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You can mix mineral and synthetic oil, says company expert

AutoKnow readers have plenty of questions about motor oil. Mike Cassaday, spokesperson for Suncor Energy, which operates Sunoco and Petro-Canada stations, provided the following answers.

  • synthetic oil

AutoKnow readers have plenty of questions about motor oil. Mike Cassaday, spokesperson for Suncor Energy, which operates Sunoco and Petro-Canada stations, provided the following answers.

Q: When changing oil, can I switch between synthetic and petroleum oil, or even mix the two?

A: You can certainly switch back-and-forth or even mix the two types together, if you wish.

The key is to look for American Petroleum Institute certification marks on the label. The API starburst means the oil meets current ILSAC performance standards required by most vehicles sold in North America and the API “donut” stamp tells you the performance level and viscosity grade.

These symbols also certify that the oil completed rigorous testing, including compatibility testing (ASTM D6922), and can be mixed with any other API -certified oil without issue.

API does recommend, however, that you use the same viscosity grade and API service category if mixing brands of oil, in order to maintain performance. That is, only mix API SM-rated 5W20 with another API SM 5W20 oil, whether synthetic or conventional.

Q: I recently bought a new 2009 Ford Escape. I’m old school (age 60) and thought the recommended 5W20 oil was a little lightweight for hotter temperatures or severe conditions like towing my 900 kg boat.

An engine rebuilding shop I spoke with said lighter weight oils are used to boost mileage ratings and automakers don’t care about engine longevity outside the warranty period.

The owner’s manual says I must use 5W20 oil to maintain my warranty. Should I be using a heavier oil?

A: Always use oil of the viscosity grade and performance level called for in your owner’s manual.

While lighter weight oils do improve fuel economy, automakers have also re-engineered their engines to work specifically with these oils.

For extreme weather or operating conditions, consider using a synthetic oil of the grade and performance level specified. These oils resist high temperature breakdown and deposit formation better than conventional oils and provide excellent wear protection even under tough conditions.

Q: My dealership service adviser says that if I use synthetic oil, not to switch back to petroleum oil without first flushing the engine to clean out the synthetic. I’m confused as Petro-Canada has signs saying it’s okay to add synthetic to regular oil if your engine is low.

A: It’s definitely all right to top up with synthetic oil between oil changes. The sign you mention refers to Petro-Canada Supreme synthetic oil, which is an API-certified oil and can be mixed in any proportion with other API-certified oils of the same viscosity grade and performance level.

As stated previously, API-certified synthetic and conventional oils are fully compatible, and fully miscible with each other. No special procedures, such as engine flushing, are needed when switching between the two. So feel free to try synthetic oil, and if you find it’s not for you, you can switch back at any time without added cost or hassle.

Q: A synthetic oil change costs $100, instead of just $50 for regular oil, which I think is an outrageous price.

A: In addition to the benefits mentioned above, synthetic engine oils provide easier cold weather starts meaning less wear on start-up, and cleaner engines through enhanced resistance to sludge and deposit formation.

Eric Lai adds:

Synthetic oils are expensive compared to their conventional counterparts, so the added cost for materials likely accounts for much of the price difference you cite.

Except for some turbocharged or extreme high-performance vehicles, most automakers don’t require the use of synthetic oil to maintain your warranty.

You can send your non-mechanical questions to Eric Lai at Include year, make, model and kilometres of autos cited, plus your name, address and telephone number. Personal replies cannot be handled due to volume.

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