Honest Injun!
The SAE paper by Hoult, et. al., was entitled, "Direct Observation of the Friction Reduction of Multigrade Lubricants."
Here is the Abstract:
"The oil film thickness between the top ring and liner was observed using laser flourescence(LF). Five different commercial lubricants, two single [monogrades] grades and three multigrades, were studied at two azimuthal, midstroke locations for five speed/load combinations in a small IDI diesel engine. Cavitation was never observed. The lubricant always separates tangent to the ring surface. The rheology of the oil flow under the ring is consistent with a non-Newtonian viscosity without elasticity. The difference between lubricant type (single or multigrade) corresponds to differences in inlet and outlet conditions. Using an analytical model together with the measured oil distributions, calculations demonstrate a difference in friction between single and multigrade lubricants. The multigrade lubricants have lower friction coefficient, consistent with improvements in fuel economy reported in the literature."
The tests were done using a diesel engine and using laser flouresnce techniques, a calibrated signal measures the film thickness as the ring passes over a quartz window in the liner.
Some excerpts from the study:
"Second, there is a clear separation between both multi and single grades, the single grades showing 1) higher friction, 2) a greater wetted inlet height and length, 3) higher upstream film heights. There is a 30% maximum difference in friction betwee single and multigrade oils."
"Multigrade oils wet the ring less than single [monograde] oils. There is a clear separation of the multi versus single grades according to friction values. The data shows a maximum top ring friction reduction of 20% through multigrade use for the same viscosity, speed and load.
If half of all friction in the vehicle is generated by the ring pack, with one quarter of this generated in the top ring, we estimate a maximum total friction reduction of 1.3% due to multi versus single grade use for the top ring alone. A further friction reduction is expected in the rest of the ring pack too. This result is consistent with industry data which demonstrates a 2-4% savings in overall economy through multigrade use."
"Thus it is plausable that the observed fuel economy through multigrade lubricant use is primarily due to friction reduction in the piston and ring pack."
[ September 25, 2003, 10:57 AM: Message edited by: MolaKule ]