I live in Texas, so there’s more heat than there is cold. I currently am running the specified 10W-30, my uncle said it wouldn’t hurt to run 10W-40 as it’s a little thicker. I honestly like the idea, but I like to abide by manufacturers’ specs. What do you guys think? Thank you.

 

Won't hurt anything.

 

I run 10W40 in my 5.9 and live in central VA. No issues whatsoever, even on cold days. FWIW, oil seems much lighter than it did years ago and there doesn't seem to be much difference between 10W30 and 10W40 oil.

 

What brand do you use? I am currently running Valvoline full synthetic, but I can’t find a full synthetic 10W40.

 

It's either Valvoline conventional or Valvoline high mileage. I've had no issues not using a synthetic oil. I'm also running a Milodon 8 quart oil pan, too.

 

On the beater '98 I service with 228k HARD miles I'll fill with 20W50 if I have it. Manufacturer specs are for factory spec tolerances. As the engine wears clearances open up and a thicker oil won't hurt a thing.

Some engine designs need to stay closer to factory specs due to complex valve systems, variable cam timing, etc, but these engines are just old school push rod tech and basic heads

 

And, no knock sensors, some of which can be affected by oil viscosity...

 

Thank you both! I will do my research on both. Only reason I ask is because the engine barely has 60,000 miles, so I’m unsure of viscosity.

 

Stick with the 10W30.