2001 Prius with deteriorating gas mileage - a good mechanic in MD/DC

[Krolik]

Hello,

I am a new member but have been reading this site for a while and have found much that is useful. I really hope you can help me.

Four months ago I bought a 2001 Prius with 133,000 miles. The previous owner was getting high 40s - low 50s gas mileage on it. In the first few weeks of owning it, without using any special tricks, I got low to mid 40s. But then it started to deteriorate even as my driving style improved. Now I have read all about short trips and cold weather so let me make this absolutely clear, I am using long, smooth trips (two hours on an un-hilly un-congested highway holding steady at 65-70 mph) as a benchmark here. At the beginning I would get 47 mpg on a trip like that, now I am getting 36 if I am lucky. I recently tried inflating the tires - all were around 30-32, I pumped them up to 40. It had no effect.

Two things I noticed that may be important.
1)
When looking at the "Energy" monitor during these long smooth trips, I notice that most of the time there is a green arrow going to the battery. Sometimes for a second or so there is a red arrow going from th elelectric motor to the wheel but then it goes back. Could this mean the battery is not holding the charge so it keeps charging it?

2)
I seem to remember when the previous owner started the car the display light would come on but the engine would be silent. Then as she started driving and reached a certain speed, you would hear the engine come on. Now when I turn the key in the ignition there are two positions. In the first position, the light is on and the car is silent and there is also a check engine light that comes on. If I try to drive the car in this position it does not go. If I turn the key to the second position, the engine revs up immediately and the check engine and all other warning lights are off.

I'd like to take it to a mechanic but don't have anyone to ask for a recommendation (other than you guys) and looking online there isn't a single Toyota mechanic in the area with even halfway decent reviews. Also if I do take it to a mechanic I'd like to be able to sound a little less clueless than I am probably sounding right now. I do not claim to know much about cars but I am capable of answering simple questions (phrased with my ignorance in mind) I also have all of the previous owner's service records.

Thanks in advance to anyone who responds.

[Krolik]

Two other things I did not mention that are probably not related but I would be grateful for some advice on these as well.

1)
The "low coolant temperature" (blue) warning light has been on a lot lately, both in hot weather and in cold. The manual says to take the car in for service if that happens. But what exactly does it mean, in layman's terms. What could be wrong with it?

2)
Whenever I leave the car out in the rain, I notice that the carpet on the front passenger size is soaked. The driver side carpet stays dry. There are no visible holes. I don't know what to make of this.

Thanks again for reading.

[john1701a]

That blue light is not a warning. It is a warmup indicator, which will always illuminate for the first few minutes of travel.

As for the arrow/battery behavior, topping off a majority of the time with only a quick draw is what I remember on the highway with my 2001.

Turning the key to the second position is how you start the system for driving. The engine will always run. There is no straight-to-electric available, though the engine will shut off mighty quick if it's already warm.

In other words, the sudden MPG drop is likely a non-hybrid issue. A clogged air-intake (check the filter) will definitely influence in a bad way. The recent switch to winter-formula fuel along with colder temperatures and oil-overfill are likely contributors too.

.

[Krolik]

Thanks, John!

How do I check the air filter?

Also, the coolant indicator seems to be on for more than just the first few minutes of driving. Should I be concerned?

[john1701a]

Originally Posted by Krolik

How do I check the air filter?

See pages 29-30 of the User-Guide.

.

Originally Posted by Krolik

Also, the coolant indicator seems to be on for more than just the first few minutes of driving. Should I be concerned?

It seemed like forever before mine shut off in Minnesota during the winter. Blocking the grille and/or using a engine-block heater will reduce warm-up time.

If you want to know more about what goes on in Prius, consider getting a ScanGuage. You can see the actual coolant temperature then. I watch for 145°F, which is when the engine will shut off.

.

[Krolik]

Thank you, John.

I think I have managed to narrow it down. I noticed that the mileage goes way down when the air conditioning is on.

I keep the AC on a lot, usually setting the fan speed to auto and the temperature high in the summer and low in the winter but using fresh air not recirculated. So I know some of the good mileage I achieved in the past was with the AC on. But at some point something bad must have happened to the AC.

Yesterday I let the car idle with the AC on. Normally the engine turns off after a couple seconds of idling, with the AC on in the past it might have taken a few seconds longer. But yesterday it was on for 7 (!) minutes until I finally turned off the AC.

Today I kept it off for the entire day and got my best mileage yet - 47 mpg on my daily commute (10 miles to work and 10 miles back, under less than ideal traffic conditions)

In your experience, what is normal as far as the effect of the AC on gas mileage?

In other things, monitored that blue light today, it does go off after a few minutes (with the AC off). And still don't know what to make of the puddle in front of the passenger seat.

[john1701a]

Originally Posted by Krolik

In your experience, what is normal as far as the effect of the AC on gas mileage?

Well... it was... quite bit. In fact, that was a major benefit from my 2001 to 2004 upgrade. With the older model, the cooling system depended entirely on the engine running. With the newer model, it's electric... allowing the engine to remain off significantly more.

.

[blazer_5154]

Originally Posted by Krolik

Two other things I did not mention that are probably not related but I would be grateful for some advice on these as well.

1)
The "low coolant temperature" (blue) warning light has been on a lot lately, both in hot weather and in cold. The manual says to take the car in for service if that happens. But what exactly does it mean, in layman's terms. What could be wrong with it?

2)
Whenever I leave the car out in the rain, I notice that the carpet on the front passenger size is soaked. The driver side carpet stays dry. There are no visible holes. I don't know what to make of this.

Thanks again for reading.

Are you sure that the puddle in the passenger floor is water? Do you notice a sweet smell inside the car? I have had an older car (not prius) develop a crack in the heater core, which is usually located deep inside the dash on the passenger side of the car, through which the engine coolant proceeded to leak, filling the floorboard on the passenger side. Some vehicles register the coolant temp. from the liquid itself, meaning that if there is no coolant, the temp. will register low. If this is the case with your car, you will want to have the heater core replaced immediately, before you end up running the engine dry.

[Rokeby]

Originally Posted by blazer_5154

Are you sure that the puddle in the passenger floor is water? ...

Along similar lines, I wonder if the liquid could be coming from an overflow
from a blocked in-cabin heater-A/C condensate drain.

[bwilson4web]

Hi,

The fresh air intake is on the passenger side and air filter located behind the glove box. If you can, there are one or two plastic pins that slide in and allows you to lower the box and get it out of the way. Behind the box is the fresh air filter. Remove it and look for evidence of water and also how full of 'stuff' it is. Replacing the filter is fairly straight forward. If there is no evidence of water on the filter from outside, it suggests AC condensation water and a blocked drain.

You need to minimize use of "defrost" because it runs the AC constantly to dehumidify the air. This is good for windows but bad for mileage. Also, Max AC is solidly on whereas the normal AC control is thermostat drive.

I cut through my neighborhood an extra mile in the morning to keep my speed at or under 25 mph while the engine warms up. During warm-up the engine is inefficient but later the car becomes much more efficient.

There are a few critical speeds that help you improve mileage:

• 38 mph and lower - lets the car alternate between engine running and electric mode. This range is the most efficient.
• 55-65 mph - are excellent cruise speeds for high efficiency. It begins to fall off above 65 mph, 52 MPG goes to 49 MPG, and at 75 mph it drops to 39 MPG. Really see 65 mph as your best cruise speed and 55 mph as your best hill climb speed (keeps the engine in an efficient range.)

Of course the usual things apply:

• highest pressure in tires that you feel comfortable with
• oil between the "F" and "E", never over "F" mark (oil change should never add more than 3.5 quarts!)

GOOD LUCK!

Bob Wilson

ps. My MPG vs MPH chart for NHW11: