Why heat up multi-weight oil before changing?

[rdbonds]

Thanks, Now this makes sense.

That chart is very revealing as to why to use multi-weight. Is the 15W-40 chart example for Rotella T6?

I like the idea of pouring some clean oil in to clean out the bottom. Seems like I always have a little oil left over from various changes. The cans just sits there just waiting for something! Now I know how to put the left overs to good use.

I remember in the "old days" you could buy flush oil or sometimes just run coal oil for a few minutes to flush out the engine and sump. That was when everything was single weight dino. Sort'a makes me sound like a dino!

Thanks again

I'm not sure which specific oil the chart was referencing...sorry about that. I just grabbed a generic visual that illustrated the concept.

I once had a lab class that had us using a rotating drum viscometer to test various SAE oils at varying temperatures and back-calculate which oil weight the sample was. JUST about the time we thought we had it down, the instructor tossed in a mystery sample (a multi-weight) and screwed everyone up.