Drop in performance / mpg? Going to dealer, please help!

First, the "Check Engine" light only comes on if something in the car throws a code (i.e. if something is wrong). HOWEVER, it's worth saying that the "Maintenance Required" light DOES come on every 5000 miles, or so. So, if you're sure you actually saw the "Check Engine" light, then you should probably get it checked out at the dealer.

A few things to think about for why you may be getting reduced mileage:

1. Tire pressure. When you got new tires, did the shop set the pressure to an appropriate level?

2. The tires, in general. While people are often unhappy with the "stock" Prius tires (the GY Integrities), one thing they do have going for them is that they are low rolling resistance, which leads to fairly good mileage on them. If you had the tires replaced with something else, that may explain it. Some people also say that there's a "break in" period for tires and you don't get your best mileage until you've gone a couple thousand miles on them.

3. Oil overfill. Did you get an oil change at the same time you replaced the tires? Is it possible that the mechanic overfilled the oil? That's been known to negatively impact the mileage.

 

Maybe AC is running harder last few months ? I got my best fuel efficiency ever Friday morning (3.7L/100 KM), but got only 4.4L/100KM, about 18% drop on Friday evening with the AC running. My 20 mile commute that seems to be roughly equivalent in each direction.

 

I'm seeing a troubling hot weather battery related low MPG complaint trend here. 3 different threads started in the last few days:

sudden battery discharge

rapid HV battery drain on startup hot days only

Drop in performance / mpg? Going to dealer, please help!

I'm thinking this could be a widespread "defect" in Gen-II Prii...

 

Observation is not causation. Wait until next fall when you will see an avalanche of Why did my milage drop? when the weather turns cold.

 

Ah. Excellent. So, don't worry about that. It's basically just a counter that tries to remind you that you should probably get an oil change. Definitely do check the tire pressure out. It can make a huge difference (5-10 MPG in extreme circumstances).

So, did you replace the original tires (Goodyear Integrities) with new versions of that same type of tire. If not, did you replace them with other "low rolling resistance" tires? That can also make a huge difference.

This is a great point. A/C can have a big effect on mileage.

Perhaps your drop in MPG is just a combination of:
1. new tires,
2. running the A/C more
3. low tire pressure

#1 is something that you're probably not going to do anything about (although you could consider lower rolling resistance tires for your NEXT set of tires. As far as #2, you should decide how important it is to be in an A/C-ed car compared to getting good mileage. As far as I'm concerned, A/C is the best invention of the 20th century and you can pry it from my pleasantly cooled, dead hands. #3 is something that you should definitely take a look at; low tire pressure can affect not only your mileage, but your safety, too. Under-inflated tires can be just as dangerous as over-inflated tires.

 

With the recent hot weather in NE, I have noted that when the AC is on Max fan, the MPG drops to 40 mpg or lower. Going to med or low on the fan seems to frive the MPG on the same route to 45-50 mpg - this has been noted elsewhere but just keeping the fan on med will help significantly with mileage and I think the battery situation.

 

Re: Drop in mpg? Before: 50-55mpg. Now: 40-45 Going to dealer..any advice?

I would not suggest to go to a dealer and have your car check. If you do not see your CHECK ENGINE LIGHT is on then do not go there.
First let me ask you some questions.

1. Did you have your oil change? (5W-40 Fully synthentic oil is what you need change)
2. Did you check your air filter? (clean it or replace it)
3. Did you set all tires to 45 PSI?

MY USEFUL TIPS (FOLLOW THESE TIPS BEFORE GOING TO A DEALER)

THESE ARE MY DRIVING TIPS AND I AWAYS KEEP MY EYE TO IT :
1. SET ALL TIRES TO 45 PSI
2. SET AC TO LOW AND ABOVE 72 FF (OFF YOUR AC MIGHT HELP YOU A LOT AS WELL)
3. ALWAY FILL HALF A TANK OF GAS
4. CLEAN YOUR AIR FILTER BY AIR BLOW IF YOU PLAN TO GO ON A LONG TRIP (REPLACE IT IF IT GETS DIRTY)
5. GO BETWEEN 60-69 MPH ( I ONLY DRIVE ABOUT 65 THE MOST SO THAT'S WHAT I GOT MORE MPG)
6. RELEASE GAS PENAL WHENEVER YOU SEE A SLOW TRAFFIC IN FRONT OF YOU ( I SAVE ALOT OF GAS ON THIS # 6 TIP)

* SOME OF PRIUS OWNERS MIGHT FIND THESE TIPS USEFUL AND SOME ARE NOT. SO I AM JUST GIVING MY TIPS TO YOU GUYS AND JUST WANT EVERY BODY TO SAVE MORE MONEY ON GAS.
IF YOU DON'T THINK IT IS USEFUL THEN PLEASE IGNORE IT.




GOOD LUCK EVERYONE !!

 

No, they aren't low rolling resistance. They are completely middle of the pack.

 

Re: Drop in mpg? Before: 50-55mpg. Now: 40-45 Going to dealer..any advice?

Front tires are supposed to be 2 psi higher than rear tires.

 

I had the same problem and was told to increase the air pressure in the tires. It worked. Just add 7 lbs per tire or have 42 or 43 lbs per tire. Ride is rougher but you will notice an increase in gas mileage. I drive almost exclusively on the highway and have over 100k on the car. Even with the increased pressure, I'm getting around 45,000 miles on a set of tires.

When you have your tires rotated, you've got to tell them not to mess with your air pressure or increase your pressure immediately after your tires are rotated. Car will also have better mileage in hot weather.

 

Is this what most have found to be true? Turning the ac from max to low or 72 makes that big a difference in FE? From 40-42 up to @50 with ac turned down??

 

As stated on my other thread"40 mpg at 67?", my mileage is substandard. I have been P&Ging all day. Pulsing to 39 and gliding to 33. My mileage is at 52.7. A lot better than before, I admit it' a lot better than b4 but please remember... 33-39 P&Ging. With this much work it should be better. What do u think??

 

i own a gen II (2206) Prius that i purchased in april 2006. i have been maintaining an excel file for two measures of fuel efficiency (1 -- based on the MFD (display) value per tank of fuel purchased, and 2 --- the cumulative efficiency calculated by the amount of fuel purchased and the number of miles driven since the previous purchase of fuel). i have a plot of lifetime gas efficiency (lifetime meaning since purchasing the vehicle and weighting the value by the amount of fuel purchased and miles driven).

two patterns emerge (regardless of MFD or gas purchased method) -

1) seasonal -- better efficiency during warmer seasons,

and

2) long-term -- imposed over the seasonal oscillation is a long-term (lifetime) decline in fuel efficiency.

someone said in this string that perhaps there is a problem with the gen II priuses in some way? i am wondering the same thing, but don't have any guesses about possible reason(s) why? oil and filter have been changed every 3-4 K miles, tires have been rotated every 10 K miles. air pressure in tires has been monitored and maintained at 42/40 psi. the decline in efficiency clearly is not related to tire purchase, etc. as the decline is steady since purchasing the car and punctuated only by small increases during warmer seasons.

also wondering why this pattern is occurring?

rags

 

I only have 5k on my 08. I' settle for good mpg now.

 

Please do not follow this persons recommendation to set your tires to 45 PSI unless the tire specifically states this is the recommended tire pressure. Over inflating the tires can cause you to get into an accident that could have been prevented.

You can gain mpg by overinflating the tires with more pressure in them then required, but they will have less surface area on the ground. This can cause poor steering and loss of control, particularly in wet conditions.

The recommended tire pressure for the 2008 Touring models with 16" tires are 35 psi front and 33 psi rear.

 

see what you get driving normal without P&G. I never pulse and Glide I just drive normal. If I take back roads and don't pay attention to the MFD I will usually be in the 60's. Like I said before its the wife and the constant short trips she sends me on that kill me.

 

My lifetime fuel economy continues to increase. I attribute this to "better driving", higher tp (set it wherever you want), more favorable weather, and the retained heat from the grill block. If you want to do better install the block heater.

 

Block heater?? In Florida???