Ask a Mechanic: Learning more about fuel detergents

Dear Ask a Mechanic,

The user’s guide for my 2019 Honda Insight specifies the use of a minimum 87 octane gasoline. It also recommends the use of Top Tier Detergent Gasoline. There doesn’t seem to be one definition for what defines Top Tier in Canada, and it appears all the big fuel producers have their own variations of what detergent additives they use.

I am wondering if an aftermarket additive would be a waste, since the fuel supplied from the big-name gasoline pumps already includes detergent. Also, the instructions for some of these aftermarket additives are very specific about the ratio to use of their product to gasoline. To me this implies there could be some danger of harming the engine if too much is added.

Should aftermarket additives be avoided if you always purchase fuel from a brand name Canadian company that uses a detergent? – Never too clean

Honda is one of several automakers (among the others are Ford, Toyota and Volkswagen) that belong to and support the Top Tier fuel standard program. The program was initiated in the late 1990s by automakers in response to the problems they were experiencing with their then-new fuel-injected models because of the poor quality and low detergent fuels sold at the time. Since then, both Canada and the U.S. have instituted minimum fuel quality standards.

The Top Tier standard calls for a higher level of detergent in the fuel than the minimum standard requires. It also prohibits the use of metallic compound additives in the gasoline. The Top Tier program is funded by participating fuel companies, automakers and fuel additive manufacturers, who obviously benefit from the increased additive use. Several Canadian fuel retailers do participate in the Top Tier program, including Costco, Shell, Co-op and Chevron.

While Top Tier has merit, not participating in the program does not mean other brand name fuels wouldn’t meet the organization’s standards. In my opinion – and as you suggest – simply sticking with brand name retailers means you’re likely to get a quality product with sufficient detergents, precluding the need to add a supplement.

In the early days of multi-point injection systems, some vehicles suffered leaks after overzealous owners (or technicians) used an excessive amount of injector cleaner, damaging the system and its seals. After years of product development and with ethanol-blend fuels now commonplace (ethanol attacks some materials and attracts moisture), modern fuel systems are more forgiving.

Experience suggests that consumer-grade cleaners and fuel additives have varying effectiveness. Should the need still arise, I’d recommend closely following the product’s instructions to avoid any possible negative effects.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. 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.