Skip the auto shop - Our mechanics make house calls

Q: How full should I keep my gas tank?

asked by on

How full should I keep my gas tank?

In my opinion, you should keep your tank at least half full at all times. This is not for any mechanical reasons but more for personal safety reasons. If you treat the halfway mark as if that were the empty mark, then when an unforeseen event happens you will have a cushion of fuel. Emergencies happen without warning and the security this provides will bring peace of mind. In foul weather you could become stranded on the highway and run out of fuel. In extreme weather this can pose a threat to your health. A fuel or gas gauge is not exact and cannot guarantee how many miles are actually left until the tank is empty. Some people think that there are still many more miles left once the gauge is at E, while others swear that once the Low Level Light is on, if they don’t get fuel they may run out before they get to the next station. A vehicle breaking down cannot usually be avoided since parts can break or fail without warning, but you can avoid damage or the inconvenience of running out of fuel if you simply keep the tank filled.

From a mechanical point of view, modern vehicles have evaporative emissions systems to prevent fuel vapor leaks from the tank. In order to test these systems, criteria need to be met before the test can be performed. Many of these systems have temperature and level requirements in order to run the self diagnostic check of the system. You may have heard someone complain that the Check Engine Light came on in their car after getting gas due to a loose cap. This emissions monitor system generally requires the tank to be anywhere between 15 to 80 percent full in order to run the self diagnosis test properly. If the tank is constantly topped off or left empty, these tests may fail to run. For your convenience, safety and for the onboard monitor systems, keep your tank full.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. How full should I keep my gas tank?

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

Get a quote

What others are asking

Q: What does the fuel gauge show?

The fuel gauge is located on the instrument panel, and tells you how full your fuel tank is. The gauge has an F (Full) on one end, and an E (Empty) on the other. Where the hand points to lets...

Q: Advice on how to keep cars that aren't used very often from rotting

Yes, it depends on how long the car is going to be sitting. Your tires could possibly go bad. A lot of weight is sitting on the tires. It's a good idea to once in a while jack up the...

Q: Engine chokes after fueling

Hello. It is possible that you have a problem with the charcoal canister, but it sounds more like you have a problem with other parts of the EVAP system itself. The EVAP system helps control the emission system for your...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...