People often think small engines equates to lower fuel consumption. In truth, a smaller engine will consume more fuel especially if your daily commute involves a lot of highway/motorway driving.

Here’s why. Say we take 2 cars for a comparison test. Car A, which is a small economic hatchback and has a 1 litre 3 cylinder engine, and Car B, which is a family saloon with a 3 litre V6 engine. The misconception is Car A will be more fuel efficient than Car B, because Car A’s engine is 3 times smaller than Car B. However, if we look at it from a logical point of view, say both cars are on the highway doing 62mph/100kph for 2 hours, Car A’s engine would have been working at say 3800rpm the entire 2 hours, while Car B’s engine did the exact same journey with the engine working at around 2000rpm. Basically, a bigger engine works less to maintain its speed than a smaller engine, and if we’re talking in the context of highway driving, less stress on the engine equals less fuel used.

However, if we’re talking about purely city driving with speed bumps, traffic lights, stop signs, traffic congestion, Car A would likely be more fuel efficient because it has the advantage of lugging around less weight, while exerting similar stress levels to the engine as Car B would (unless you’re flooring the pedal whenever you accelerate). The most important factor when it comes to fuel economy, is not the displacement of your engine, how many cylinders it has, or whether it comes with a CVT/DSG/traditional torque converter/manual gearbox, it all comes down to your driving style and how you actively reduce the stress loads on your engine. Keep the revs low and avoid accelerating when you’re travelling uphill. Learn to plan ahead, accelerate when you’re going downhill, and coast as much as you can.

Maybe replacing the spark plugs. And put some iridium ones

I’m spouting from very old memories here so please google this and verify, but I think Mazda set the range/empty warnings to be extremely conservative because the fuel pump is submerged in the fuel tank and running the absolute full range can cause the pump temp to increase at the very bottom of the tank capacity.

So the useful capacity is less than the actual specification for a full tank. There may be some reduction in fuel efficiency because of the auto being a 4 speed and you driving in a hilly area, but the range being less than expected was a common complaint when the car was new.

Owners would test this by running until the fuel light came on and then filling until the auto shutoff hit the first time (don’t fill into the fuel neck). Whatever that amount of fuel is, is the capacity you should divide by to determine MPG. Back in the day this math, dividing miles driven by actual fuel consumed, returned a fuel efficiency within the expected range.

Some owners then made a habit of driving every tank “past empty” because they knew the warnings were conservative.

What’s the mileage on the car? Have you ever replaced spark plugs? That can make a significant difference to fuel economy. Do you need a new air intake filter or a cleaning of the intake and throttle body? Are your tires properly inflated? Are you carrying around any extra weight? Are you sure your brake calipers are working properly and not sticking? Is your parking brake fully releasing? Is your idle smooth? Have you tried pulling any codes to check engine internals are solid?

Also, if by “ball bearings,” you mean the wheel bearing is going on your passenger side rear, get that fixed. It’s a major safety hazard if it’s going. Could possibly add some drag and hurt your fuel mileage too. Do not delay on fixing a bad wheel bearing.