Curious

[GBBrown]

Wondering about what the service manual says on using 5/40 oil at zero and below and 15/40 above zero.
CAUTION!
Failure to use SAE 5W-40 synthetic engine oil in ambient temperatures below 0°F (-18°C) could result in severe engine damage.
Just what kind of engine damage can happen? Where I live it could be 40 degrees this week and -20 next week, ain't gonna be changing oil every week.

 

[spoon059]

You don't have to change the oil every week. The first number is the "winter weight", or the viscosity of the oil in cold temps. The FIVE in 5W40 means that in cold temps it is thin enough to get early lubrication until temps get up to normal. The FORTY means the oil is thick enough during normal operating temps to provide sufficient lubrication during normal operation.

The difference between the FIVEw40 and the FIFTEENw40 is the cold temp viscosity only.

If you see cold temps, use the colder weight oil. Problem solved.

 

[GBBrown]

So then 5w/40 should be good year round if the 5w is only for start-ups. Ran synthetic 5w/40 in my old Ram for 14 years without a problem, including towing heavy, just can't get my head wrapped around having to use two different viscocities. Heck the New Rams come with 5w/40 in the crankcase.

 

[kthaxton]

They aren't insisting you use conventional 15w-40 in warmer temps, only that you can.

 

[Jonsnow]

I use Rotella 5-40 full synthetic year round.

 

[Cummins12V98]

Personally I run AMZ/OIL 15-40 100% synthetic year round and still would even if -20.

 

[Larry Willard]

All the Cummins pickups come factory filled with 5w40 synthetic, so OK to keep using it year round. I have been running it year round operating in the 80's to 100's for temps with no problems.

 

[Cummins12V98]

They come with 5-40 but they also give a chart to refer to in the owners manual.