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

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.

 

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.

 

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?

 

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.

 

blazer, Rokeby and bwilson4web, thank you for your advice. I did not check this forum for a few days but I did show the car to a mechanic and guess what, Rokeby was right, it is the cabin filter. So that explains the puddle and the air conditioning not performing as efficiently. Thank you everyone!