Maintenance Schedule 'B'

[AlFischer]

Schedule 'B' states: "Follow this schedule if you usually operate your vehicle under one or more of the following conditions. "



Frequent short driving less than 5 miles.

Frequent driving in dusty conditions.

Frequesnt trailer towing.

Extensive idling.

More than 50% of your driving is at sustained high speeds during hot weather, above 90 F.



My question: Driving unloaded, no towing, at 65-70, above 90 F on a freeway with a properly operating cooling system, how would that affect the need to change oil more frequently?



Is 65=70 'high speed'? Seems more like normal speed for today.



It is apparently not a diesel thing as the service manual from DC lists the same conditions for all gasoline engines too.



I have always heard and believed that 'freeway' driving was easy on a vehicle.

 

[DocStressor]

You are fine for the "A" maintenance schedule. The load on the engine increases by the square of your driving speed. So if you were to drive consistently over 80 mph (most folks do where I live), your engine might see high enough temperatures to accelerate oil oxidation. But I've seen enough oil analysis data from the ISB to believe that just about any CH or CI-4 oil will hold up fine for 6 months or 7500 miles, even if you did tow. 65-70 mph unloaded is light duty. But I would not recommend going much over 6 months between changes unless you are using a synthetic oil.