Why is My Prius Gas Mileage Deceasing? Real Reason for MPG Drop

There are many posts on forums from users stating different reasons for the drop in mileage for the Prius. It was supposed to receive 49 miles to the gallon of gas in the city.  Many customers were complaining that their average in the city had dropped to 44 mpg.  It was a large drop, and numerous owners noticed it.

Toyota owner in California reported that customers were getting less mileage and that the inverters seemed to be causing the drop.

Why is my Prius gas mileage decreasing? Your Prius gas mileage could be decreasing because you had received the software upgrade that controls the functioning of the inverter.  The upgrade seemed to change the amount of power that was being sent to the transmission. This caused a higher reliance on the four-cylinder gas engine than before which decreased the mileage. Many owners reported their city MPG at 44, whereas Prius stated that it should be 49.

The decrease to 44 does not sound like a huge amount on the surface, but it not what was stated.  In 2010, the Prius has a rating of 51 mpg for city driving and it had a rating of 49 mpg in 2014.  That difference is minor, but down to 44 is very suspicious.

There were actually two claimants in Los Angeles that argue that the decrease was never announced to owners.  It was in a sense fraudulent and perhaps a total breach of contract.

Initially, Priuses were recalled to fix an overheating problem that could be solved by a software change.  The high temperatures were endangering the inverter.  The strange thing is that the fix did not correct the problem and is caused power to be lost at the same time. The loss in power was not happening before the fix.

The loss in power that increased the need for gas was evident to many after they had made the calculations.  Although, some owners are claiming that the change in the functioning of the inverter altered greatly the way that their Prius was functioning.  One owner stated that she had been driving in the fast lane and the car slowed down to 15 mph which actually put her life in danger.

Is a sudden drop in MPG a sign that other owners may experience a sudden drop in power on the highway? Scary thought.

Why is there a sudden drop in MPG for my Prius?

If you have an older Prius, that is a chance that your drop in mpg is not related to the infamous software problem that caused recalled calls to use more gas.

Watch the following video that explains why a Prius owner’s mpg was cut in half:

Here are a few situations that can cause an increase in gas usage for your Prius:

  1. Driving too fast on the highway could cause a difference in the mpg by at least 1 mile per hour.
  2. Using unleaded fuel all of the time has an effect on mpg.  There could be extra gunk that sticks to the engine.
  3. If you are running the air conditioner full blast, you are going to negatively affect your miles per gallon.  A hybrid car will switch over to the use of the gas engine if there is a large demand for power created by the air conditioner.
  4. Fuel economy can drop drastically during the winter months when compared to other times during the year.  People tend to use the heater, the heated seats, and the defrosting function fully at the beginning of a voyage during the winter.  The electric motor is not going to be strong enough to power all of these functions which means that gas is going to be used more.
  5. Good floor mats for your Prius are a plus. Click here to view the Husky Liners that available on Amazon.
  6. The tire pressure can be the culprit since low pressure will cause a reduction in the mpg and it can happen quickly if the pressure has dropped fast.  Low pressure also is not healthy for the life of your tires.
  7. Another component to verify is the 12v battery.  If it is the original one and you have had your Prius for a long period of time, the battery might be working as effectively as before.  This situation will cause more gas to be used.

How can I get better gas mileage in my Prius?

Getting better gas mileage is something that all Prius are interested in accomplishing. That is one of the main reasons why people invest in a hybrid car.

  1. Pick routes that allow you to travel at a speed of around 45 mph.  This will increase your mpg amount in your Prius.
  2. If you are traveling at more than 45 mph, try to coast in certain areas as much as better.  This will ensure that the electric motor is used to its fullest.
  3. Personally, I would not zoom away right away during the winter.  Give the car time to warm up slightly since a warmer battery will function better and also you will be using less fuel to warm up the interior of the car if you warm it up in a controlled manner.
  4. Make sure to inflate your tires to an amount that is 2 psi more than the amount that is stated in the manual.  Apparently, the manual has slightly lower amounts so that the ride will be smoother.
  5. As soon as you see a road sign indicating that you are approaching a stop sign, take your foot off of the gas and glide towards the stop sign.
  6. Make sure to use the cruise control and set it to below the speed limit on the highway.  It has been proven that you could lose as much as one mpg for each mph that you travel over 55 mph.
  7. Learn to activate regenerative braking as much as possible, this will save on gas which increases the mpg.
  8. Try not to use the brake as often when coming to a stop.  This will allow the regenerative braking to slow down the car which will charge the battery and reduce the dependency on gas.
  9. When accelerating after a complete stop, do so in a steady manner.  A steady increase in speed will use less power from the battery that commanding a sudden burst of power.
  10. Observe the ECO line on the dashboard, trying to maintain a speed that keeps the needle in that range will increase your mpg of fuel.
  11. During the winter, make sure that you warm up your Prius before leaving.  A warmer battery will increase your mpg since it will not require as much use of the gas engine.
  12. Do regular maintenance on your Prius.  This will allow the gas and the electric engine to operate better, which will decrease the mpg.

Besides getting lower mpg, perhaps you have noticed in the overall functioning of your Prius. What could be the problem?

Why does my Prius feel sluggish?

If you have had your Prius for long enough to drive it for 100k miles or more, you may notice that it starts to be really slow down and it seems to have to force itself to accelerate. You might be wondering if the electric motor is the problem or is it the gas motor that is causing this lack of energy feeling.

The electric motor has parts that do not wear as fast as the component in a gas motor.  The problem should be your gas motor, especially if you have noticed that change was gradual and not all of a sudden.  Nevertheless, it is time to do something about it.

Here are some tips to reduce the sluggishness of  your Prius:

  • Switch out the spark plugs.  This is going to increase the reaction time of the gas motor.
  • Change the type of oil that is being used.  Switch your car oil over to synthetic high mileage oil.
  • Get a new PCV valve.  The PCV value allows built-up gases in the crankshaft to exit.  If the gases build-up, there is the possibility that a gasket will blow.  If you wish to go the cheap route, just clean the sludge off of the valve.
  • As a Prius ages, the amount of change used to accelerate is reduced.   This will cause lower acceleration.  The HV is getting accessed more often.  The solution is to let an older Prius idle longer so that battery can warm-up.  You can keep the car in park while idling.  Idling for just a few minutes will be long enough.  Now you drive away without having to hammer the main battery for the first five minutes or so.
  • For your older model of Prius, get a new FOB cover case offered on Amazon by clicking here.
  • Another tip is just to be patient.  One owner of a 2004 Prius stated in 2016 that he had driven his Prius for over 250k miles.  He is satisfied at how long it has lasted.  He does notice that his Prius is sluggish, but he still has the original traction battery. His mileage is not what it used to be, but he tries not to overuse the airconditioning and attempts to help the speed relatively consistent.

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