2300 Hours, Should I go thicker?

manyboats said:

Tom B wrote;

"I am guessing this is a type-o? SAE30 or 10W30 is thinner than 15W40. Right?"

Depends on at what temperature. The 15W-40 is thicker at high operating temps and thinner when starting up cold.

Click to expand...

Google the temperature / viscosity graphs. If its thicker at high temps (200), it's thicker at low temps (50). It seems squirrelly to me to imagine a cross-over.

Am I missing something?

I think I'm going to have to dust off my old fluid dynamics book.

It's a more "modern" oil....probably designed for higher performance apps ...so why not?

Perhaps because there is less OIL in the oil?

"Modern" detergent oils contain loads of chemicals 15%+ which are to help the oil do its tasks.

As the oil has to work harder in more modern engines , higher operating temps , higher loads and the burden of dumping exhaust gas back into the intake EGR , for the air police the oil has to do far more .

So the additive package is larger , with less oil doing the lubricating.

This may not be all bad as most of our non EGR engines are so underloaded that help in removing or suspending carbon for the filter to grab may be a good deal.

Same deal with the flour (thickeing agents ) put in multi grade oil.

Thin oil with something to temporarily clump it together is not my (or many users) choice of lubricant.

Yes it scrapes off easier (being thinner) so there is a mileage gain , and for some it will help in cold starts .

Cranking 5 seconds instead of 2 is hardly an advantage that would have me abandon single weight oil.

Should there be a lubrication problem , I prefer more OIL in my oil , as it might be a help.

Ben said:

Google the temperature / viscosity graphs. If its thicker at high temps (200), it's thicker at low temps (50). It seems squirrelly to me to imagine a cross-over.

Am I missing something?

I think I'm going to have to dust off my old fluid dynamics book.

Click to expand...

Ben,
Thicker than what is the question. 15W40 oil is SAE15 weight straight oil with additives in it that cause the 15W oil to be as thick as straight 40 weight oil at 178 degrees F. There's no 40w oil in it.

When its cold 15W40 is thinner that SAE30 and when it's hot W15-40 is thicker than SAE 30. This is true only if the viscosity improvers are working
well and not "worn out".

FF says "So the additive package is larger , with less oil doing the lubricating." and "I prefer more OIL in my oil". As do I and this is the main reason I use straight weight oil.