Date: Wed, 21 Nov 2001 19:51:30 -0800 From: Johannes H Andersen <johannes.andersennopsamel.ac.uk> Subject: Re: motor oil
DSJKALLEN wrote: > > A suggestion on weights for your motor oil . . . > > Viscosity Indexers (VI's) are the additives which allow motor oil to have a > wide viscosity range, such as 5W-40 or 10W50. Modern passenger car engines do > not need a 40 weight oil for protection during summer driving conditions. > > Most importantly, a larger amount of VI's are used to create a 5W40 or 10W50 > oil. The greater amount of VI used, the greater the potential for sludge and > varnish formation in the engine. Essentially, you want to look for an oil > with the least "swing" from the low to the high end of the viscosity range. > > I'm not being very technical here, as I haven't looked at my technical docs for > some time. But, for the majority of applications, a 5W30 weight oil (or, even > better, a 10W30) works very well, while reducing the contaminents inherent in > a wide viscosity range oil. > > I've used 10W30 in my '85 900 8-valve since April '85 here in central Illinois. > The temps reach as low as -22 degrees F in the winter and as high as 100 > degress F in the summer. No problems in starting or engine protection . . . > after 142K, the engine is still running fine with excellent compression on all > cylinders. > > Do some research on oil company, and related, websites, and you will discover > that wide viscosity range oils create more problems for passenger car engines > than they solve. Wide viscosity oils are fine for racing engines however. > > Don Just a small comment. Oils such as 10W40 etc are known as multi-grades. In the beginning (of time?) we had single-grade oils. The grade system dates back from the 1920s. A higher grade meant higher viscosity at a fixed temperature, but a standard grading system was introduced that specified a standard straight-line drop of viscosity with increasing temperature to reflect the common behaviour of oils. Multi-grade oils means that the oils behaves as one grade as cold, and another grade as warm, thus jumping across the standard single-grade straight-lines in drop of viscosity with temperature. The effect of this is to *narrow* the range of viscosity, hence avoiding cold start problems from very thick oil, yet have proper protection at higher temperatures. You are right that a larger grade range (narrower viscosity range) means that a greater amount of VI stuff is added. Whether the chemists at the oil companies can cope with this and figure out to remove any ill effect, I have no idea. Johannes
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