Why your car’s computer may not be the best oil change indicator

In today’s column we discuss why a vehicle’s computer may not tell you the true condition of your oil and take a look at rustproofing methods.

By Nida Zafar Wheels.ca

May 8, 2021 3 min. read

Article was updated 3 years ago

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Dear Ask a Mechanic:

I have a 2012 Cadillac CTS. Since it was new, I have only driven only 16,500 km. The electronic device in the car tells me that the oil is 75 per cent good. I last changed it on January 31,2020, at 15,787 km. Should I ignore the time span or follow the condition of the oil?  To me, the condition of the oil is more relevant and not the time span between the changes. The dealership agreed with me on one occasion and said I could follow the condition of the oil. What are your thoughts? – Oil opinion

Atif Mohammed, co-owner of Humble Autohaus in Scarborough, said every vehicle manufacturer uses different criteria to calculate oil change intervals and program the OLMs (oil life monitors) of their cars accordingly. Some manufacturers may consider the amount of ignition cycles, time the engine idles and time spent highway and city driving in their calculations. Another manufacturer may use different factors altogether in their criteria.

While the computer provides information on oil change intervals, it doesn’t speak to the condition of the oil. “I would still consider the actual physical condition of the oil rather than (rely on the) computer calculations in this situation,” Mohammed said. You’ll know it’s time for an oil change if the oil is black, smells like gas and looks very thin.

According to the owner’s manual for the vehicle being driven by the reader asking this question, the oil and filter must be changed after one year regardless of what the OLM indicates. It also recommends that the OLM must be reset.


Dear Ask a Mechanic:

There seems to be a major difference of opinion as to what constitutes the most effective rust proofing process for vehicles. Tar-based undercoating is often discredited. Oil spray treatments have been available for some years now with drip-oil treatments apparently superior to the dripless method. However, lately many dealerships have been recommending various types of electronic rust inhibitor modules that are attached permanently to the vehicle’s frame. Which one is the most worthwhile technique, electronic or drip-oil? – Rust proofing  

Mohammed said when he is working on vehicles he sees oil-based rust proofing as being “far more practical,” regardless of whether it is dripless, compared to electronic rust inhibitor modules. This largely comes from his personal experience. Spray oil, done manually, ensures it physically gets into every corner. “We should still stick to old fashioned way of protecting our cars,” he said. Mohammed said he has seen many vehicles with electronic modules that are rusting badly when compared to those protected with a manually applied spray oil.

Electronic rust inhibitor modules work by send a low-power frequency through the metal parts of the vehicle to be protected so it inhibits rust. It does so by activating the anti-corrosive zinc coating used on most steel body panels, according to lab-based analysis. Opinions may differ, Mohammed acknowledged and recommends checking with your dealership to find out what it recommends for your vehicle.


Ask a Mechanic is written by Nida Zafar, a reporter at The Pointer who grew up in a house full of mechanics in Scarborough, and occasionally poses your questions to her dad or brother. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.




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