This wolf in sheep’s clothing can show all of us a thing or two.
2001 - 2003 Toyota Prius-I - higher end FE techniques.
Wayne Gerdes - CleanMPG
- June 21, 2007
In terms of the 2001 - 2003 Prius-I’s Fuel Economy, she has near the same capabilities as that of her younger sibling, the Prius-II. With a less powerful overall system and less precise energy consumption mimic and SoC level, you only have to be a bit more cautious is all?
A Prius-I is quite capable of pegging all 30 minutes of the 5-minute bar consumption screen mimic while actually covering a decent distance but not without a very careful application of the accelerator under a relatively specific set of rules and driving on an almost completely unmolested roadway in terms of traffic and or road conditions. Just one impediment to a glide or having to EV a small hill causing your SoC to fall from full to half puts her 100 mpg + capability at risk. Although the Prius-I does not have the overall power, fuel economy capability or the ability to transition into and out of a given mode as seamlessly as her younger sibling, the Prius-II, she does have a key for FAS’ing to improve warm-up FE and a relatively large shift handle so as to place her in a pure Glide in Neutral when conditions allow … With the 100 mpg capability available, let us see what you can do under a variety of conditions to help improve your Prius-I’s fuel economy.
. As with any vehicle, higher tire pressure to reduce rolling resistance, higher quality and lighter weight synthetic oil to reduce ICE friction, a clean air filter to reduce pumping losses, a swap out of the transmission fluid to the Prius-II’s WS-ATF to reduce gear mesh losses and an EBH (Electric Block Heater) to help bring up coolant temp quickly so as to help improve upon the warm-up hit will all help improve upon her capabilities tremendously. I did not swap out the tranny fluid or install an EBH for the week and a half I had with her but everything else was good to go.
Prius-I’s warm-up fuel economy hit
. From the time you turn the key and shift into Drive, the Prius’-I’s ICE is only spinning to warm-up the coolant and CAT and/or force charge the pack while under a low load acceleration from dead cold. Load as displayed by the ScanGauge-II was down in the high 20 to high 30% range while forced charging occurred and I do not believe this range to be an efficient one with the ICE spinning at 1,250 - 1,350 RPM going nowhere. When first driving her off normally for a commute or segment from dead cold, it was not uncommon to see that segments mpg down in the high 30’s/low 40’s after any 2-mile distance from an initial starting point. This kind of Fuel economy from a compact automobile during warm-up was unacceptable. What was found to work reasonably well during the warm-up phase was to propel her to a speed between 20 and 30 mph via the pack while the ICE is performing its pre-programmed warm-up routine and FAS which entailed a shift to N, key her off and back on again to reboot and achieve a powerless glide all the way down to 0 mph. You must have an absolutely un-impeded path in front and from behind in which to glide back down to 0 mph because there is no way for you to start her back up and continue driving until you have come to a complete stop, placed her in Park, shut down and rebooted. On the second or third pulse, the ICE would begin propelling the Prius-I like normal as well as force charging the pack during the acceleration which is exactly what was needed at that point in time. This warm-up technique yielded upwards of 80 mpg, a SoC recovering from an initial half to full over a 2 - 3 mile distance and a coolant temperature at a minimum of 155 degrees F. This is the minimum temperature found for the Prius-I’s hybrid functions to operate seamlessly. I did not find a better way other then to install an EBH (Engine Block Heater). Again, the caveats to this warm-up FAS method are extreme so use it only in a subdivision or parking lot where you can actually come to a complete stop at a stop sign or other traffic impediment right after bringing her up to speed from dead cold. If propulsion power was needed for any reason, you are dead in the water with no place to go but off the road to a complete stop.
Pulse and Glide
. There are a few rules that should be considered whenever and wherever possible. Once the Prius-I is completely warmed up with coolant temps above a minimum 155 degrees F, she can transition from a pulse to a glide and back again relatively easily. The issues I experienced are trying to hold a pure glide (no arrows) from a top speed to a lower speed target, entering into an ICE-Off Glide before reaching 35 mph, finding a relatively efficient pulse rate and finally the poor resolution of the SoC mimic not allowing you to know where the actual SoC may lye. Now would be a good time to review the P&G plus Warp Stealth in the Prius II for maximum FE
article. The Prius-I can be manipulated into the exact same modes using similar techniques for excellent FE but not with quite the same ease or high end results.
Gliding. Because a Glide is the key to optimizing FE in all vehicles, it is very important that a successful no-arrow glide be initiated and held until the lower speed target is reached in the Prius-I. Holding a no-arrow glide is not quite as easy as can be achieved in the Prius-II but with a quick transition to a no arrow glide per the mimic and a shift of the gear lever from D to N once you have reached 31 mph and heading down from the higher speed target, she will drop into a powerless Glide efficiently and with ease.
ICE-Off glide. This was a bit more frustrating. With a SoC showing either full or half and coolant temps well into the 180’s, sometimes her ICE would simply not shut down when entering into a glide. You could achieve a no-arrow glide but the ICE would continue to idle away consuming precious fuel for some unknown reason? In order to guarantee an ICE-Off glide each and every time, a minimum of 35 mph from the previous pulse or steady state operation must be reached. Once 35 was breached, an ICE-Off Glide was never an issue.
Pulse rates (Accelerations). In the Prius-II, some use the ScanGauge II’s tach or load while others use the OEM iFCD to gauge a particular Pulse rate. In the Prius-I, her ICE is power constrained on the top end by MG2 assisting at lower RPM’s and higher loads. Whenever I saw or felt this action help accelerate the Prius-I, her iFCD would drop into the high teens from 20 - 30 mph. The following mimic shows a pulse rate I would not
suggest using under any acceleration scenario other then an emergency whether that be to reach a steady state cruise or during a P&G scenario.
- Sub 20 mpg Pulse w/ little additional acceleration: Power from ICE and MGSets to both the wheels and the pack.
By easing back on the accelerator pedal just a touch once MG2 began to assist per the mimic above, you should achieve near the same acceleration rate (seat of the pants measurement) but with a 20 + mpg result vs. Sub-20’s like above thus leading to the success I feel many Prius-I owners can achieve for themselves. The standard Pulse (ICE to the wheels and through MG1 to the Pack) as seen below appeared to yield the best results in my week and half behind the wheel?
- 20 + mpg pulse w/ a Full SoC: Power from ICE to Wheels and ICE to MG1 to the pack.
Poor resolution of the Prius-I SoC. As depicted in the pics below, the Prius-I displays the SoC as either Full or Half. We know the pack has a SoC range of almost 40% but with the simplistic Full/Half mimic provided, you do not have any idea as to what the actual SoC is and thus had to use EV very conservatively.
SoC Full --------------
With the above, the following technique whenever a slower speed range P&G scenario can be achieved should be considered. Starting from a Full SoC, accelerate to 20 mph under EV and ignite the ICE with a quick jab and return of the accelerator pedal. Use the proper pulse energy mimic as shown above to achieve a higher speed target of at least 35 mph. Let off and once Regen is seen, place her gear selector into N as your speed drops to 31 mph or below as the ICE is already shut down. Arrow free Glide down to 15 mph. Place the gear selector back into D, EV back up to 20 mph, re-engage the ICE and again pulse back up to at least 35 mph. Repeat the sequence except only glide down to 20 mph and immediately accelerate back up to 35 mph plus with no use of EV. Continue to use the 20 - 35 mph or higher Pulse and Glide range without any EV on the bottom end as long as possible. If you see the SoC mimic drop to ½, you may need to run the next two pulses up to maybe 37 to 40 mph to bring the SoC back to full and allow a more efficient pulse range afterwards. With the SoC at half, MG1 is drawing hard off the ICE during a Pulse thus preventing a 20 + mpg acceleration rate. If you see the half SoC mimic appear, it is best to Pulse to higher speeds at an even lower pulse rate so as to allow more time for MG1 to fill the pack back up as soon as possible. If you have a downhill section, you can use Regen to help bring the SoC back to full. Either way, you should attempt to bring her SoC back to full within 2 P&G cycles or your maximum FE success rate has been diminished severely
Lower speed highway
. There was an interesting phenomenon that appeared between 48 - 52 mph after a long stretch of P&G that had me somewhat confused. Even today I am not sure the solution is completely sound? While traveling at speeds between 47 and 52 mph, I would sometimes see long bouts of 52 - 54 mpg as if running in a forced charge mode. A minute or two later, I would see the iFCD running at 110 - 112 mpg and the Energy mimic was showing full Assist when none was called for. This cycle would continue for quite some time after reaching the Interstate. If I sped up, the issue went away and so did the great 48 - 52 mph, 75 mpg highway fuel economy
I tried to DWL and drop load off almost completely during what appeared to be a force charge to no avail. Nothing I did with the accelerator pedal to counteract the Forced Charge/Full Assist effects seemed to stop this cycle other then speeding up and loading the ICE up a lot harder then what I deemed appropriate and sacrificing FE in the process. After 10 - 20 miles, this cycle would usually disappear but either way, while it was happening; it was tough to maintain 75 + mpg no matter her speed. During a night shift drive, I noticed this issue subsided soon after I turned on the headlights. Again, I do not have a reason as to the why this should happen but it was rearing up with little input on my part. On the second to last day heading into work, I was running into this low load highway speed cycle yet again and decided to try using CC (Cruise Control). CC has never worked for maximizing FE in any other automobile I have ever been behind the wheel of but this full assist to forced charge cycle stopped almost immediately afterwards? I was able to maintain the iFCD in the 75 mpg range on the flats as well as see a number of 5-minute bars at 75 + mpg without any effort other then holding a very slow and low load speed while RR under CC. Whenever I would run a hill, I would dis-engage CC and speed up a touch coming into the trough, DWL up, Warp stealth down and re-engage CC as soon as my previous speed target was reached. I do not know why it worked but it did and that is all I cared about
I have no idea as to the inner workings of the SoC algorithm but CC at 48 mph settled the cycle down and yielded darn good FE while traversing the flatter sections. Saying the Prius-I exceeded my expectations would be an understatement.
Heavy stop and crawl highway traffic conditions
. This is where P&G’ing and/or EV’ing while DWB comes to play. With every slow down to 0 mph, a little regen from some distance away would bring her speed down gently all the while increasing the SoC (the mimic was usually full given the higher speed highway run into the traffic jam). When stopped and movement begins, a gentle acceleration under EV until a either a gap appeared to open up for a 35 mph + Pulse with a Glide back down, slow speed EV to the top of the next hill/overpass, whatever and glide back down in N, or simply re-ignite the ICE, accelerate back up to whatever traffic would allow and hopefully glide back down ICE-Off even if 35 mph was not reached. Achieving ICE-Off was successful when pulsing up to < 35 mph maybe 75% of the time but when the ICE did not shut down, you paid dearly for the glide back down to 0 mph and waiting for the ICE to stop while parked with everybody else. Running her up to higher speeds as traffic allowed when it did open up allowed for a nice charge on the pack so as to cover overhead and allow a few blocks of EV which is exactly what makes the Prius-I so darn effective in this type of traffic scenario. In one 10 mile stop and crawl on Interstate I-294 just south of O’Hare airport in Chicago, I saw 4 of the 6, 5-minute bars pegged in fact. Fuel economy over any given period while stuck in a traffic jam allows her to achieve the mid 80’s to low 90’s without so much as a few accelerator pedal manipulations if you are willing to take her to those levels.
Higher speed highways
. This is an area where all vehicles drop off quickly but the Prius-I appeared to drop off faster then just about anything I have driven other then an HCH-I or Insight dropping out of lean-burn as speed increased. For every mph above 50, I was losing ~ 1 - 1.5 mpg which appears harsh at first but even at 60, she would hold onto 60 mpg once setup. The good thing is whenever an opportunity presents itself to slow to a stop, to a lower speed or you have a long downhill ahead, warp stealth can and should be taken advantage of at every opportunity. By placing her into Warp stealth, you are minimizing energy conversion back to the pack under regen, you are in fuel cut for the time she is in this mode and you are not losing much in the way of speed depending on how steep the downhill section is. You are however dragging the packs SoC down some while MG1 draws current in order to spin the motor over. Because the energy mimic was so course, I did what I could to maintain the ICE spinning between 1,000 and 1,200 RPM via MG1 (somewhat speed dependant for some reason?) and attempt to hold a no arrow warp stealth. That last part takes a delicate pedal balance and as your SoC or speed droops, you will be making fine adjustments to the accelerator pedal so as to try and maintain this no-arrow warp-stealth condition at highway speeds. Without a Can-View or Graham scanner, I am not sure what the current magnitudes or directions were or even if this no-arrow mode even exits under the hood? Given the Energy mimic shows current flow back and forth between regen and standard warp stealth, I used this no-arrow warp-stealth mode as yet another fuel conserving technique and used it anytime I was slowing from 60 + down though 41 before entering into a pure Glide. I wish there was better news with regard to her higher speed highway fuel economy but given she was pushed for what she was worth (not for what she was not
), that leaves me flying a little blind on the top end.
I want to add that what many believe to be a very fuel efficient RPM range in the Prius II’s 1.5 (1,700 - 2,300 RPM) was not where I found the highest FE from in the Prius-I. With the energy mimic pointing to a 1250 - 1400 RPM range during the pulse so as to keep MG2 from assisting, I found a similar RPM range to work extremely well even at highways speeds. While climbing any lengthy steeper segment, I would run her up inside a 1,700 - 2,100 RPM range as that was sometimes needed but loafing along down the highway at the same 1,250 to 1,450 range appeared to maximize her somewhat steady state fuel economy tremendously. There was not much power available down that low but her FE figures told me this is where she wanted to be. I hope you find the same.
. All tanks below were consumed using an initial tank top off to final fill tank top off.
Short ScanGauge Calibration Tank
Temps from 63 - 76 degrees F and 20% rain. MFD = 78.6 with the std. setup but non calibrated SG-II = 73.5 after 191.0 miles.
I allowed my wife drive almost 20 miles and I drove the rest back to a local gas station for the short calibration tank. 234.0 miles on 3.306 gallons = 70.78 mpg
. Calibration commute(s) yielded a + 1% speed/distance offset and a + 3.3% Gallons consumed offset over this short calibration tank.
Full Review Tank
Temps from 63 – 81 degrees F. MFD = 79.3 with the SG-II = 74.5 after 189.3 miles.
Temps from 64 – 84 degrees F. MFD = 78.7 with the SG-II = 74.0 after 381.2 miles.
Temps from 68 – 86 degrees F. MFD = 78.9 with the SG-II = 74.3 after 575.6 miles.
Temps from 72 – 84 degrees F. MFD = 78.8 with the SG-II = 74.1 after 769.6 miles.
Temps from 75 – 82 degrees F. MFD = 79.3 with the SG-II = 74.5 after 947.3 miles. 2.000 gallon fillup from gas can.
Temps from 81 – 82 degrees F. MFD = 79.3 with the SG-II = 74.5 after 963.8 miles.
Fuel Starve occurred at 947.3 miles out. Top off fill calibration dropped fuel consumption offset to + 2.3% with mph/distance at 0% offset. 963.8 miles on 12.821 gallons (10.821 gallons + 2.000 gallon from can) = 75.17 mpg
Final Short Tank before she went back to her owner.
Temps from 72 – 83 degrees F. MFD = 82.3 mpg with the SG-II = 78.4 after 198.0 miles.
Temps from 75 – 88 degrees F. MFD = 83.4 mpg with the SG-II = 79.1 after 392.5 miles.
ScanGauge-II for final commute home and tank: 83.6 mpg and 79.1 mpg.
Top off to Top off for final fill Fuel Economy. 392.5 miles on 4.96 gallons = 79.13 mpg
Top off to Top off from initial fill to final fill, observed Fuel Economy: 1590.3 miles on 21.087 gallons = 75.416 mpg
. With a little help from you, the Prius-I can reach an area few may have thought possible in the past. I would highly recommend that you place some of these techniques into practice at your earliest convenience but not without first practicing them on an empty and desolate country road so they become second nature and only under the safest conditions. The Energy and Consumption screens as well as a Scangauge can overwhelm you at first and it is best to train yourself gradually rather then “I can do all of this tomorrow” and getting someone injured as well as achieving somewhat poor results in the short term. Once you have the tools in your toolbox, it should not be out of your realm to achieve the mid 60’s to low 70’s while driving a lower speed highway commute, 70’s and 80’s over very short trips around town in the summer, and mid 80’s to mid-90’s when you can let it all go on the back desolate roads you may available to you. It was not uncommon to take her from dead cold in 70 degree temps to the low to mid 90’s within 15 miles of her starting point using every tool in the arsenal. Of course traffic and roadway conditions may dictate a far less fuel efficient segment but even so, use you head with the tools provided and she will reward you many times over.
If you have the type of commute allowing you to be untouched by other drivers in a lower speed suburban type environment, 1,000 miles to a tank would not be a problem. As speeds climb, that possibility diminishes quickly although excellent FE is still available with the right application of the proper tool at the appropriate time no matter when and where you drive.
I would like to thank both Wayne Mitchell and Doug Schaeffer for their technical expertise and especially Cheryl Appel of the Madison Hybrid Group for the use of her Prius-I for a week + so as to not only gain experience with this fine piece of automotive history but better yet, find out what it was capable of in the process.
Cheryl and her 2002 Prius-I.
Thank you Cheryl!