MPG 2008 Prius=28mpg Winter; 35 Summer

If I had purchased a Prius and only made short trips, I would be disappointed too. I had no idea the first 5-10 mins were the worse until after I had the car and also read about it on PriusChat. I know -- bad research on my part. But be that as it may, I would probably have wrongly assumed it would do as well on short trips and been upset about it. True, it still beats out many other cars -- but I bought the Prius to see the golden 50 at least. Fortunately, I drive highway so that's what I am seeing.

 

Wow, if I got low 40's or into the 30's mpg average, I'd be seriously pissed given the cost of this car. Saving all gas receipts and snapping photos of the MFD averages would be part of evidence collecting.

I luckily got a very good unit. It snapped right into ~ 52 ish mpg when new (13 miles total) and has hovered around 55 mpg average on the MFD. Sometimes I do 2 mile trips or like today, 10 minute trips, twice.

My gas receipts back it up with over 54 mpg over 3 tankfuls average. I check tires often to be at 38/36 fr/rear. I don't do anything special, but I tend to drive around posted speed limits and I try to brake gently to slow or stop. Toyota said to go gently on new brakes, so that habit has stuck. I want the car to last a looong time, it is expensive.

anyrate, I hope you can get to the bottom of things.

 

Mark,

It isn't clear to me why your mileage is so low. (Ignore some of the ill considered personal criticisms/comments about your driving.) With similar temps to what you quoted we are still getting in the mid 40's with the upper grill blocked (dropped to around 40 when the original insulation blew out--use plastic cable ties, don't rely on "compression fit.") The car gets mostly short commutes of about 3 to 6 miles with many hills and stops. (Local gas has 10% ethanol as well.) The trips take about 10-15 mins typically.

Yes, the warm up cycle hurts mileage but there is some room to manage it. Since most of the short runs are mostly at low speeds there is some compensation. One of my shortest regular round trips still gets over 50 mpg on average, and mid/upper 50's in warmer weather.

Did you have alignment checked? This should have been free, but not if you wait too long. <nudge, nudge> It's typically something like 1 year/12,000 miles IIRC--at 13,000 I would expect the dealer to still cover it under the new vehicle warranty (but who knows what any dealer will or won't do?) Since you seem to have some sort of record of questioning the low mpg with the dealer/Toyota, you have documentation for covering the alignment under the original warranty. If your alignment is out you are likely to have greater rolling resistance, tire wear, perhaps a bit of pull that requires steering input, and (if the thrust angle is a bit askew as a result) you will have less clean aerodynamics and therefore more drag.

The question I still haven't seen answered is whether the ICE is off frequently or if it is running most of the time, particularly when idling at lights, but also on low speed in town driving where the car should be able to glide long distances. If it is running most of the time even when warmed up at low speed, then it is going to really impact mileage, and in such a case interstate highway mileage will look good by comparison.

Did you ever check the oil level? Overfilling is chronic with the Prius thanks to Toyota's inaccurate documentation on the subject--a slightly incorrect fill quantity. It can sometimes reduce mileage incrementally, or cause other more serious issues if it is greatly overfilled.

The rule of thumb for acceleration is to hold the indicated MPG at about 1/2 of the indicated MPH up until 35 mph or so (check around, there have been some recent posts on this by gurus.) Going much over this will hurt gas mileage, but driving too daintily on acceleration can be counterproductive from what I've seen. This is especially true with hills and such.

As for your questions about grill blocking, that is well covered in other recent threads. The mechanic does not understand how the Prius operates and how important having the engine off (by conserving engine heat) is to the mileage (and comfort of the driver to some degree--pun intended.)

Ditto for EBH, it is covered in other threads and you should study those for answers. I don't have one. It's going to have some of the same impact as a garage (and the same limitation of only being useful for trips starting from the house. I can tell that the garage makes a difference. When I park in a lot and come back to the car after it has been sitting for several hours at ~30 F the ICE works stubbornly to warm up the car even if I'm not running the heat. I don't like the way the car manages the heat/AC in the first few minutes of driving if left to its own devices.

 

Shawn,

You stated that you drive 10-15 min trips, but Mark is driving 5-10 minute hops ... and I really think that's the big issue in this case. I know with my Prius -- it's garage kept (no EBH), and on those warmer days where the ICE doesn't require as much time to warm up I still get lousy FE during the first 5-minute segment. Occasionally it's over 25, but typically it's right on that 25 mpg line. And I average 52-55 mpg per tankful.

Mark, your mechanic is correct that the EBH will only help you on the first use of your Prius from home if you are unable to plug it in while you're out and about, and if you're making a lot of short hops in cold weather. But the EBH and blocking together may help a little. Of course, remove the block in warmer weather. But I do think the short/frequent 5-10 minute jaunts (where you are stopping the car, leaving it awhile, restarting it again to go another 5-10 mins) will reduce the mpg noticeably.

Maybe someone can correct me if I'm wrong about this.

 

For some reason it has not been mentioned until the very last few posts. BLOCK YOUR GRILL! At 45F the engine will NEVER get to operating temperature if you are running any heat or defrost. Add in short trips and you'll only add to the problem! We drive 15 miles to town, with our grill blocked completely except for 1/2 of the top slat. Even at that, at 45f it takes the entire 15 miles for the temp gauge to get to 185f. That is with all the heat OFF!

185f is where the thermostat BEGINS to open, it is fully open at ~205f. Running an engine too cool makes it run very inefficiently. Even without a scan gauge you can run with the grill blocked all the time if temps are below ~70f. We have driven cross country 3 times, once in the summer, with the grill 75% blocked and never saw a engine temp over 205f, even with the AC going. We get ~52-54mpg routinely. We've only had one tank under 50 mpg.

If you mileage is as bad as you say, inflate your tires, block your grill, and learn how to drive using the mfd.

Icarus

 

I have to disagree. The 5-10 minute jaunts with long gaps will kill the mileage. Cold starts are the worst for mileage. EBH will help a bit, but grill blocking will work wonders.

I also contend that you can leave the blocking in as long as the temp is below ~70f, but do your own research, and buy a scan gauge. Cheap given what it will tell you,

Icarus

 

I keep hearing that, but I've never seen it. I have had it dip pretty low (for me) during cold weather at night when a wreck had traffic at a near standstill. If the engine is cold and I have to do stop and go then accelerate to interstate speeds I see low 30's for the first five. My tanks average 47-50 mpg so I don't think there is anything special about the car or driver in my case.

For instance: I did three short hops today, 9 miles total, 5-10 mins each, all in low speed zones (ran 30-45 mph throughout except in lots.) My wife had just refilled the tank and driven home two miles--72.1 mpg indicated for that very short jaunt. The car was off for about half an hour before I took over. My first stretch was ~78 mpg indicated on the bar. It was a downhill run followed by a long flat then a few intersections. Next trip after half an hour off was accelerating vigorously through a hard left into traffic, then several intersections and a long/steep hill climb and descent. Mileage was ~50 mpg. Final leg was the long run (about 4 miles of the total) after only about 15 minutes parked/off and retraced most of the previous two trips. This had two 5 minute bars well over 50. Total for the three legs I calculated at ~63 mpg. Weather was balmy, mid 50's, and the top grill is blocked. Didn't run the heat for any of it. The ICE was primarily on for acceleration and hill climbs as well as the first minute or so after start up. Other than that the ICE was off.

So I don't find much support for the first minutes theory, except when the car is cold. I can definitely see the mileage hit when the car is left in the cold for a few hours around freezing, particularly if it is cold and humid enough that I must run the heat to keep the windows clear. That results in the ICE running much of the time.

 

Yes, in addition to short hops, it depends on how much the engine cools down between them. First thing in the am I typically get the 25 mpg for the first bar. Same thing during lunch, and after work, where there are hours between. I don't always get that low since there are several factors at work (how cold it is, where I'm driving, etc). In the summer the ICE doesn't run much at all. Regardless of exactly how low that first bar, it's consistently less than normal if enough time has lapsed.

But ... I've also stopped at a gas station, waited in line for several minutes behind 3-4 cars, then hit 78+ mpg on the way home on the first bar (3-4 miles). So it's not that "every single time you start the car for a short hop, you will have a low first-bar reading."

If you almost never have a low first-bar reading under those circumstances, all I can say is my Prius doesn't work like yours. And I am averaging 52-55 mpg per tank. Slightly less now that temps are starting to dip in NC.

 

NC Prius,

It sounds like what you are observing is specific to your drive then, because as you admit the engine cooling down is the big factor. (Perhaps you are starting off with AC high/auto in summer and heat in winter--that hurts mileage for several minutes but it isn't something I do.) If you don't cover much distance during this period such as sitting alot or slow rolling with the engine idling, then it really won't have much impact on the total tank's fuel mileage. It will also hurt if you have to do a highway/interstate acceleration during this stretch (particularly if the vehicle spent the first several minutes doing a lot of idling to warm the engine.)

It isn't the length of the drive so much, it is the warm up that is the killer. Cold weather makes warm ups more difficult and means the ICE is running more.

 

Hi Mark,

You might consider something Evan Fusco (efusco) did. He got fiberglass insulation (no backing) and put it in front of the engine , and also behind. This traps the heat in the metal of the engine block. As the car is water cooled, and your taking such short trips, there is little danger of over heating.

Even with the Prius thermos bottle for coolant, the metal still has some thermal mass. So, the gasoline it takes to warm up that metal is wasted if your car is unused for 30 minutes or more between your 5 to 10 minute hops. If you could save that heat, by the end of short series of trips you might have a well warmed up car that will turn off the engine down hill, etc.

 

I have had a similar experience in the winter to the OP. I get low 30's during the cold weather with my usual short trips. I do decent in the summer (42-47) but rarely if ever near that vaunted 50mph number. I actually suspect there are some dramatic differences from vehicle to vehicle and that with short trips, cold weather and a slightly less than top performing vehicle, along with driving which is not overly focused on mileage leads to very average results.

I drove my honda mini van to kentucky over thanksgiving and got 22 mpg for the trip. Only about 50-60% worse than I would have gotten in the prius (I've done that trip before). Notable, but frankly, I think a non-hybrid honda accord could get within 15-20% of my prius' mileage, with no efforts to increase my mileage.

I should note - I love my prius. I just wish it did even better.

 

DISCLAIMER: As the resident MPG loon, my suggestions are squarely centered in the lunatic fringe

All the comments here sound on mark. In the dead of winter a stock prius will generally have it's first 5 minute bar at about 25 mpg. Sounds like your about right. Your second 5 minute bar will be around 50 in warm weather, around 40 in cold weather.

The reason is more than just "your engine is cold". The Prius ECU (brains) the hybrid system in a kind of hobbled state until the engine gets to operating temperature. This means that your engine will always idle until you come to a complete stop for 5-10 seconds. The as soon as you move it will start idling again. The techno-bable for this is "The Stages of Prius Operation" and they spell out what temperature triggers what transition.

The bad news is that even with a block heater, you'll still have a lot of ground to cover to get to operating temp in the dead of winter. Even in the summer it takes me 7 miles to hit operating temperature (but that's a bit of a special case).

Only "fix" I could suggest is a bit more drastic than those suggested thus far. It would be 4 fold:

1. EBH - Should get you about 40-50% of the way to operating temp.
2. ScanGauge - So you can read the temperature of your block
3. EV Button - So you can have a manual override to turn the engine off when the ECU won't because your not at operating temp.
4. Learn what S4 is, and how to force it.

The trick with the EV Button is to use it to do what the ECU usually does for you. On a hot (170f) Prius, when you take your foot all the way off the gas, you stop burning gas! In a cold Prius, when you take your foot off the gas, the car idles, just like a Yaris. So with the EV button, when you take your foot off the gas, you hit the EV button (engaging EV). When you put your foot back on the gas, you hit it again (disengaging EV).

The last point about trigger S4 is not really discussed much. In order to get the ECU to trigger all the possible fuel saving behavior, you must be in Stage 4 of the "Stages of Prius Operation". Stage 4 requires more than a hot engine, it also requires that the hot engine go from running to off while at a complete stop. I've driven for 12 hours and never reached S4, so sometimes you have to force it. This usually involves pulling up to a red light and turning the engine on to let it idle off.

I know it's frustrating, but short trips + subzero block temp all translate to the worse possible Prius MPG.

11011011

 

I live in NC and yes we have had a cooler than normal november but we notcied a significant decrease in november. We pruchased the car mid Oct and first 2 - 3 tanks we were getting 48 - 50 MPG easy. Last tank barely 42mpg and this tank roughly 45. Does the cold really impact that sort of change? What is the best recommended tire pressure to operate under? Also we leave the A/C on and just use auto mode should we turn it off for winter?

 

I feel the OP's pain. I too am suffering the effects of late autumn. when obsessing I'll get in the 70mpg's during summer. my current tank after 200 miles is down to 63mpg & will likely drop to 59, unless I start taking side streets. All I can say is practice. Anyone can do it with just a moderate bit of effort.



Heck, even our Lexus AWD hybrid SUV is doing better (in the summer) than 28mpg. So don't give up!

 

No, as to either the EBH (it's made by Toyota) or grill blocking (every winter trucker would be voiding ). But of course if you left your grill block in on the way to Vegas, 115 degrees, while pulling hills at 80mph, you'd have something to worry about then. But warranty issues only apply to specific things. So if your wiper moter died (for instance), grill blocking has nothing to do with that.

 

Just did about 56 hilly miles in two trips at 28-32 F (dry and sunny), 70 mph, upper grill blocked, using low heat (blower at the #2 position.) It's been a month since I reset tire pressure and it is colder now, so the tires are running about 40/38 rather than 42/40. Mileage was right at 46 mpg or a little over. Since almost all of this was highway, normal aero losses at 70 mph dominated.

I can see the effect of the heater, though at this low setting on the highway the impact is only a few mpg. I'm still not seeing the extremely low first five minutes that some report. Typically for me the first five minutes will be in the 30-35 mpg range if the car is really cold. I do anticipate this dropping substantially when temps are in the 0-10 F range though, as I will run the heater more and it will be difficult to keep the engine warm.

 

Anyone have an answer for this part of his question?

 

I have 38,000 miles on my Prius. In warm/hot weather I get around 53-56 mpg. In colder weather, I see a drop in mileage, but not to any major extreme. Right now it is in the mid 20's - low 30's in the Chicago area and I got exactly 50 mpg on my last fillup. I drive about 16 miles to work and back which is a mixture of highway, bumper to bumper and basic local traffic.

I don't use an engine block heater or block off the engine fan. What I did do was inflate my tires to 40/38 and keep my automatic temperature control set to 66 degrees in the winter. Having the inside temp to anything higher causes excessive ICE function resulting in the ICE not turning off on idle until the car is fully warmed up.

And having a higher inside temp causes that warm up period to last longer.

I am fine at 66 degrees inside my Prius. It's still nice and toasty! Do you really need 70-72 degrees, especially with a winter coat? No...not really!