Originally Posted By: demarpaint
Originally Posted By: autoreign
I've read sometime ago that thinner oil has thicker oil film thickness (at low to mid load) around piston rings due to better flow and thereby providing better seal and better protection. Conversely, thicker oil provides thicker oil film thickness at extreme load (track day, racing).
It is unfortuanate that I could not find the document (a thesis from a university) and I could not find it on the net again.
Could anyone verify this being correct or not?
Shell did a study showing that a 20wt oil did in fact do exactly what you're saying. In engines using oil due to bad "rings" would actually use less oil with a 20 grade than a 40.
Thanks for sending me the article demarpaint.
I went through it and thought of giving a brief summary here for the benefit of others and also for the purpose of promoting discussion.
1) The article seem suggest that the oil flow on the piston rings pack is more likely to flow through the gap on each piston ring to get to the top ring. Hence, lower viscosity oil, being able to flow better, will provide a thicker oil film at bottom of the Top ring,
2) Oil consumption and blow-by is a function of gap width on each piston ring. When Gap on Top ring:Gap on 2nd ring is 3:1, it resulted in high oil consumption and high blow-by. When Gap on Top ring:Gap on 2nd ring is 1:3, it resulted in low oil consumption and low blow-by,
3) Piston deposit is a funtion of oil quality.
That is what I interpreted from the article (The article is mainly pictorial). Conventionally, it seem to suggest otherwise. I would really like to have some expert's opinion on this matter from all the gurus here (particularly on item 1) above.
Thanks in advance.