GM has taken a lot of the mystery away but stirred controversy by listing a single specification for all of its gasoline engines worldwide: dexos 1, which replaces four previously differing GM specs and exceeds other oil industry ratings. Dexos 1 calls for additional test methods and strict standards for wear protection, aeration, piston cleanliness, reduction in volatility and oil consumption, and other qualities. You don’t necessarily need to buy GM oil from the dealer; you can choose from a variety of rather pricey alternative dexos 1 products _ very high grade base stock, plus expensive additives and certification and licensing _ that are labeled as GM-approved.
When choosing a motor oil or allowing someone to add oil to your engine, check first in your owner’s manual for specified ratings that might differ from or exceed that of the best API SN, ILSAC GF-5, and ACEA A5 ratings. If lesser or obsolete rated oil was the cause of an engine, turbocharger or catalytic converter failure, a manufacturer may justifiably deny warranty coverage. In some cases, “wiggle room” is practically zero. These newer oil standards bring higher prices but can be offset by longer oil change intervals.
When having oil professionally changed, ask for documented confirmation that the oil being used meets or exceeds standards for your particular vehicle.
If one shop charges more for an oil change than another, it may be for a very good reason.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at firstname.lastname@example.org; he cannot make personal replies.
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