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3 Things Often Overlooked That Affect MPG

Intake Manifold breakdown

When a car's fuel economy begins to suffer, many DIY mechanics will jump into diagnostics with assumptions that serious problems may be at fault. Sensors are checked, additives put in the fuel, and more. Often, the problem is relatively simple.

At regular maintenance intervals, any good mechanic should be checking the following three items regularly. They are often overlooked for one reason or another.

Air Filter
The air filter (or filters) in a car trap large particulates and items that could hinder the efficiency of the intake system and combustion. Filters are usually changed at regular intervals, often coinciding with oil changes. Sometimes the filter is neglected, though, or it may need changing before its interval due to environmental changes (higher dust, heavy soot or ash in the air, etc).

Changing the air filter is easy, relatively cheap, and fast. On some vehicles, there are multiple intake filters. Make sure you know where yours are located and how to access them.

Intake Ducts
Speaking of air filters, while you're in there, check the duct work in and around the filter. Especially at the intake side (where air is gathered, usually near the grille or scoop). Make sure that varmints or stray pets haven't taken up residence or used your duct work as a stash spot for their nests or food. This happens more often than people might think, even in the city.

You also need to check ducts, especially after the filter on the engine intake side, for leaks or loose fittings. Air getting in after it's been measured (usually by a sensor right at or behind the filter) is not being accounted for by the vehicle's computer. This means a lean condition may be likely, which lowers fuel economy.

Spark Plugs
In today's world, spark plug intervals of 60,000 and 100,000 miles are the norm. But before that interval, they should be checked regularly. I recommend checking plugs every other oil change (roughly 6,000 miles). They are a good indicator of other potential problems when they're just beginning and they can "go bad" for various reasons.

Whatever you do, use the plugs recommended for your car. The owner's manual and (often) a sticker on the underside of the hood or car's firewall will post recommended types. Stick with those. Fancy plugs with claims of longer life and better economy may or may not actually work in your car. The plugs recommended for the engine, and for which the engine was engineered to use, are your best option.