Really bad mileage on 6 hr drive

<div class='quotetop'>QUOTE(nstevens @ Dec 6 2006, 04:31 PM) [snapback]358643[/snapback]</div>

Cold weather can effect the MPG you get, but if you were driving highway, the engine would have heated up in time to not really affect it. For me, the cold weather (28 F today) affects my MPG more with local, city driving vs. highway, but once it heats up its fine (unless you use the heat on high in the car, then the ICE seems to want to kick in alot more).

Seems to me you need to slow it down - doing 78 mph will not help your MPG at all. try cruise control at 65 - 75. If you have to drive that fast, expect lower mileage. Doubt it has anything to do with being rear ended, unless the tires are out of line or something (if thats possible) and you have more friction than normal.

 

<div class='quotetop'>QUOTE(Orf @ Dec 6 2006, 04:39 AM) [snapback]358663[/snapback]</div>

One thing they add is more oxygenates. In the past that was MTBE, but for environmental reasons, as most of us know, that additive has fallen from favor. Oxygenates reduce emissions in colder weather, but they also reduce the energy content of the fuel - so you have to burn more. The winter blend is formulated to evaporate more readily.

Engines don't run as efficiently in the winter. Air density is a lower lower when it is 80F outside than when it's 18F. Denser cold air means the mixture has to be enriched. That itself may not account for a 25% in mileage, but combine with fact the fuel has less energy, it could add up to 25%. You engine also has to work a bit hard to keep the emissions control system at proper operating temps.

Talk to freinds with SUVs (do you have any? ) I used to see a 3-4 mpg drop on my Ford Explorer when CA would switch to winter gas* and the temps went down. 3-4 mpg doesn't sound as severe as your drop - but as a percentage it's about the same. That is something that we always need to remember about the Prius - there are normal conditions that will swing the mileage of all cars up or down. But when you get 45-60 mpg, a 10%-25% swing LOOK much bigger.

(*Note that in the last several years, summer gas in CA sucks as bad as winter gas when it comes to mileage.)

Note another weather factor that may change in the winter. Wind. I make trips north on I-5 regularly and find wind has a big effect on both my cars (I usually take the Chrylser on the longer family road trip). When there is a stiff north winter wind coming down the freeway, I will see big differences in the mileage between going northbound and southbound.

 

<div class='quotetop'>QUOTE(savegreenbacks @ Dec 8 2006, 11:11 AM) [snapback]359269[/snapback]</div>

Your first paragraph is what worries me. It was actually quite sunny outside, so I rarely even had the heater on. I've driven on long summer trips before in my '05 Prius at 80 mph and got 48 mpg. If the cold weather doesn't have a big affect on long freeway mpgs, then why did I see a 16mpg drop? That brings me back to my original concern that something besides mph, but still within my realm of control is at fault ... either a bad oil change, or something happened when I got rear ended. I don't really think its the wind, since it was blowing around the same speed and direction both to and from (and I didn't see a gain/drop of mpgs for either direction) . If 32mpg is normal for 6 hours at 80mpg and 18F, then I'm not concerned and can live with it.

On a side note, driving 65 on these freeways would be like driving 15 in a 30 zone. They are long-haul straight as an arrow, flat as a board freeways with nothing to see for hundreds of miles. I'd rather not be the guy in the hybrid getting passed by Semis every 30 seconds.

 

When I first bought my 2005 Prius, I took a trip to Chicago and back from Denver, I got 42 on the way out and 34 on the way back. Of course, it turned out that I was combining all the worst possible
factors in the trip, especially on the way back.

1. I had put Blizzak tires on, very soft rubber hurts mileage.
2. High Speeds (75 to 80 for much of the trip)
3. Very Cold (0f to 15f most of the trip)
4. Elevation change of about 5000 feet
5. Heavy crosswinds. Crosswinds are almost as much of a mpg killer as headwinds.
6. Snowstorm. Driving through slush really hurts mpg

Most of the time my highway mileage is in the 48 to 52 range, so clearly these factors make a big deal. Did any of these factors come into play on your trip besides the speed and the temps?

 

<div class='quotetop'>QUOTE(Curtis SAC @ Dec 8 2006, 04:25 PM) [snapback]359461[/snapback]</div>

This lessens my worries, but I went from 48 mpg down to 32 mpg which ends up being a 33% drop in mileage. Hasn't anybody on this forum ever driven for 6 hours straight at 80mph in really cold weather?

 

Ha. My first post. I've learned so much from this forum and now I can contribute something. Last weekend, I drove from Madison, WI to northern Illinois. It's 2 hours each way. I set the cruise at 72 on the way down and the temperature was 16F; on the way back, I set it at 69 and the temperature was 10F. The MFD said 43 mpg.

btw, I got my black 2007 on 9/30 and I love it. I've driven crappy cars for 20 years and I still can't believe that I get to drive this car where ever I want.

 

I did a 4 hour E-W and return on I-90 (flat) in S Minn a week ago, Going West, = 38 mpg, 18F , wind 5-10 NW or slight/light quartering headwind, cruise at 65 MPH. Return a day later = 50 MPG, 35F, calm to 5 mph west tailwind, cruise at 70. As you say boring, so was playing w/ cruise and checking display mpg, under those conditions (fairly steady state) 2mph speed delta = 1 mpg delta, this would not be linear of course. However my trip reflects what you experienced w/ colder temps and highway speeds, maybe check with the weather channel for trip planning .

 

<div class='quotetop'>QUOTE(Subversive @ Dec 7 2006, 01:45 PM) [snapback]358953[/snapback]</div>

Oh, good, it's not just me. Since my last fill-up a couple of weeks ago, I've been mostly going on very short trips (10 minutes or less). This evening I went on a longer trip (about a half hour) and my MPG finally shot above 35 MPG at 150 miles on the tank (and that was with the heat on, but when it's 15 degrees like it was today, I'm going to keep that heat on, thank you very much).

 

<div class='quotetop'>QUOTE(nstevens @ Dec 8 2006, 04:44 PM) [snapback]359471[/snapback]</div>

My wife and I drove from Chicago to Kansas City and back over Thanksgiving at 80 mph and got about 43 mpg the whole way.