Toyota Prius Hybrid - Experiance from a user, Part 2

Part 1 of this was something I just casually wrote in the hope of it will be of some use for few. Turns out there were lot of readers than I anticipated! May be it will not be a bad idea to share some of more detailed stuff too... Things I didn't put in the first post since I wasn't sure about the level of interest on technical details of a  Prius.

Tires : My model came with the most uncommon type of 165/65/15 low resistance. This was the type recommended for 1997 model Prius. Since fuel consumption statistics, mileage meter all must be depending on the tire radius size, all the statistics the car indicates to us could go wrong if we change the tire radius. However, using a different tire radius is not possible without changing Rims so I guess this is not a common scenario. However, tire inflation level is! Fuel consumption difference between using properly inflated tires and poorly inflated ones can be noticeable! When the tire is deflated, the length it covers per a single rotation is less, hence more rotations will be needed to cover a unit distance, resulting in high fuel consumption.

Surprisingly, 1997 model recommended tire pressures to be at a staggering 42 psi. Normally in Sri Lankan roads we use a pressure level of 28-32, most people preferring 30. in 1997 Prius, front wheels needed to be pressurized at 44 while the lower once were expected to be at 42. Difference was to offset the additional weight of the front area. Now, I infact tried those! want to know what happened ? Well, I got amazing fuel economy for a while and then I had to replace shock absorbers! Understandably, I haven't tried it since then. This setting is certainly not for non carpeted roads of Sri Lanka. Then again, we have much better roads now compared to 5 years earlier and if you are one of those lucky ones who can use a carpeted road all the time, then you should definitely give this a try. Inflating tires is a well known strategy to conserve fuel, something which was even suggested to all Americans by Obama himself!

Breaking : Because of the electric breaking in Prius, it is expected that one do not need to replace break pads that often. Can some one give us some statistics on this for a normal car? in my usage of the car for 6 years (close to 100,000 km)  I had to replace break pads just once. Like mentioned in the previous post, most of Prius parts are compatible with other Toyota models, and Toyota parts are not so expensive either so this was not something to boast about really. On the other hand, regenerative breaking is saving much more in fuel than saving on break pads. Statistics say that if you use it properly regenerative breaking can save up to 17% of the kinetic energy which will otherwise go totally wasted. Here, 'properly' means that to get the full benefit of regenerative breaking, we need to apply breaking smoothly. A gradual slow down of the car over a distance where we can clearly hear the humming noise of breaking. A sudden break will not be turning much of kinetic energy into electrical energy. (but it will save lives in an emergency! so do apply breaks with full force when you have to...)

Fuel economy hints :
This fact has been mentioned before but let me go through it again as this is the single most, biggest reason behind fuel wastage, even on a hybrid!

Trying to speed up (accelerate) when that is not really needed or meaningful.

How many times we see someone overtaking us, but then we catching up to them after driving normally while they are waiting at a color light! That is insane driving, we get no benefit at all by accelerating and be the first to reach a particular color light! If we know there is a stop in front, best and most sensible thing to do would be to stop accelerating and allow the vehicle to slow down, we could time this to perfection so that the vehicle stops at the exact spot is should be stopping. Doing that is much fun too! On highway, the strategy should be to drive in a comfortable constant speed (around 30-70) by tapping the accelerator lightly. Display should tell us when we are doing well in fuel economy. (instance bar hovering around 30 km/l) It is those occasions that we should try to lengthen. All these help us concentrate more on our driving and speed, which make us good safe drivers. Some of US states have actually reduced insurance amounts for Prius noting that Prius drivers get involved in far less amounts of accidents than the others. I guess this applies to other hybrid drivers as well. Being sensitive to fuel economy and be attentive to driving both go hand in hand.

As mentioned in the last post, a one cool feature of Prius is that the engine can automatically stop when the vehicle is idle (like waiting in traffic). This saves lot of fuel in city driving. However, this also means that the engine get auto started when we eventually start to move. (initially the vehicle goes solely on battery and then switch into petrol) When the engine get stops and started again frequently like this, it will put up a higher burden on the normal 12V car battery. If the Prius has to perform well, this 12V battery also need to be in good shape. Needless to say, power steering also is on electric so the stress on this battery is really high. This is one lesson I learnt after going through some hassle. It is natural to pay more attention to the bigger costly battery and forget about the little one. So make sure you keep a good eye on the little 12V fella as well!

One caveat in auto stop and start of the engine is that it works as expected mostly only when the AC is not running! reason ? In older models of the Prius (such as my one), AC gets the power from petrol engine like in any other normal car, so if the AC has to work, you need the engine running. In this case, sometimes even if your vehicle is idle, petrol engine will keep running. Turning AC off when the car is at a stop is not always possible in hot days. However, in recent models (after 2003 I guess) Toyota has improves on this by making AC also to run on battery! So the owners of newer models... let us know whether petrol engine totally stops at  traffic (while AC is fully on)

Looking at the fuel efficiency more on the LCD display is a great way of adjusting our driving. In a display like the image above, rightmost bar is our instance performance that is how many km/l or miles/gallon are we doing RIGHT NOW. Other 6 bars are average fuel consumption in last 30 minutes divided into 5 minute periods. One thing you will see most of the time is that the average efficiency in the first 5 minutes of the journey is usually low. Reason for this is that the petrol engine (of any vehicle) needs to get heated up to a optimal temperature to perform well. Until it reaches that point it can't maximum efficiency. This means if the usual drive is about 20-25 minutes or shorter, then the overall fuel efficiency suffers noticeably due to the first 5 minute issue. In later models Toyota engineers have come up with an ingenious solution to improve on this. They have introduced a vacuum flask which will keep all the heated air when the engine stops and use that when the engine get started next time. This reduces the need to heat the engine all the time. Just a one example how far designers have gone to provide the maximum mileage for each drop of fuel..  

What about things which can go wrong... (As Murphy's laws predict, "If something can go wrong, it will - at the most inappropriate moment") I have some experiences to share on these issues as well. Will try to share them with you in another post. Meanwhile, feel free to send in any questions and your own experiences, those will be most welcome!

Happy, Safe, Clean and Economical Driving!