I wanted to follow up on the recent column on oil changes and motor oil choice. I received a justifiable and polite scolding from shop owner and technical writer John Gillespie, who set me straight on some motor oil facts and suggested topics that need a better public airing. I had said that substituting 5W-30 oil for 5W-20 oil shouldn’t cause any problems, but it can.
Many modern vehicles employ variable valve timing and/or variable valve lift systems to improve engine performance. Pressurized engine oil _ the same oil that lubricates and cools bearings and sliding parts _ is applied via electronically controlled solenoids to precisely manufactured valve train actuators to make the magic happen. Adjustments to valve timing and lift are commanded on an almost continuous basis, and the camshafts and other mechanisms need to respond promptly and precisely for optimum performance.
Motor oil must be clean and of the proper viscosity or the actuators may be sluggish to respond, which will be identified, leading to an illuminated “check engine” light and possible suspension of variable valve operation. This is a somewhat rare possibility, but absolutely worth knowing about. The engine will still operate OK but with reduced performance and economy.
Another area that’s of even higher importance is using an oil that meets exacting standards listed by the auto manufacturer. Many manufacturers specify oil qualities that exceed what’s available in a typical bottle of API, ILSAC, and ACEA-rated name-brand oil. Stricter, more specific ratings by General Motors, Ford, Chrysler, BMW, Mercedes and Volkswagen, among others, can be confusing and should be taken seriously to avoid premature engine failure.
Per John: A 5W-30 that meets BMW’s specs is thicker than a 10W-40, while a 5W-30 that meets GM specs is almost as thin as a 0W-20, telling us the oil industry ratings are fairly loose. Modern, higher-performance engines are subjected to greater stress and have unique lubrication needs compared with low tech engines of the past. Turbochargers and catalytic converters, as well as oxygen sensors can also be negatively affected by incorrect motor oil composition.