MPG Dropping

prius-yes-dubya-no · 08-31-2006, 09:02 AM

I bought my 2006 Prius in January of this year and was consistently getting 45 mpg on every tank of gas up until June of this year. Then I started noticing that my average MPG was dropping at first to about 40 and now for the past 2 months consistently around 37 mpg. I am doing the same amount of driving (basically to the same places and same combination of highway / non-highway driving). I'm trying to figure what is causing this, there are several factors I think might be suspect.

I have always bought the lower 87 octane gas for my car (usually from ExxonMobil) and I understand that gas is being mixed with more ethonol and I don't know if that is part of the problem. Does the octane make much difference in mileage that we are getting on a tank of gas. I don't like the idea of paying .25 more per gallon of gas to go from lowwer octane to the highest, but if paying this amount increases my MPG by 5 or miles, it would be worth the cost.

I live in the Dallas Texas areas and our temperatures since June have been very hot (typically upper 90's to over 100 degrees all summer). Are temperatures are warm enough most of the year to use the AC so it is generally running all the time when I drive, but with these higher temps, it is probably running harder. How much affect does the AC on the MPGs.

I have also noticed that when it is hotter outside, my car's battery seems to lose the charge while the car is sitting in the parking lot while I am at work. Does the heat have an affect on the battery maintaining a charge while the car is off? It seems like I can get out of the car in the morning with a battery charge of 6 bars and when I get in the car at the end of the day, there might be 3 bars. Is this normal?

I appreciate any insight people may want to share.

SomervillePrius · 08-31-2006, 09:07 AM

Having to use the AC def. drops the MPG quite a bit. I would also check your tire pressure as it has a direct impact on fuel efficieny.

The battery might "loose" a charge when cooling down. I notice that in my car if I park it with 4 bars in the evening then in the morning it might start-up with three bars. I think this is from the battery cooling down.

**efusco** · 08-31-2006, 09:28 AM

Make sure your air filter (the one under the hood) is clean/clear.
Make sure your tire pressures are at least up to the OEM rec levels and consider setting them a bit higher, many of us use 42f/40r
Check the oil level and make sure it wasn't seriously overfilled.

Do NOT switch to a higher octane fuel, that won't help. The amount of ethanlol in fuel may have a small negative impact on FE, but not a big one.

You're seeing your battery SOC drop almost certainly b/c of the heavy AC use...it causes a huge drain.

You didn't say what setting you're using with your AC. I recommend Auto A/C set at around 78 degrees. That will keep the cabin comfortable and minimize the AC use. It won't make it feel 'cool', but it won't be hot either. If you're not willing to adjust the temp to that level or so then you're going to see a greater and greater impact on FE the cooler you set it.

Do what you can to alter your commute route to take greatest advantage of your car. Longer runs at 35-45mph will be a big help, stop and go, esp. in the high heat, is a killer. Don't speed, allow for greater following distances and anticipate stops and such far ahead of time.

Read my article:
http://priuschat.com/index.php?autocom=art...howarticle&id=3

08-31-2006, 09:02 AM	#1
prius-yes-dubya-no Join Date: Oct 2005 Posts: 19 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I bought my 2006 Prius in January of this year and was consistently getting 45 mpg on every tank of gas up until June of this year. Then I started noticing that my average MPG was dropping at first to about 40 and now for the past 2 months consistently around 37 mpg. I am doing the same amount of driving (basically to the same places and same combination of highway / non-highway driving). I'm trying to figure what is causing this, there are several factors I think might be suspect. I have always bought the lower 87 octane gas for my car (usually from ExxonMobil) and I understand that gas is being mixed with more ethonol and I don't know if that is part of the problem. Does the octane make much difference in mileage that we are getting on a tank of gas. I don't like the idea of paying .25 more per gallon of gas to go from lowwer octane to the highest, but if paying this amount increases my MPG by 5 or miles, it would be worth the cost. I live in the Dallas Texas areas and our temperatures since June have been very hot (typically upper 90's to over 100 degrees all summer). Are temperatures are warm enough most of the year to use the AC so it is generally running all the time when I drive, but with these higher temps, it is probably running harder. How much affect does the AC on the MPGs. I have also noticed that when it is hotter outside, my car's battery seems to lose the charge while the car is sitting in the parking lot while I am at work. Does the heat have an affect on the battery maintaining a charge while the car is off? It seems like I can get out of the car in the morning with a battery charge of 6 bars and when I get in the car at the end of the day, there might be 3 bars. Is this normal? I appreciate any insight people may want to share. __________________ Paul 2006 Prius, Black, NW8 package, Tan Leather, Wood Grain Irving Texas

08-31-2006, 09:28 AM	#3
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,709 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 26	Make sure your air filter (the one under the hood) is clean/clear. Make sure your tire pressures are at least up to the OEM rec levels and consider setting them a bit higher, many of us use 42f/40r Check the oil level and make sure it wasn't seriously overfilled. Do NOT switch to a higher octane fuel, that won't help. The amount of ethanlol in fuel may have a small negative impact on FE, but not a big one. You're seeing your battery SOC drop almost certainly b/c of the heavy AC use...it causes a huge drain. You didn't say what setting you're using with your AC. I recommend Auto A/C set at around 78 degrees. That will keep the cabin comfortable and minimize the AC use. It won't make it feel 'cool', but it won't be hot either. If you're not willing to adjust the temp to that level or so then you're going to see a greater and greater impact on FE the cooler you set it. Do what you can to alter your commute route to take greatest advantage of your car. Longer runs at 35-45mph will be a big help, stop and go, esp. in the high heat, is a killer. Don't speed, allow for greater following distances and anticipate stops and such far ahead of time. Read my article: http://priuschat.com/index.php?autocom=art...howarticle&id=3 __________________ Evan E. Fusco, MD Seaside 04BC9/OEM EVb/NAV & auto-BT/XM Radio, CAN-View, Shark Fin, BT Stiff. Plate, Skid Plate & Strut Support

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08-31-2006, 09:07 AM	#2
SomervillePrius Senior Member Join Date: Jan 2006 Location: Somerville, MA Posts: 946 My Car: 2006 Prius Package: #9 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Having to use the AC def. drops the MPG quite a bit. I would also check your tire pressure as it has a direct impact on fuel efficieny. The battery might "loose" a charge when cooling down. I notice that in my car if I park it with 4 bars in the evening then in the morning it might start-up with three bars. I think this is from the battery cooling down.