil. The consensus? There is no way of predicting the final outcome. The viscosity is a product of the oil base and additives. Even from a single manufacturer mixing different bases and additives results in a new, unique, mixture that can be measured but not predicted ... Looks like I will have to look for another synthetic 10w40 ... I know Amsoil used to make one. Do they still? Are there other 10w40 synthetics that have done a good job for you? Thanks for the replies, -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems This is the obligatory disclaimer of everything.
joe@dual.UUCP (Joe Weinstein) (01/07/86)
Hi. Some facts about oil viscosity and mixing. 1 - The effect of one viscosity oil on another is not linear! A lower viscosity oil will bring down the viscosity of the mix even in small percentages. Contrastingly, You have to add so much thick oil to thicken a mixture that you would need bathtubs and bathtubs full of 40 wt. to bring a quart of 30 wt. up to near 40 wt. You can test this with a cup of 30 wt. and some 3-in-1. This means that topping up with a heavier oil is OK. As soon as they mix the viscosity will be what you had before. 2 - The listed viscosities on cans are in fact ranges which can OVERLAP! One dealer's 30 wt. might be sold as 40 wt. by another! 3 - Oil breaks down with ( time X high temperature ). A major factor in the temperature of an oil in an engine is the viscosity. A thicker oil gets hotter owing to shear forces than a thinner one. All oils break down at the same temperature. Therefore you should use the lightest oil recommended by the engine manufacturer. Especially after break-in where surfaces are smooth. The additives are more important than the viscosity. Use only the best grade ( SF ). Also, molybdenum add ins work to coat surfaces and protect them during start-up before the circulation system gets oil there. Start-ups account for a lot of the wear of a broken-in engine so moly is a good bet. Joe Weinstein
smh@mhuxl.UUCP (henning) (01/11/86)
**** **** From the keys of Steve Henning, AT&T Bell Labs, Reading, PA mhuxl!smh > 3 - Oil breaks down with ( time X high temperature ). > The additives are more important than the viscosity. > Use only the best grade ( SF ). Also, molybdenum add-ins > work to coat surfaces and protect them during start-up > before the circulation system gets oil there. An oil execuative told me that the multi-viscosity additives break down ususlly in the first 1000 miles. He prefered single weight oils since he knew what his viscosity was for at least 2000 miles.