Got a prius, should be interesting to mess with....

[ps2fixer]

That's why I wanted a fairly long road to do the testing on. I couldn't check SOC exactly, but the indicator was 2 bars from full, so 6/8 the whole time. I'm sure the testing is far from perfect, but the results I got matched my theory. My main focus was the different take off styles, pretty much keeping the engine a little off idle to around 2000 rpm seems to give similar performance.

Tires are currently at 50psi, max sidewall is 44psi.

I'm not entirely sure what's causing my car's mpg to seem to be lower than what other people seem to get. Hopefully I can figure it out. Main 4 items (or combo of them all) would be high miles on engine/battery, bad wheel bearing (and likely alignment), and the front end damage. Pretty easy to fix everything besides the engine/battery if that's the root cause. I was thinking how I take off and brake was a large factor, but it seems like that's not it.

[mpg_numbers_guy]

If your battery is staying at 6/8 bars most of the time then you probably have a healthy battery....a telltale sign of a battery that is about to fail is one that goes from full to empty repeatedly and rapidly in just normal driving (not counting long descents and regen situations, or prolonged use of EV mode). Dr. Prius gives more info with a diagnostic test that lets you test the individual resistances of each cell in the battery, bad cells typically have resistances that are significantly different from the rest of the pack.

[Blacktree]

The brand / model of the tires can make a big difference, as well. For example, some of the 1st gen Insight owners report a loss of 8-10 mpg when switching to a different tire (from stock).

I don't know offhand what tires the Prius 2 came with from the factory. But my car has the Firestone Fuel Fighter tires, which have a reputation for good fuel economy. They're also kinda pricey. So I'm glad the previous owner bought them.

Also, I'm using a pretty mild tire pressure increase. Stock tire pressures are 35 psi front / 32 psi rear. I increased it by 3. So now it's 38 psi front / 35 psi rear. I didn't want to use really high tire pressures and prematurely wear my not-so-cheap tires.

[ps2fixer]

I'll have to check the hybrid battery health once I find my scangauge or buy a 2nd one. I'm guessing the battery is doing alright, I'm pretty sure it's not about to fail since the bar graph indicator rarely moves.

@Blacktree

I've been running max side wall pressure on tires for at least 170k miles on different vehicles, cars, trucks, etc. My dad's a mechanic, he ALWAYS uses max sidewall pressure for his vehicles as well. We both have never had bad tread wear unless the vehicle's alignment was bad. The low end cheap tires I've had busted belts on a couple of times, but never had a problem with a quality brand name tire. If it say's made in China, it might be a "China bomb" tire so lower pressure might be best for those.

If you recall the firestone recall back in the 90's, the issue was partially caused from under inflated tires by Ford, I wish there was a study done with running the tires at higher pressure, max side wall, etc to see if it effected failure rate since the tires did have a manufacturing issue as well. My dad said one of the training sessions he went to had a rep from one of the tire manufactures, I can't remember the exact figure, but something like 10% under max side wall pressure the tire manufacturer counts as under inflated.

Publicly, Firestone argued that Ford's recommended 26 psi inflation pressure was too low and should have been 30 psi. In addition Firestone argued that the Explorer was abnormally dangerous and prone to rollovers in the event of a tire failure, leading to more injuries and fatalities.

Ford argued that the Explorer was no more dangerous than any other SUV and that the accident rate for Explorers with Goodyear tires was far lower than for Explorers with Firestone tires. Ford also argued that there was something wrong with the design of Firestone tires and with the manufacturing of those tires with Benzene.

https://www.townfairtire.com/blog/wh...ntroversy.html

At the few different places dad worked, most of the auto shops like to inflate the tires to 35-40psi at least in our area even if the car suggests 26psi.

Anyway, I'm not trying to twist your arm to running higher pressure, just putting out what I know/understand on tires. If I was in your situation, I'd just run 40psi front and rear. It's within the 10% max side wall range, but isn't super high to cause tire failure. The tires are rated with a max sidewall pressure, and there's a built in safety margin. Most likely the tires can handle twice the sidewall pressure or more before they blow up.

Just like the firefighter air tanks, the ones I use are rated at 4500psi, hydro testing is done at around 10k psi, and at the factory they are tested to failure which I think was 15k psi. The fire fighter tank we use for PCP air rifles, and my dad found that there's an adapter to adapt the tank to air up car tires. We used it once and was able to fill up all 4 tires on a car off it that had 3 flat tires and one low. We still had some pressure left (2200psi if I remember right). Very handy for the kind of stuff we do. A normal air tank at 100psi can do about 1 to 1.5 tires when completely flat.



I've always went for somewhat cheap but name brand tires. My corolla's tires were nothing special, rated for 50k miles, 44psi max sidewall, and they were budget tires, not LLR tires. I put about 80k miles on them and the tire wasn't to the wear bars yet. I did drive on winter tires during winter for a year or two so I'm not sure how many miles the tires really have but should be over the 50k rating. If I remember right they were like $55 per tire back around 2013. I haven't dove the car quite a while, the metal that the gas tank straps bolt to rusted out. I basically did no maintenance on the car, it's truly a beater before I even got it. Front end has been clunking and making noise since I've owned it, hasn't changed at all in the 80k miles I drove it lol. I think it had a tie rod a little sloppy on the driver's side and the strut mount was the main source of all the noise.

I kind of wish I could run across a prius that's super cheap with a bad engine/trans, I think it would be interesting to swap in a 7a-fe corolla engine and trans and work out the CV axles to fit the prius. I know that engine does real good for mpg would be interesting to see how it does with a car that's more areo but heavier. At the same time, it would be interesting to transplant the prius system into a 93-97 corolla and see what kind of mpg it gets. I guess just looking at a 2007 Camry's mpg should be an alright reference for hybrid vs non-hybrid for the same car. Hybrid mpg is 34mpg, non-hybrid (same engine but "normal" built) 31mpg for highway. Looks like around 10% difference. My corolla got 38-44mpg, so with the prius setup in it, I'd guess it would get around 45-50mpg, pretty much the same as in a prius, at least for the one I have. I guess that suggests the overall areo drag should be similar for the smaller corolla (with my minor mods) vs the larger prius.

I'll have to brainstorm some ideas for the Prius. I think the style of testing I was doing is good enough to get an idea of mpg with out needing to go 100's of miles, I'm sure it's far from perfect though.

[hayden55]

Yup gen 3 targets 60 +/- 2% SOC as a midpoint. It will charge up below and burn it off above. If you get a scan gauge you should be able to see where load peaks and that will be around your peak BSFC I assume similar to the graph posted before. My gen 3 is running a non-EGR map and peak load used to be something like 92% the entire time it never moved, but now it's 60-75-85-90 depending on rpm, and peak is achieved around 2050 rpm.
I pulse and glide my gen 3 prius with the SOC gauge and RPM gauge and Fwt gauge on my scan gauge with decent success even with my EGR delete and 205/70/15 tires (90 day mpg is about 52mpg still). Gen 3 will let you shut the engine off at 45mph and below and with my tires I can do engine off up to 46. If it makes you feel better i only get like 42mpg on the interstate going 70mph.

Pretty much my main goal when driving is to stay between the midpoint plus and minus for best mpg so I use pulse and glide to get the most out of the extra energy. Going above is okay not a big deal but going below really kills the mpg. Basically just a stop start system for me to get pretty good gas mileage. On your battery I wouldn't worry about it being bad as you really don't need to rely on it a ton besides using it for stop and start. Driving in EV mode is mostly a detriment to my mpg unless i just need to inch forward 50 feet to a stop sign. Each stop start registers on my 2010 gen 3 as 0.4% SOC.

[ps2fixer]

Interesting numbers. only 42mpg at 70mph seems low. Mine was hanging around 45mpg, but that was just eye balling it, I didn't average it out on a trip or anything and that didn't account for take off and slow down, so 42 sounds similar to mine.

I really need to find or buy another scan gauge, since there's no real gauges on this car, I can't even check if the coolant temp is normal or not. I kind of hate newer cars, such a lack of info lol. I'm wondering if maybe the thermostat is sticking open. I drove to the post office 55mph, and on the way back I drove 45mph. I was only seeing around 50-53mpg for the instant read out. Post office is 5 miles away, 10 miles round trip. Seems like just a slightly cooler day and the mpg drops super hard on this car. I'd dare to say if I drove my corolla similarly I'd get similar mpg for the short trips. I didn't think that car was anything special for mpg. I have an echo that I just fixed up, but I'd rather have a hatch back.

I've only been using the in car readout, so I know it's not the most amazing for knowing the mileage, once I hit closer to 400-500 miles on the tank I'll have a better idea of what the true mileage is.

[ps2fixer]

I did a temp lower grill block, fancy packaging tape. I did the same on my corolla to test the effect lol. Anyway, temps are much colder today than the last trip to the post office, drove the same speeds though, 55 to, 45 back. Indication said 48mpg. Car seems to coast farther now.

Check engine light came back on, I suspect it's P0420 returning, so the cats are bad, or the secondary o2 sensor is junk. Kind of funny I paid extra for the car to have the cat left on it. I wonder if it's plugging up and effecting how the engine runs.

I figured I'd do a seafoam treatment, 1 can down the intake, soak, and run hard for a trip. I ended up taking it out on the express way for 25 miles or so. I'm not sure if that can help clean the cat or not, I'll probably need to try to get one of the cat clearer products and see if that helps much. I suspect the engine consumes oil, and the cat might be coated in some oil preventing it from lighting off. Hoping that the mechanic in a can can get it to fire off and burn the junk out. Will see how that does next time I go up town and grab the can of the stuff, worth a shot at least. I threw 1/2 can in the gas tank, theory is it helps clean the injectors too.

Clearly the trip out wasn't easy on the gas, traveling 60mph was around 40-42mpg if I remember right on the dash. Reset it once I got on the highway at 80mph and it was reading around 32mpg, I swear my corolla did better at that speed lol (I rarely go that fast). On the way back, I set it back down to 60mph and averaged 49mpg from entrance ramp to stopped at the exit ramp which seems slightly better than before but not enough data to really mean much. On the way back I planned to go 55mph, but had a guy try to hit me at the round about, so figured I'd just go 45mph since I didn't care about their feelings much. I averaged from the highway to my house 57.5mpg. That's not half bad, that's about 10 miles. Clearly that's with an already warmed up car, air temp was around 40F starting, 37F when I finished.

[ps2fixer]

Oh, I also have had some ideas for possible mods, but not sure if they would give a net benefit.

First up is the transmission, is there much of an effect for cold vs warm trans on mpg for the CVT design? A normal transmission has the oil pump and such and it has to apply pressure to clutches and all of that to function, so the cold fluid effects things quite a bit. I'm guessing on the CVT there's not much to gain and the heat from the electric motors probably heats it up pretty fast on it's own.

Next thing is a simple idea, but not sure if it would be a net gain or not. Basic idea is a block heater, but it's powered off the 12v system, so ultimately the power comes from the engine. Gain in theory would be to warm the oil up to operating temps faster, of course the negative is higher load while the engine is cold. Clearly plugging in a block heater would be more effective, but I'm not looking to plug in the car all the time, my property isn't setup with an easy access outside outlet anyway (my diesel gets to do cold starts in the winter purely off the glow plugs).

I also found a thread of someone testing the front belly pan installed vs removed for the mpg effect at 70mph if I remember right, and over a back and forth trip of 32 miles, they saw 1mpg difference (without was 1mpg less). Currently my car basically has 1/2 a belly pan, while changing the oil, the oil filter wasn't easy to get to, so needed the extra room. The same side is where the damage is at, and all of the bolts are rusted up enough to just snap off so not exactly easy to just reattach as it was intended anyway. I'm wondering if anyone has looked into making a more full belly pan, and if it effects mpg much on these cars. Another similar idea I had was adding an air dam up front to push more air around the car instead of under it. Clearly it would need to be something flexible so it can go up drives and such and not just break off.

I noticed the rear bumper can catch a bit of air too, seems like there's no cover back there or it's missing, probably small gains if anything.

There doesn't seem to be a whole lot that can be done with this car, all the simple stuff is already done factory =). I guess the next thing would be to extend the roof line to make it more into a boat tail. I'm not a huge fan of the look, but might be something I'd play around with if there's enough gains to justify it.

I've been thinking mainly about quicker engine warm up times, and areo mainly. I need to move the "cold" air intake over so it's more of a warm air intake, or just remove the section of tubing so it's sucking from under the hood, probably not much of an effect I'd guess, but maybe it will make it more efficient at lower loads. I suspect another target would be to seal up the hood better to help hold the heat in the engine bay. I did that on my corolla and with out the hood insulation, it still held heat for a long time. My power stroke diesel really needs that mod, even though the big chunk of cast iron does a pretty good job staying warm for quite a while lol.

Am I missing any other low hanging fruit? Once the wheel bearing is fixed, I'll have to measure up the front tires to see if the alignment is good, tire wear indicates the alignment is good.

[Blacktree]

For faster engine warmup, you'll want to block the upper grille. The upper grille provides airflow for engine cooling. The lower grille helps cool the inverter, and also some engine cooling. Running the inverter hotter (i.e. with a lower grille block) will probably reduce its efficiency.

I think there are some aero gains to be made on the underside. The car comes with some underside panels, but they're far from perfect. For example, the entire passenger side, behind the rear wheels, is left open. I'm guessing they didn't want any plastic panels anywhere near the exhaust. But some heat shielding should help with that.

[ps2fixer]

Looks like the radiator is assembled all together, so the engine coolant would heat/cool the inverter coolant to an extent on it's own. After I did that 80mph test I pulled over and checked the inverter temp. It was warm not hot, maybe like 100F, this was down lower on the inverter, clearly not the cover. I'll have to keep an eye on it, but I suspect the cooling for it is way over kill. Looks like there's no xgauge for the scan gauge for inverter temp, 3rd gen has a bunch of temps and such.




Anyway, over 250 miles on this tank so far, got 3 bars left on the gas gauge, getting close to 1/4 tank. I suspect there's some sort of reserve too. The going 80mph really sucked the gas down fast.

Small update on things, I drove the car to a farther away post office (closes later) so figured it would give a nice trip to check mpg on. Started out 45mph with the cold engine since it seems to effect the mpg a ton at first at least. Once I got to the main road where there's a ton of traffic, I just went 55mph (basically everyone goes 60-65, some 70). On the way back I stopped at my dad's place for a bit and the engine cooled off enough to start up before power was needed (no hvac) but round trip driving mostly normal besides the 45mph area I hit over 50mpg, I think the trip computer said 51.2mpg. Not bad for the longer trips. I have a feeling getting 50mpg+ going to the close post office might be a lofty goal at 55mph, but at 45mph I think it can be done pretty easily.

I ended up buying a scan gauge, brand new on ebay for $140. The used ones are too close to new price, there's no real benefit buying used at those prices. I'm blown away the ultra gauges are so expensive now, they used to be like $50-55ish. I could really they they were cheaper built, the switches aren't great, and they aren't the most amazing at turning off, have had it kill the battery in my corolla a few times if it sat long enough, might be a side effect of cold weather in the winter too. I had zero problems with the scanguage.

Anyway, upper grill block I'll probably do, just the lower one was so much easier to do. Been pretty busy with my business, so haven't had a whole lot of time to mess with the car. Little things here and there. Need to assemble the back of the car together from doing the struts yet lol.

I wonder what the best way to stress test the inverter, and is there any known limits for temps? Generally speaking from the computer side of things, most devices are designed for 100C max, some lower temp stuff is 80C, but for inside power supplies and such 125C isn't uncommon. Clearly the coolant is going to the parts generating the most heat, likely not the capacitors. I'd guess their max voltage would be at least 80C (176F).

It shouldn't be too hard to run a temp probe and a cheap digital temp gauge somewhere to monitor the temps. Get a reading with block on at some consistent way of testing it, maybe do the 80mph thing again but at say 60mph and monitor average temp, then repeat with the grill block off. It's just packaging tape, so not like it's expensive to reapply.

I wonder if smooth hub caps would give much of an effect on the prius. I think I had a slight gain on my corolla. I just used simple coroplast zip tied to the rims and spray bombed to somewhat match the body color.

It's been a long time since I read about air dams and such, if I remember right, the concept was if the areo under the vehicle wasn't very good, the air dam was the simplest solution. With an air dam, I don't think there's much benefit from the under body panels since so much less air gets pushed under the car. I suspect a full underbelly pan would give some gains, clearly have to be careful about the exhaust, and the engine bay needs enough of a gap for the air going through the radiator to flow out of. Seems like the ideal setup would be to vent to the side of the vehicle where there would be a slight vacuum over some little vents. I suspect even better would be to use the vacuum at the rear of the car, but that's a long run.

I read on some prius models, the engine coolant went to the first cat to help with quicker warm ups. I'm guessing that's a 3rd gen thing, I don't recall seeing anything like that for 2nd gen. It would be neat to use the exhaust heat to help warm up the engine faster, say a heat exchanger to the engine oil pan and some sort of coolant heat exchanger. Clearly the issue is working with something that can handle both temp extremes (-10F or so to the max temp of the exhaust system). It would be nice to be able to disable the system once the engine is wamed up, since don't want to add more cooling demands. Also not sure what the effect is on cooling the exhaust gases, I suspect it shouldn't have much effect on how the engine runs since it should be a gradual thing.

Just for giggles, has anyone ran a boat tail on a prius? I've seen some pics online, but I don't see any mpg claims. Best I've seen was a box behind a prius and their mpg was like 51 average, the fuel log showed peaks of around 65 mph. No details on the trips though, like city driving, pulse and glide, higherway/express way driving, etc. The areocivic does amazing on mpg, I suspect a prius modified in a similar manner should give similar or better results even though it's a bigger/heavier car.