You guys are killing me. Slip and Indy are correct.

Read BITOG or call up Redline: The bearing tolerance determines the required operating viscocity, NOT THE ENGINE TEMPERATURE!

The oil bonds open up in multi-vis oil to adjust for the very rapid change in engine temperature from ambient to operating temperature (thermostat). This happens in less than 5 minutes, except under arctic conditions (think Athabaska). Cold, small, tightly bonded, hot open to longer chains.

Once the oil is at operating temperature, the viscocity is what helps keep the bearings from making contact. Too much viscocity over the *bearing gap requirements* just eats up fuel until it can't pump up to fill that particular bearing. If the engine clearances require 30, 50 is NEVER better. Never.

If you have such a worn out motor or crappy design that you need 50W, you are looking at a rebuild. 50W is a kludge from the days before oil coolers and proper engine tolerances. Even NASCAR uses 0 and 5w synthetic because it reduces friction.

I think some of the confusion comes from the stupid labeling used by oil makers. There are many 5w30s that have 40 final viscocilty and 0w40s that have lower final viscocity than the 30s, you have to read up on that particular oil.

 

INTJ Posted on Aug 7 2008, 04:59 PM
This I kinda disagree with.
Viscosity @ 100C is the "final viscosity".
If the oil is labelled SAE 5W-30 then the oil will have a viscosity between 9.3 and 12.5 cSt. @ 100C.
An oil labelled 5W-40 will have a viscosity between 12.5 and 16.3 cSt. @ 100C
SAE makes up the rules, the SAE J300 spec to be exact.
Side note: water (H2O) = 1 cSt at seal level and @ 20C.
cSt = centistoke (wikipedia )
Just to give you an idea what 10 cSt. is.

I think you (INTJ) were trying to say that at temps much lower than operating temp (90-100C) there could be 40 weights that are thinner than 30 weights and vice versa.
Possible but not very likely.
When talking about 0W/5W or 10W-30 oils this IS very possible.
To make sure find product specs and do some calculating to find other viscs then listed by the manufacturer.
Something like this:


IMO: don't use any xxW-50 or xxW-60 weights in the S2000.
Stick to xxW-30 oils.

 

I should have been clearer: A 5w30 can be 12.xx and the 5w40 12.xx at 100 deg C, and you would think that one has higher visc than the other when it is only a trivial difference. The consumer cannot tell which end of the range it is and 9 IS a significant difference from 12.