Skip to main content

Skyrocketing gasoline prices certainly have me keeping track of my mpg. I found my classic car is getting much worse fuel mileage than it should be. As frustrating as this can be, poor fuel mileage in your old car is a handy warning that something needs some maintenance. Here are a few things to check.

Wear items: tires, filters, and plugs

Triumph | Tory Bishop via Unsplash

The folks at My San Francisco Car Guys have a great checklist to troubleshoot a car getting poor fuel mileage. The first things to look at are the wear items. These are aspects of your car that you should be replacing regularly anyway. Some items, such as wiper blades and shock absorbers are likely not reducing your mpg. But other wear items may be costing you at the pump.

Begin by checking your tire pressure. Low tire pressure can rob you of mpg. You will probably see the best fuel mileage at the upper end of your manufacturer’s suggested psi. If your tire gets low again, check for leaks.

Another wear item that can destroy your mpg is your air filter. If your engine cannot breathe easily, it may compensate by burning more gas.

Just like your air filter, a clogged fuel filter could conceivably reduce your mpg. So if you are taking a look at or swapping your air filter, see about your fuel filter too.

Finally, worn-out spark plugs can mess with your engine’s timing, preventing it from burning all the gasoline in each cylinder. This means you are pouring unused gasoline out your tailpipe. As you can imagine, this isn’t great for mpg. You can replace your plugs or clean and re-gap your spark plugs.

Fuel and exhaust systems

Ford pickup truck | Evan Wise via Unsplash

Because your fuel and exhaust system are critical for getting gasoline into your engine and exhaust fumes out, a malfunction in either can reduce your fuel mileage. If your fuel filter is good, there are a few more components you can check out.

A bad fuel injector or carburetor is a very common cause of poor fuel mileage. Your old car uses one of these two systems to mix fuel and air and fill each cylinder with this mixture. Fixing either requires advanced mechanical skill. That said, you can mix an injector cleaner into one tank of gasoline and hope this will breathe new life into your injectors.

Both your intake and exhaust system may have exhaust sensors that will likely impact your mpg when they malfunction. Luckily, they should trip your check engine light–if you have one–when they wear out. If you have a check engine light on, have a technician read the “code” corresponding to the light so you know what’s wrong.

Your exhaust system may have other components such as a catalytic converter or muffler that can fail. A leak or partial clog of your exhaust system also will reduce your engine’s efficiency and reduce mpg. This is an important system to have a professional look at.

Driving habits

Plymouth valiant classic car parked on the pavement at twilight with its headlights on.
Plymouth Valiant | Tim Bern via Unsplash

I’ll be the first to admit that driving with a light foot is not nearly as fun. But I can see the difference in my mpg. Accelerating quickly and revving your engine obviously burns fuel. But in addition, keeping your A/C on all the time will burn more fuel. Finally, idling your car for a long period of time eats through gasoline.

There are many mechanical issues that can cause poor fuel mileage. The above list includes a few checks you can do on your own. But if you don’t see an obvious issue, it’s a good idea to take your vehicle to a professional. With the current price of gasoline, a tune-up may pay for itself in just a few tanks.


Can You Really Fit More Gasoline Into Your Fuel Tank When It’s Cold?