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Improving Miles per gallon (mpg) on a Prius and other hybrids

There are many things you can do to improve your gas mileage particularly if it used to be higher.

First if the check engine light is on get an OBD2 (On Board Diagnostic) reader and read the codes. They will tell you a lot about what is wrong with the car. The OBD reader plugs into a large D shaped connector at the bottom of the dash near the driver's left knee. The cheaper ones are less then $35 and give you less information and you have to look on the Internet to understand the error codes.

  1. Cleaning engine: Prius 2007 with 295k miles but replaced engine with an engine that has around 100k miles on it. MPG went from 42 or 43 to 48 as indicated on the central dash.

    That is a 13% improvement in MPG!

    (The 48 Mpg is my normal short trip driving pattern on long trips I get 50 Mpg!)

    What did I do? I just added Sea form as indicted to the oil and gas and then drove 245 miles and had the oil changed. (See directions on the can.)

    But there another very important benefit! If you keep you piston rings clean the oil stays cleaner and you burn less oil. This means your engine and catalytic converter last longer, way longer! I have taken two Prius above 270k miles. One a 2001 Prius I scrapped because the Catalytic Converter needed to be replaced and it was too expensive to replace in California. The 2nd a 2007 Prius I had to replace the catalytic converter and the engine. (The picture above is the engine. A broken connecting rod tore out the side of the engine.) I am talking a lot of money you can save not to mention saving money on gas!

    If you are burning oil badly you can also do a 100% Sea Foam soak on the piston rings. I have a write up here with lots of pictures and data on hybrid piston rings.

  2. EV (electric vehicle) mode. In the first 5 minutes of a drive the engine will idle just to warm up. By using EV mode you running on battery only and the engine does not idle. Once you get up to 35 mph Ev mode will turn off automatically if you start to go up hill turn it off.. Now you are warming your engine but getting work out of it. You will no longer see lower mpg in the first 5 minutes of your trip and lots of small trips will not bring down your overall mpg very much. If the first part of your drive is down hill this can save you some gas!

    The US Prius 2004 to 2009 did not come with an EV switch. For more information go here.

  3. Spark plugs. They may last 100 thousand miles but if you clean and re-gap them more frequently you will get another mile or two out of a gallon of gas. And while you are looking at the spark plugs look at coloration of the deposits. There are lots of sites with pictures that explain this.

  4. Air Filter just look at it. If it is dirty. Clean or replace it.
  5. Other general maintenance items. A site with lots of pictures for a Prius 2004 (2001 to 2009 and Prius C have the same gasoline engine) is here

  6. Driving habits: This is a huge subject but if you are racing up to red lights or are constantly heavily accelerating and braking you might want to change your habits. (Start slowing down as soon as you see a red light, if you time it right you will get through faster with a lot less fuel burned.) The gas consumption data on the Prius should help you.

  7. Tires: Put as much pressure in your tires as you are willing to and use low rolling resistant tires.

  8. Engine oil: It is easy to examine the condition of the oil by looking at the dip stick. Synthetic oil or oil additives will give you a few more miles per gallon less engine wear and longer engine life.

  9. engine air filter: Replace or clean if dirty. On the Prius there are three snap on and snap off clamps that hold down the top of the filter assembly it is very easy to access.

  10. Clean the airflow sensor. On a 2009 and earlier Prius it is a little square box with two Phillips screws. Directly below the air filter toward the front of the car. You can clean this with rubbing alcohol (found right in your bathroom) pouring it in and shaking it around. I also use a Q tip but if you do make sure you do not leave any cotton. You should also check the throttle body while you are at it. It is just below the air filter and can be access by taking off the air filter housing.

  11. Check spark plugs. If it has been over 100,000 miles replace them or clean and regap. They are right at the top of the engine and they are easy to access and replace; if you have a Spark Plug socket (on a Prius a 5/8 inch plug socket works) and 10mm socket for the bolt that holds down the ignition coils. On the Prius you do not even have to disconnect the wires to the coils and the wires are just long enough that you cannot insert them in the wrong cylinder. Inspecting the condition of the spark plugs tells you a lot about the condition of the engine. They should be light grey and not oily. The insulation around the center electrode should have some white. (There are internet pages with lots of pictures on reading spark plugs.) The gap will have widen after a long service life you can clean and re-gap or replace.

  12. Upstream Oxygen Sensor. The data from this sensor is used by the Engine Control Unit to regulate the fuel air mixture. If it is not working properly it can cause a 10 mile or more drop in MPG and generate OBD misfire trouble codes. Before it gets to this point, it can still lower you mileage. Unfortunately this is not easy to replace. You can monitor the voltage output of the sensor with the more expensive OBD readers. I believe my sensors started to fail at around 120,000 miles in my 2001 Prius. The upstream sensor used in the 2004 + are very different and may last longer.

    To replace the oxygen sensor in a Prius you need to remove the wiper assembly which is time-consuming but not particularly hard to do.

    The oxygen sensor is inserted in the top of the exhaust manifold just back of the fire wall. There is very little space to get at it and it is often seized in the exhaust manifold. If it is seized and you are using the correct wrench or socket and some penetrating oil and cannot loosen it do not waste a lot of time trying. (I have spent hours and all I accomplished was a rounded sensor!) Jack the car up and remove the manifold cut off the sensor just above the manifold. A small cylinder should fall out of the sensor making it easy to line up the drill but use a drill press and a vice to hold the manifold still. Use bigger and bigger drill bits till most of the sensor is out and then re-tap. The exhaust gaskets in a Prius are very high quality and I have reused them.

  13. 12 volt battery: Since on a Prius the 12 volt battery does not have to crank the engine (the high-voltage battery does, it just powers up the computers, lights etc.) it can degrade to the point where it lowers gas mileage and yet the car can still start.

    On a Prius you can check it easily right from the center console:

    For a 2001 to 2003 Prius go to http://www.elearnaid.com/opbaandkitfo.html#test

    For a 2004 + go to http://www.elearnaid.com/12vo1topraub.html#test

    There can be many other things that will lower your mileage but the above list is some of the more common ones. All conditions will eventually deteriorate to the point where you get an error code and then the source of the low mileage can be easier to find.

Hybrid partsHybrid partsAs an owner of a Prius I have found some parts that you might want.(see below)

I have tested them on the five Prius cars I have owned. We have been selling 12 volt batteries for hybrids since 2005. The Optima deep discharge batteries work great on a hybrid. (These batteries have thicker lead plates to allow more discharges instead of lot of cranking amps. You do not need cranking amps on a hybrid because the high voltage battery cranks the engine.)

I have also been testing the Intimidator Prius Batteryand found it still had over 70% of capacity despite the fact that is was deeply discharged on several ocassions due to the car not being driven.

"A short time ago I sent an email requesting the USPS tracking number. I am now pleased to inform you that this information is no longer necessary, in light of the fact that USPS has already delivered my Prius battery. In my opinion this is nothing short of miraculous! Kudos to you and your shipper, the U.S. Postal Service!

The battery was very thoughtfully protected within the Priority Mail box, by the way. Thanks for your expert assistance!

Sincerely, J. H., Clarksburg, MD

P.S. I ordered this same battery about a week ago, from Amazon, whose Marketplace at that time was defaulting to a competitor of yours. Four days later, I received word from them that the battery was not actually in stock at their warehouse, but would arrive sometime within the next two weeks. When I pointed out that their online inventory through Amazon Marketplace had indicated that it was in stock at the time of my order, and that it seemed like they could have informed me otherwise in something less than four days, they got quite a bit "huffy" about it (putting it mildly). Anyway, more to the point, in less time than it took them to tell me that their own inventory control was deficient, you actually put a brand new battery in my hands, and shipped it all the way across the nation to get it here. I won't forget it!

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