Why is my car getting bad gas mileage all of a sudden?

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asked Jul 3 in Other-Cars/Transportation by spoonerrigger (1,280 points)
Why is my car getting bad gas mileage all of a sudden?

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answered Jul 5 by Prigen (13,320 points)
If your car is suddenly getting bad gas mileage it can be caused by bad spark plugs, clogged fuel filter, clogged fuel injectors, dirty throttle body, carbon buildup in the engines intake and exhaust valves, bad spark plug wires, bad timing chain, bad timing belt, bad head gasket or a host of other things.

If your engine is misfiring then it can also lead to poor fuel mileage.

The difference between city mpg and highway mpg is that with city driving you do a lot of stop and go driving which uses more fuel and on the highway you usually keep at a constant speed which uses less fuel to go further miles.

City mpg generally is the lowest mpg rating for a vehicle primarily because of the frequent starting, stopping and idling.

Highway mpg typically is the highest because uninterrupted driving tends to burn less fuel.

A good city mpg is between 14 to 22 mpg and a good highway mpg is between 30 to 45 mpg.

The actual mpg depends on the car as some cars get lower gas mileage than others.

Having a full gas tank does not get you any better gas mileage as that has nothing to do with how much gasoline the engine uses.

All the gas tank does is hold the fuel and the fuel pump in the fuel tank then delivers the gasoline to the engine.

Some things that can cause poor fuel mileage are bad spark plugs, bad ignition coils, bad timing belt, bad timing chain, clogged fuel injectors, bad fuel injectors, and much more.

But the fuel tank whether it's full or not will not give you better or worse fuel mileage.

When you can do so it's better and easier on your car and cars transmission to accelerate slowly.

Instead of immediately stepping on the gas pedal and getting up to speed it's better to slowly press the accelerator to get up to speed.

However in some cases such as a freeway you have no choice but to get up to speed and accelerate fast but when it's safe to do so then accelerate slower.

Highway driving is better for your car because it helps keep the battery charged up, keeps the fluids flowing through the engine and transmission and also helps to heat the engine up to operating temperature which helps to keep the engine oil from getting moisture in it.

This helps keep the engine lubricated and protects the engine as well.

Highway Driving is much better for your car and your cars engine as the engine gets up to operating temperature which helps to drive moisture away from the engine and also gets the fluids flowing through the engine and also the transmission.

Stop and go driving is worse for your car.

When you do a lot of stop and go driving then you also wear out the transmission faster such as an automatic transmission that has to constantly shift from a dead stop to a first and second gear to get your vehicle moving.

Highway driving is always best for your car and your cars engine.

When you do a lot of highway driving your engine can reach operating temperature which helps keep moisture out of the engine oil and also prevents sludge buildup.

When you do just city driving mostly then your engine will not get up to complete operating temperature to burn off the water that can be present in the oil and you get a lot more sludge buildup.

City driving mostly is the worst thing a car can have done to it when it comes to extending the lifespan of the engine.

All that stop and go driving is not good for the engine or transmission either.

You also wear your brake pads or brake shoes out faster when you have to press on the brakes often to stop which you do more of when you're doing city driving.

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