Check the fuel spec in your car’s owners manual
by Jacques Gordon
When an intake valve opens, it’s cooled by air rushing past on its way to the combustion chamber. Some of the oil vapor in that airflow (from crankcase ventilation) will stick to the intake valve the same way moisture condenses onto a cold glass of iced tea. The intake valve heats up again during combustion, and as the oil vapor cooks off, a tiny bit of carbon sticks to the valve. As carbon gradually accumulates on the back of the intake valve, eventually the deposit grows large enough to affect engine performance and emissions.
Some engines are more susceptible to intake valve carbon deposits, but the boiling point of the oil itself is also a major factor. The additive package of detergents, dispersants and viscosity adjusters can leave non-carbon deposits too, and so can some fuel additives. In a port-injected engine, the injectors can be situated so they ‘wash down’ the intake valves, but this only helps when the gasoline contains the right mixture of additives and detergents.
The formula for gasoline sold all over America has been adjusted several times over the years to meet EPA tailpipe emissions regulations, and it’s also adjusted seasonally and locally to meet evaporative emissions standards. The EPA also regulates the minimum amount of detergent in gasoline, but when it was first set, many brands already exceeded that standard. Most oil companies reduced their detergent quantity to control costs, making their gasoline less effective at cleaning intake valve deposits.
Several car makers around the world recognized the problem and worked together to find an answer. They formed a Worldwide Fuel Charter that sets performance standards for gasoline, and they call that fuel “Top Tier Gasoline.” It’s a performance standard, not a spec sheet of ingredients, but meeting the standard requires more detergent for cleaning deposits on intake valves, fuel injectors and combustion chambers and less of the additives that can leave deposits. The performance of Top Tier Gasoline is confirmed by independent testing labs (at the additive companies’ expense), so the oil companies are free to develop their own recipe. But the fuel must still meet all other government regulations.
There are over two dozen gasoline brand names in the U.S.A. and Canada that sell Top Tier Gasoline, and some display the “TOP TIER” logo (see the list at http://www.toiptiergas.com). The Top Tier license requires the licensee to sell it through all their brand’s locations and in all their grades. In general, the fuel is a bit more expensive, but meeting the Top Tier standard is completely voluntary, so the prices are still competitive. Whether or not it’s worth the price is a question with several answers. The fuel certainly won’t hurt anything, but some combinations of engine and typical pattern of use may not benefit from the extra detergent. However there is no question that Top Tier Gasoline doesn’t promote deposits and it can definitely clean up existing deposits. Many mechanics and car manufacturers recommend it to their customers.
The port is clean but the valve has an oily carbon deposit. Top Tier Gasoline is designed to clean and prevent these deposits.
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