Better while cold??

Which car is getting 43mpg? If it is the 2003 does the battery's state of charge fluctuate rapidly?

If it is the 2006 best fuel economy occurs when coolant temp is over 170F as reported by my ScanGuage. For me the 1st 5 minutes is ~25mpg and the 2nd 5 minutes is ~50mpg. It takes about 15 miles (not sure how long) for me to recover what I lose at the start of the trip.

 

Let's start with the standard checklist:

• engine oil level - between the marks. If over "F", drain.
• engine oil quality - in the winter, 0W30 or 0W20 works
• wheel alignment - any metrics? Tire wear, even?
• tire pressure - as close to maximum sidewall as comfortable, +2 psi front.
• transaxle oil - has it been changed? I'm running Type WS (current generation oil) and it seems to be working fine. Even new Type T-IV is better than worn out, original oil.
• engine air filter - an annual change

The NHW11 (2001-03) Prius has a lot of efficiency challenges at temperatures under 60F. There are several things that can help:

• block heater - a half hour provides 25C boost, an hour comes closer to 30C and can save about a minute of warm-up
• neighborhood start - using the neighborhood streets, do the first 1-1.5 miles at 25 mph to let the engine warm up before putting a load on the engine.
• urban cruise - try to stay away from 42 mph, 0-38 mph and 45-65 mph works best as repeated transitions through 42 mph seems to lead to poorer performance.
• maximum cruise control - where travel is relatively flat, cruise control avoids 'nervous foot' that can run the engine up to inefficient RPM ranges. If you have a scanner that reports engine RPM, I try to keep it under 2,600 rpm in cruise and within reason, avoid engine rpms above 3,200 rpm.
• modest end - within 1-2 miles of trip end, try to run as close to 30 mph as practical so the battery can provide excellent ending MPG
• hill climb - absolutely avoid accelerating up a hill and try to climb at 55 mph if practical. Counter intuitive, a constant speed of 75-80 in a climb of a relatively small hill, ~500 ft., also works by using traction battery energy BUT this is not recommended and never accelerate up a hill to this speed as you'll use all of the traction battery energy accelerating and there won't be any for cruising up the hill.

I'm curious, how many miles on the 03 Prius? How long have you had it?

I'd also recommend recording your mileage to have a record and track mileage as a function of temperature and other variables. I started with the GreenHybrid.com mileage database but it has been replaced by MyHybridCar.com. There are others including the EPA http://www.fueleconomy.gov/ site. Regardless of how mileage is tracked, one of my earliest efforts was to plot MPH vs MPG:

It takes time, a couple of months, to build up a mileage record but it provides the facts and data to understand how our vehicles perform. With more sophisticated instrumentation, you can plot engine brake specific fuel consumption:

Of course this may be a little more detail than you were expecting.

Over a two month interval, I've found achieving the original EPA numbers, 45 Hwy and 52 City, was fairly easy. But it took careful study and route planning to achieve my current 52.2 MPG. Still, I live in Huntsville AL and have the advantage of relatively flat terrain but careful route planning pays dividends:


GOOD LUCK!
Bob Wilson

 

Sounds like it is due for a two-fer. Just use 3 quarts of an affordable, quality motor oil and new filter. You'll probably need a really serious oil filter wrench. IMHO, go with cheap, quality oil on this change. If the oil looks as bad as I think it will look, threat this first change as a flush. Then in another month or so, do it again with a quality oil and filter. Your engine will thank you for it.

When you change the transaxle oil, have a new gasket and drop the pan. Also, have a small, clean, dry water bottle to take a sample. If the oil looks like some of the stuff we've seen in the past, it can be pretty ugly. If you have a sample container, you have the option of getting it tested. If not ...

Huh? Did the thieves break it? Any photos?

The early 2001 came without a cruise control but the actual cruise control circuit is just a resistor network and switches connected to a single wire into the hybrid ECU. If you have an experimenter's mind, there are some clever approaches you might consider. Over in the YahooGroup "Prius Technical Stuff," you'll find some pretty skilled Prius hackers who can offer some help and insights.

Interesting! A 2003 with 12k miles in 2009. That was quite a score.

Seriously, the cruise control would be a fun project and we can also go over how to add basic instrumentation. A tachometer is one of the single best mileage instruments around and if integrated with a smart cruise control, you'll have a real honey. Then if we add a thermistor hack, you'll be set.

I didn't mention it before but you may also want to change the interior air filter. They can get a little 'funky.'

Chat at you later,
Bob Wilson

 

No problem on the thermistor hack as you're seeing my engineering notes ... all of the details.

How does it compare to driving in "B"?

The car will protect itself. The real challenge is trying accelerate while climbing will be 'disappointing.' Also, it seems to climb best as far a fuel economy and efficiency, at 55-60 mph. Over 60 mph, it has to draw on the battery that is a limited resource.

That sounds about right.

You'll have to ask. My car is well past any warranty service but the traction battery and inverter were under an 8 yr / 100,000 mile warranty. You may be OK on the battery work.

GOOD LUCK!
Bob Wilson

 

Thermistor hack

To the best of my knowledge, only three, NHW11 owners ever worked on their individual thermistor hacks:

• Clive (UK) - who originally proposed the idea using a resistor network, possibly a diode. I saw one posting this winter about it but no follow-up.
• Cor (now in India) - who reported building a 'transistorized' version but subsequently sold his NHW11 Prius and now is in India.
• Wilson (me) - who experimented first with a potentiometer; potentiometer and diode; and finally built the MSP430 version.

The 54,000 NHW11s benefit from the thermistor hack saving 3-6 minutes before going into hybrid mode. The ~500,000 NHW20 Prius use a thermos bottle and improved control laws that limit the utility from the thermistor hack. The new ZV30 uses an exhaust heat recovery system, which eliminates just about any need for a thermistor hack.

Another approach is to get a block heater installed. This can save about 2 minutes of warm-up but at 400 W., it should be plugged in about an hour before leaving ... 30 minutes is OK too. Many folks use a timer to turn it on early in the morning. These run about $50.

In the winter, I also use a radiator block, a 'water noodle' that is split and held in place with two bungie cords. It is the difference between getting 50 MPG down to 40F or only 45 MPG. It cost about $10.

If you are interested in a thermistor hack, we can work out what approach works best for you. There is not enough demand to justify 'mass production.' If you want one, I can build out another microprocessor version, test it and send it out, say $100.

NHW11 DRIVING STYLE

At 13 seconds to reach 60 mph, it is not a 'road rally' car. But if you can "zone out" while driving, it can be fuel efficient. The rules of thumb I follow:

• 1-2 miles - 25 mph to let the engine warm-up to hybrid temperatures, use a 'water noodle' to block the bumper air intake at temperatures under 70F.
• Steady speed, 0-38 mph, or 45-65 mph. When climbing, try to use 55 mph if safe or use a truck as a pacing vehicle. A heavily loaded, moving van drives nearly the perfect cross country speed ranges ... DO NOT TAILGATE ... just follow their driving style.
• Last 1-2 miles, use 30-35 mph to maximize EV mode.

But I have always been a 'Zen' driver who prefers to keep to the speed limit and drive in a calm state of mind. If you prefer to minimize driving time, you'll get there but often be frustrated by the NHW11. It won't perform quickly but it will burn up more gas.

However, with good tires and high inflation pressure, it will take a curve faster than about 80% of most vehicles. Experiment carefully but when I switch to my wife's Echo, I have to remind myself that it can not take turns like I do in my NHW11 Prius.

GOOD LUCK!

Bob Wilson

 

I am interested in thermistor hack