Q: Bad gas mileage

asked by on August 01, 2016

My truck has been getting low gas mileage lately. About a year ago, it was around 15 MPG and now it dropped to 8 MPG. I understand that it is a truck and needs a lot of gas, but this is very poor gas mileage. I've done some checkups and everything seems fine. The catalytic converter is ruled out as a cause. I had the intake cleaned; spark plugs replaced; wires checked; new air filter installed; switched to Shell gas. What could be causing such bad gas mileage?

Hello there. A decrease in fuel milage can be attributed to a few different faults. The most common causes are leaking fuel injectors, oxygen sensors, coolant temperature sensors, vacuum leaks or exhaust leaks. A qualified technician, such as one from YourMechanic, will check all of these for proper operation and can make any repairs required.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Does the engine need to be lifted forward in order to replace the oil pan gasket?

Hi there, thanks for writing in. The oil pan is clear to be removed without lifting the motor. The original pan gasket is riveted to the pan. The new gasket does not need to be riveted on to pan for...

Rough Idle in park and neutral runs smooth in gear

You will need to have the engine checked to see if you have codes to assist with diagnosis before looking at getting the ECM reprogrammed for the rough idle at a dealer. I would suggest having a certified technician diagnose...

Battery replaced, engine malfunction warning

Hello there. With any Check Engine Light, the first step is to have the code read to determine what system is involved with the fault. It is possible that this fault was caused by the vehicle losing power when the...

Car turns off after driving 20 miles

Hello there, a few different parts can cause the vehicle to stall out and die like you have described. The most likely are the fuel pumps, an intermittent wiring issue, a bad battery cable, a faulty EGR, vacuum leak or...

Car was saying low oil pressure then started making a loud noise then then it leaked all of its oil out

Hi Jerry. What you are describing is a rather clear indication of an oil line leak. There are multiple oil lines and connections that are near the upper portion of your vehicle, that can leak on the exhaust, so knowing...

Battery light was on and now car won't start and keys stuck in ignition

Hi there. It more than likely that you are experiencing an issue with the alternator or the main relay as opposed to the battery itself. Once your car starts, power to all components and accessories is provided by the alternator;...

Part banging against wheel well

Although I haven't seen it very often, broken springs can happen. The springs are usually made of hardened steel. They help stabilize the strut and keep the car at the appropriate ride height. If the spring breaks, the rear of...

Brakes, transmission, starter, & catalytic converter replaced, but not fixed

The exhaust would need to have been removed when the transmission was done and may have been installed back on incorrectly or is misaligned causing the popping noise. A popping noise is usually due to a leak in the exhaust...

Front exhaust pipe/check engine light

The flex pipe is a common repair on your car. Most shops just weld in a new one, or that section of pipe can be replaced as a whole. Almost every time I would see and hear the pipe leaking...

Related articles

A Buyer’s Guide to the 2012 GMC Yukon
When When you want a big SUV that can hold its own, come what may, you’ll be happiest with a GMC Yukon. Although the inside of one of these vehicles can sometimes resemble an upscale hotel room, the 2012 GMC...
Symptoms of a Bad or Failing Intake Manifold Runner Control
Common signs include difficulty starting the engine, the Check Engine Light coming on, engine misfires, and a decrease in power and acceleration.
How to Install a Catalytic Converter
A catalytic converter is one of the most important emissions components of the modern gasoline engine. It is...