01 5.9 with 237K. Do you think it would be beneficial to run 10w40 during the hot summer months in the south?

 

I run 10W40 year round and I'm in central VA. No issues whatsoever and my oil pressure is great, although I did add a high volume oil pump and an 8 quart Milodon oil pan. 5.9 engine is from a used Dakota that currently has about 150,000 miles on it.

 

With that mileage on an old pushrod engine I throw in 10W40 and/or 20W50....the latter perhaps mostly in the summer. You could also easily run 15W40 HDEO and it can be quite inexpensive but slightly problematic as it's almost always sold by the gallon

 

So to this here’s my input….


I rebuilt my 91 Harley engine last year and beefed it up. My bike runs 20w50 oil. So the lifters in the bike are exactly identical to those of a Chevy 350 engine. Same bore size, oil passages in same spots, etc, they looked exactly the same. But after some research, S&S (a Harley upgrade brand that’s very well known) made a video…..4 screaming eagle or S&S or oem Harley lifters are in the $270-300 range. Chevy 350 lifters are like $20 a piece.

So S&S made a video. Two identical engines (Harley engines) one had S&S lifters, one had lifters from a Chevy 350. Both with 20w50 Harley syn3 oil. They filmed in a thermal scope to show temperatures and such. It took the Chevy 350 lifters 6 full minutes before it even began to get to top of engine and cool down. The S&S lifters had oil at top end and cooling working 7 seconds.

the reason for this is because the Chevy 350 lifters are designed for 5w30 weight not 20w50. Because the inside passages are much smaller, top end will get smoked quick. So our trucks call for 10w30 or 5w30 and that’s what the lifters are designed for. So If you run heavier weight oil like 20w50 you run the risk of starving your top and and overheating the components. So in turn I’d use what’s recommended and not go way heavy. Just what my research has told me

 

It used to be that the differences in oil weights was very noticeable many years ago. Today, same as I used to do years ago, when comparing oils with just a basic pour out of the bottle look, it really appears that there isn't a great deal of difference between oil weights these days, other than what's advertised on the bottle. I recall many years ago that 20w50 oil used to pour out of the bottle like a heavy syrup. Today, not so much.

As such, I've chosen to go with 10w40 in the 5.9 magnum engine and haven't had a days bit of trouble with that choice. I do run a hardened & pinned oil pump drive, a high volume oil pump and an 8 quart Milodon oil pan for basic piece of mind for towing. So far, so good.

 

Well i don't know what oil you are referring to but it still pours like that. I have a worn rod bearing and you can hear it at start up so during the hot summer i use 20-50. That's if you can find it! Last two times they didn't have any. Today every thing uses thin synthetics.

 

What I'm saying is that 20w50 oil of many years ago does not pour like the 20w50 oil of today, even when you can find it on the shelf. The oil formulation standards have definitely changed over the years and motor oil is not as thick as it used to be.

 

Decided to try Rotella T6 15w40 since that what I use in my Cummins. Been about 2 weeks and so far so good. Seem to be getting a little better gas mileage too.