1. Home
  2. Tech
  3. Tech Q&A: Trailerlife Magazine
  4. Selecting Oil Grades

Selecting Oil Grades

Originally Published in Trailer Life Magazine

Automotive companies universally specify multi-grades in owner’s manuals and SAE 30, which was the preferred oil for GM’s 7.4-liter engine in the company’s motorhome chassis for many years, is no longer listed as suitable.

Owner’s manuals for Ford motorhome chassis and light trucks, for example, list 5W-30 as preferred for gasoline engines in all temperatures and 10W-30 as suitable for temperatures above 0? F. GM light-truck manuals specify SAE 5W-30 as preferred and 10-W-30 as acceptable for temperatures above zero. GM recommends against using any other grades of oil, specifically 20W-50.

Engineers suggest that the viscosity spread 20W-50 is too great, requiring too many additives. Many years ago GM advised against use of SAE 10W-40 for the same reason, although other motor companies continued to approve that grade.Federal fuel-economy regulations also motivate manufacturers to recommend relatively low-viscosity multi-grades. Also, there is the possibility that the vehicle owner who sees heavier oil may neglect to change to a lighter oil for cold-weather driving. Single-grade oils create additional resistance to movements of engine components under all conditions, compared to multi-grades with lower reference numbers. These companies apparently do not believe most motorists are conscientious enough to avoid misusing single-grade oils.

In support of the recommendations, engineers admit that they are motivated by fuel-economy considerations in vehicles with a gross vehicle weight rating (gvwr) of less than 8,500 pounds, but add that they are convinced the latest lightweight multi-grades carrying the starburst symbol will protect engines under extreme operating situations. One veteran engine-design manager admitted he had always favored thicker oils for hot-weather situations but was won over by his own engine durability testing with the lower viscosity oils.

This Article provided by The RV Handbook.

Travel Trailer How To

The Best of RV Magazine Delivered to your Inbox

Subscribe to RV.com and RV Magazine

Subscriptions starting at only $14.97 per year.

Members save by only paying $9.97 per year!

logo

Please login or register to view archived articles.

Sign In

Do not have an account? Create New Account

Menu