Oil grade

[catalinajack]

The bearing clearances and seals were designed to a specific viscosity oil spec.
Old original engines like the oils they grew up with. Deviate from that at your own peril.

What peril. The straight grade oil takes longer to get there. Dry starts is most of the wear.

 

[TBill36]

Maybe a little off topic but from past readings, I thought the benifit of running straight grade oil was so it did not gum up an aftercooler. Apparently the additives for multi-grade will gum up more than staight grade.

 

[catalinajack]

Just had this conversation with Brian @AD. If you not in the bahamas you should use 30. If your in the hot tropics you can go with 40.



He was saying how the multi really messes with oil pressures and has people wondering about there engines conditions.



My opinion being a mechanic, stick with what the master says. And Master Brian say runneth only 30. I run 30.



By the way, don't buy oil from west marine,,, they are waaayyyyyyy over priced. 34 dollars for Rotella t1 30. 17 at WM.

Messes with oil pressures? That is ridiculous. A multi-grade oil at operating temp is of the SAME viscosity as a straight grade oil at operating temp. Brian knows engines. He apparently knows very little about oil.

 

[catalinajack]

I believe one of the manuals for the Lehman blocks (could have been the Sabre versions) had multi-weights in the oil section.

I ran 15W40 for a number of years.... and as many engines do develope an oil leak here and there I switched to 30W then 40W (when I could find it) when I spent longer times in hotter climates. The switch to the single weight was to slow down the leaks mostly because the oil analysis between all the oil weights wound up the same with no recommendation to change.

I don't doubt your experience but how do you reconcile the fact that, at operating temp, a 15w-40 oil and a straight grade 40 oil has the SAME viscosity. In other words, one is as thick as the other.

 

[psneeld]

I don't doubt your experience but how do you reconcile the fact that, at operating temp, a 15w-40 oil and a straight grade 40 oil has the SAME viscosity. In other words, one is as thick as the other.

Only at certain temps.....and saying a modern straight weight is inferior to modern multi weight may need a bit of scientific proof before I believe that.

I believed CAT recommended straight weight for their 2116 engines I believe for some reason back after 2000 or so switching from 15W40.

 

[Action]

In my opinion the multi-vis oil and single viscosity oil will be the same viscosity for a designed weight. Good for oil flow. That is accomplished by an additive package in a muti-vis oil to get that oil to do things (flow) it was not born to do.

My understanding the difference to consider is that a single weight oil is stronger than a multi-weight oil. The stronger oil is better when stress factors are high however it has the downside of a limited temperature range operation. (When an engine is heated up, doesn't really matter what ambient temps are for the most part)

With that said I was aware of this over two decades ago. A lot has changed in oils since then. I keep up with gasoline engine oils and the changes. Not so much with oils in the diesel rating.

One other comment, most gas engine oils never see the type of loading that a multi-vis oil could not handle easily. The exception was the marine gas engine. Those engines operate at higher RPMs for longer periods and always under load. (Moving through a liquid not a gas)

Most recreational marine engines are not operated in freezing or below temps. Unlike cars and light trucks. I would suggest that there are multiple external factors in an oil choice.

 

[Action]

The American Petroleum Institute (API) develops standards. While oil weight is a factor, it is not the only factor. However oil weight is a factor easily understood so it is discussed (sometimes passionately) frequently.

The link below is from the API. You might find it useful.

https://www.api.org/-/media/files/c...-diesel/publications/motor oil guide 1020.pdf

 

[catalinajack]

Only at certain temps.....and saying a modern straight weight is inferior to modern multi weight may need a bit of scientific proof before I believe that.



I believed CAT recommended straight weight for their 2116 engines I believe for some reason back after 2000 or so switching from 15W40.

At certain temps? Isn't operating temp the most important? At operating temp, and probably all the way up, the viscosities are the same. I say inferior cuz mutli-grades get oil to the oil galleries more quickly, less dry metal rubbing together.

 

[Action]

I say inferior cuz mutli-grades get oil to the oil galleries more quickly, less dry metal rubbing together.

Well, that is the deal with newer oil. At least in a gas engine and I would think in a diesel as well. Newer oil grade categories do not fully drain back as much. There is still an oil film left for a very long time coating the metal parts so there is not dry metal on startup.

Action

 

[psneeld]

At certain temps? Isn't operating temp the most important? At operating temp, and probably all the way up, the viscosities are the same. I say inferior cuz mutli-grades get oil to the oil galleries more quickly, less dry metal rubbing together.

Operating temp isn't the only temp when concerned with leaks (which is what I was discussing), not sure my Lehman ever ran at op temp for the multi, and your last 2 sentences seem to be in a bit of a conflict.