Oil weights - 30 vs 40

[Skuza]

For years we've used Penzoil
SAE 30. This year out of curiosity I checked the manual and they recommend SAE40 for air temps above 50F. We always operate in temps above 50 Should I switch?
Also Penzoil has SAE30 and SAE HD30. What gives?
Thoughts?

 

[carterchapman]

Skuza -

Ask a hundred guys/(gals) oil questions and you'll get a 1000 opinions. If you always operate above 50°F, SAE 40HD will be fine. If it goes below 32°F when you operate, use SAE 30 HD (meaning in the Spring or Fall, do you ever operate when the overnight temp is below 32°F). Always use HD - High Detergent - never use 30 or 40 "straight weight"...

My 340 in Georgia uses Mercruiser full synthetic 15W40 HD - per the manufacturer's recommendation. My 410 (With CAT 3126's - cannot use multi-viscosity oil) uses Rotella 30HD due to the cold winter temps in Chattanooga. Even though I have Wolverine Oil Pan Heaters, and my oil temp is always about 95°F, there may be a time when I am anchored out in the cold (and not using AC power for the Wolverine Heaters) so I use 30 WT HD. If I was in Florida, I would use 40 WT HD...

Standing by for 999 other opinions....

 

[Carver370]

Used straight 40 weight since the boat was brand new, usually valvoline, this year I bought rotella straight 40. All of the marinas around me use 40 weight and the crusader manual says to use it too.