Dropping MPG

Few questions:
1) are you changing your oil and rotating your tires regularly?
2) what pressure do you have your tires inflated to?
Few factoids:
a) in cooler weathers, the ICE (gas engine) stays on more to keep the emissions stuff hot so it can function properly - ppl stuff their front grills w/ pipe insulators to help keep the engine warm
b ) in cooler weathers, the ICE takes longer to warm up - installing an EBH (engine block heater) will help reduce that time.

<div class='quotetop'>QUOTE(EllenH @ Oct 1 2007, 05:31 PM) [snapback]520026[/snapback]</div>

 

Our 05 Prius has 75k and mileage hasn't changed at all. My question is...have you changed the engine air filter?

 

<div class='quotetop'>QUOTE(EllenH @ Oct 2 2007, 08:25 AM) [snapback]520239[/snapback]</div>

• tires and alignment
• transaxle oil change

 

I hit a personal all-time record of 59.1MPG over 59 miles in August, so age (and even a weakened wheel bearing) doesn't really impact a Prius that's been decently maintained.

Darn hills around here make these records only possible on road trips, though...

 

[As the car wasn't used much during the cold months, I pretty much ignored this. With spring I was hoping for better mpg.]

Could it be the Traction battery? The Prius needs to be driven regularly to keep the NiMH battery from discharging and aging prematurely. I believe the manual says to start it at least every two weeks.

 

Did the mileage drop after an oil change? If so, check the level. If it's overfilled you will definitely get an MPG hit.

 

drive it harder, it sounds to me like you drive like an old lady. The prius doesn't always like to be Babyied. It sounds to me that perhaps you are driving longer distances while moving the car with the battery and electric motors and that is significantly less efficient over more then just a short distance (1/4 mile or so) then using the engine.

 

Gratuitous insults don't help.

Ellenh, is the oil overfilled? Check it yourself now.

What tire pressures does it have? The most reliable way to check this is to buy a $5 digital gauge and do it yourself before you start the day's driving. (BTW, I don't rotate my tires regularly and it has no noticeable effect on fuel economy.)

If those two items are right, take it to another dealer. They're not all doofuses and by this time they should not have to learn from your car.

Fuel in large cities now contains ethanol most of (all?) the time, so the relatively new situation of E10 in cold weather may still be temporarily confusing the engine computer. If you just keep driving it as before you may get a pleasant surprise starting with the next fillup.

During cold months do you drive it less often or do you make shorter trips than at other times?

 

Have you changed your trip/commute length since the first year?

Have you started to use the heater more with cooler weather in the mornings?

Wayne

 

Hi Ellen,

All the stuff mentioned needs to be checked. Here is another one. Check out the rear brake temperature after doing a long trip. It should be about 100 F or less. If its significantly hotter, and/or one brake is much different in temperature than the other side of the car, you might have a stuck brake.

If you find a hot brake, have the mechanic take them apart, clean em up, and check the automatic adjuster.

When you operate the parking brake, make sure to lift your foot cleanly and completely off the pedal. If you think you did not get the pedal to come all the way up, reset the brake, and release it again.

The most probable causes are either the oil level/viscosity (10W40 is reported on PC here to cause the very symtoms) or the rear brake setting/adjustment.

Its not uncommon for cars that sit a month or two, to develop rust in the brakes, or brake adjusters.

 

Oil does not noticeably affect typical consumer automobiles' mpg at all. It's a myth that oil companies have propagated throughout the decades, in an attempt to sell more expensive synthetics.

The viscosity of oil in operating temperatures, even in pre-engine start operating temperatures, are never high enough to affect the power drain from the engine when compared to mechanical losses. Maybe with the relatively high rpms experienced by race cars, but not with regular consumer cars. The different viscosity oils do influence engine starting performance after very low temperatures overnight, but once started, within a couple of minutes, oils IS oils.

With age, the things you need to check in an ICE to maintain mpg ratings are:
1. fuel system degradation - gunk build up on manifolds, injectors... get a fuel system flush or try the injector cleaners available from gas stations
2. combustion system degradation - cylinder valves soot build up, piston rings wear, ignition timing re-calibration

Assuming the electric motor and battery systems are ok, I'd check the above first.

Obviously tires and tire pressures are easiest to check, but eliminating these, go for the above.

 

Hi Jimbo,

That may be true with other cars, but the wrong oil viscosity and an overfill in a Prius can even result in the car not starting the engine, and a bunch of codes. With the result that you have to be towed to the dealer. Check it out in older PriusChat threads. JiffyLube has been responsible for more than one stalled Prius on the side of the road.

This is why many of us change our own oil now. We know exactly how much to put in, and which oil to use.

Using 10W40 in a Prius, which is specified to use 5w30 will effect the mileage by the 10 to 20 percent the OP indicates, depending on how much of an overfill there is.

Overfills have two effects. Crank slap is possible, but rare. The more common cause is that the oil gets up into the intake manifold and effects something, probably the Mass Air Flow sensor (Hobbit probably can tell you specifically). This is probably due to the breathing action of the Miller head (which provides the Atkinson cycle action).

 

<div class='quotetop'>QUOTE(EllenH @ Oct 1 2007, 06:31 PM) [snapback]520026[/snapback]</div>

My miles took a hit this spring. I was getting 47 miles per gallon and it dropped to 35. I was going nuts trying to figure it out. I was driving the same as I always have. Then it hit me. I was buying Stewarts gas. I switched to a name brand gas and put injector cleaner in the tank and bingo my milage started to go back up. Now I am up to 48 to 50 mpg. Hope this helps you. My car is an 06 with less then 3,000 miles.

 

I've reformatted your answers to help list the know facts and data:
<div class='quotetop'>QUOTE(EllenH @ Oct 1 2007, 05:31 PM) [snapback]520026[/snapback]</div>

I have a 2003 Prius and my mileage continues to improve BUT I've made a study of older vehicles. There are a number of problems that can accumulate and a mechanic might miss. For a sudden drop, I would wonder if you have a higher formulation of ethanol in your gasoline. This is one potential source. In our area, Shell 87 has proved to be a high energy gasoline (also Exxon and Chevron but BP, Texaco, Conoco and Citgo tested lower) and one tank might be a good test.

LUBRICANTS

Just make sure the engine oil change was 5W-30 and it is not overfilled. Both wrong grade on a change and someone selling 5 quarts instead of 4 will overfill the engine case. Just pull the dip stick, wipe with a paper towel, and test to make sure the oil is not higher than the top fill mark, not even a little bit. Also verify they put in 5W-30 (I switch to 5W-20 in the winter) and a new filter on the oil change receipt. If it says 5 quarts, you are likely to have an overfill problem.

Although our long term testing says your model should go 50-60,000 miles before changing the transaxle oil, some folks are looking at earlier changes. There is no filter so overtime, stuff accumulates in the oil that can only be removed by changing the oil. But this is however unlikely at 28,000 miles.

ALIGNMENT

The rear axle of our Prius is especially difficult to align. When you had your tires last rotated, you should have gotten a print out of the the wheel alignment. It should also include the tread depth of each tire (or ask that it be included.) Given the difficulty and potential expense of a rear wheel alignment, while you are still under the 3/36,000 mile limit, you have a powerful argument for getting it done under warranty.

Even Toyota mechanics have a hard time when asked to do a rear wheel alignment. But some of us have been using shims to get the rear tires right on the numbers.

I understand the original tires tend to last a little over 30,000 miles. Based upon how much wear, you may need to consider shopping for low-rolling resistance tires with longer tread life than the original tires. The wear pattern will especially tell if the tires have been somewhat under inflated, the edges go first, or over inflated (less likely) with center wear.

INDUCTION AND FUEL SYSTEMS

Toyota has a kit that includes throttle plate cleaner, injector cleaner and even vacuum hose cleaner. The kit is about $20 and it would be a good idea to suggests this be done on the car . . . under warranty! This can avoid problems with a sticky throttle plate and other inefficiencies.

FILTERS

Make sure the engine air filter has been changed and the cabin air filter. The first helps the engine breath but more importantly, avoid dirt and dust contamination. The cabin filter helps the occupants. <grins>

WARM-UP

I've found that keeping the speeds below 25 mph for the first 1-2 miles or using an engine block heater significantly improves fuel economy. In my case, I cut through the neighborhood instead of heading for the cross town street. This 'rolling warm-up' does a great job of improving total trip mileage.

RECORDING MILEAGE

Using just a composition book or any of the web based systems, record your mileage on each fill-up. This will let you test different approaches, over weeks and months, to find out what works and doesn't work. This is the key to knowledge and insight, more than my other suggestions. Do this and you have the keys.

As for switching to another car, I can't answer that because it really depends upon your goals and objectives. For us, we run the cars 'until the wheels fall off' to minimize costs. But some folks prefer to have vehicles with the reliability and warranty protection of a new car. I can't help you with that decision. But if you are interested in selling your car, having some of the 3/36,000 warranty on the car should make it easier to sell.

Bob Wilson

 

EllenH,

Fill your tank up with a different brand of gas than you have been using. And do it when you have as little of your current gas still in you tank. Let it get down to that blinking bar if possible.

That just might do the trick.