Allen,
The multi-grade concept is sort of a tough one to visualize. First remember..they don't get thicker as they get warmer, they just don't get thinner, (compared to single grade oil at 0 degrees).
Take a cube of butter and put it in a pan on the stove. There is your 10w oil at 0 degrees.
Turn the stove on. There is your 10w oil at 210 degrees..pretty thin!!
Now we put the magic VI improver (viscosity index) into the oil.
Butter in the pan on the stove. 10w oil at 0 degrees.
Turn the stove on. WOW, butter darn near as thick as it was with the stove off...it didn't get thicker, it just didn't get as thin as it did in the first experiment. Why? because we added a VI improver. Have you heard of "Motor Honey"..it's a VI Improver.
Now why did the old tractor not respond so well to the multigrade...I'll be damned if I know!
A detergent oil only has limited cleaning ability on deposits already in the engine. Its compounds encapsulate and hold junk in suspension until you change the oil. This is why oils have a change life...you can only run it so long then it "gets full" and won't hold contaminants in suspension any longer..BAM, now they start to gunk up the engine.
The general consensus, especially with items like old tractors etc, is if you ran non-detergent, don't switch. You now know all I know about oil, and are qualified for a job at the corner gas station. Have a Merry Christmas Allen.
Stuart
