Postby Big Z » January 26th, 2013, 6:13 am
CD4, I totally understand why you would want to share that. Some things just can't be bottled up.
gb, your'e still simplifying too much, and considering only once aspect of the whole picture.
Warning: There are lots of simplifications and generalizations in the notes below, but they are presented for explanation.
API, who more or less control the North American oil standards, has been mandating less additives, mostly due to emission standards. SN is allowed less additives than SM, but may actually perform better than SM over its usable lifetime. I am not saying SN will run to a longer than SM, since less addtives (as you have grouped them into detergents, anti-wear and TBN, especially the TBN) will reduce the effective lifetime. This is clearly illustrated with CJ4, where the TBN and ZDDP is significantly lower and of course, CJ4 should only be used in vehicles that specifically require it. But, for want of a better word, the stability of a CJ4 oil is better. It maintains viscousity longer and the NOACK volatility (measure of the rate of burnoff) is superior.
A super useful spec is the HTHS... this is what you actually see on your oil pressure gauge.
This is the little known spec that manufacturers actually aim at. Lots of the Eurpean makers require a high HTHS.
Another nice to have is a high viscousity index... a measure of how the oil viscousity responds to temperature. A higher VI oil does not thin out (and reduce bearing protection) as fast as a low VI oil.
VOAs are nice, but does not give a full guide as to what is going on with your oil.
Ester based oils are naturally polar, so the detergent levels need not be the same as a reformualted Group 3 or a PAO based Group4.
There are just too many variables which are left out, some of them listed above.
