7 Engine Oil Myths You Should Stop Believing

Engine oil is one of the most discussed — and most misunderstood — topics in vehicle maintenance. Apex Auto Spare Parts breaks down 7 of the most common myths with the facts behind them.

Myth 1: You Must Change Oil Every 5,000 km

The truth: This rule dates to 1970s conventional oils and looser engine tolerances. Modern full synthetic oils, combined with today’s engines, often have manufacturer-recommended intervals of 8,000-12,000 km. Check your owner’s manual — it’s the authoritative source for your specific engine, not a generic rule.

Myth 2: Dark Oil Means It Needs Changing

The truth: Oil turns dark quickly — sometimes within a few hundred kilometres — because detergent additives are suspending combustion byproducts and keeping them from depositing on engine surfaces. Dark color is proof the oil is working, not proof it’s failed. Colour alone tells you nothing reliable about remaining oil life.

Myth 3: Synthetic Oil Causes Engine Leaks

The truth: This myth has roots in 1970s/80s synthetic formulations that could affect certain rubber seal compounds of that era. Modern synthetic oils are fully compatible with all contemporary seals and gaskets. Switching to synthetic on a high-mileage engine is safe.

Myth 4: You Can Never Switch Between Conventional and Synthetic

The truth: Synthetic and conventional oils are fully miscible (mixable). You won’t damage your engine by switching between them, or by using a top-up of one type when the engine currently has the other. Most synthetic BLEND oils ARE a mix of the two by design.

Myth 5: A Higher Viscosity Oil Gives Better Protection

The truth: Oil viscosity must match the tolerances your engine was designed for. If your engine spec calls for 0W-20, using 5W-30 or thicker will flow more slowly to critical parts during cold starts and through narrow oil passages in modern engines. ‘Thicker is better’ was more true for older, looser-tolerance engines — not for most modern designs.

Myth 6: You Don’t Need to Change Oil If You Don’t Drive Much

The truth: Oil degrades over time regardless of kilometres driven. Short-trip driving — particularly common in Canadian winters — is actually MORE harmful to oil than highway driving, because short trips don’t let the engine fully warm up, allowing fuel dilution and moisture to accumulate. Most manufacturers specify a TIME-based interval (commonly 12 months) in addition to mileage — whichever comes first.

Myth 7: Premium Brand Oil Is Always Significantly Better

The truth: Oil performance is governed primarily by viscosity grade and certification standards (API, ILSAC, ACEA) — not brand name alone. A store-brand 5W-30 meeting the same API SP certification as a premium brand meets the same minimum performance bar. Matching the SPECIFICATION to your manufacturer’s requirement matters more than the label.

Frequently Asked Questions