Really bad mileage on 6 hr drive

<div class='quotetop'>QUOTE(Grandma Judy @ Dec 6 2006, 05:38 PM) [snapback]358649[/snapback]</div>

I realize I won't get optimal gas mileage at 80 mph, but I've made other trips in the summer and averaged in the high 40s mpg, so I guess it must just be the cold weather.

<div class='quotetop'>QUOTE(tumbleweed @ Dec 6 2006, 05:57 PM) [snapback]358662[/snapback]</div>

Yes, I filled my tires to 40 right before I left on the trip.

 

I drove from NW Ohio to north of Chicago last Thursday - the temp dropped from 63 degrees to 28 degrees at my destination. Winds were from the SW. Drove 6 hrs (about 340 miles). Tires at 38/36. Got 42 mpg. On my return trip Sunday average 48 mpg.

 

I would say cold weather is probably one of the biggest factors in my gas mileage. I did a two hour drive a couple weeks ago and the temps had dropped into the low 20's, and it was VERY windy. These two factors brought my mileage down to around 38MPG for the trip, but I was only going 70 mph. The ICE has to run more in general, just to keep the engine warm, not just the first few minutes. When it gets really cold here in January and February, my tank averages always drop into the 30's and I notice that the ICE continues to run at stop lights.

My Prius seems happiest (gets the best MPG's) when the temp is between 65F and 75F. (Probably explains why the southern Cal folks can easily get over 50 mpg on every tank.)

Luta
Where the current outside temp is 20F

 

I have a 2006 Prius and recently got rear-ended on the freeway. I'm in the process of getting the bumper repaired (apparently the only damage was to the bumper), but I did take the car on a 6 hour trip last weekend. The temp was cold, around 18 F on average and I was probably averaging around 78 mph. I averaged only 32 mpg. I was under the impression that the cold weather had a larger effect on short trips while the engine needed to warm up. I was suprised that I only got 32 mpg on such a long trip.

In comparison, I took my 2005 Prius on a roadtrip this summer (80 F outside) and averaged around 49 mpg on a 5 hour trip at around 80 mph.

Is it normal to only get the 32 mpg on a long drive in cold weather? I'm extra paranoid right now since I'm worried that getting rear ended may have damaged something else with the car. I've called two Toyota dealers and they both told me I should just take it to the body shop since it was just a rear-end accident.

 

I'd assume that a Prius would get much worse mileage at 78 mph than at 55 mph - could that be part of the problem? (I have yet to put any gas in my 2007 Prius since I've only had it a week.)

 

Under the circumstances you mentioned 32 MPG may be about normal. I get about 47 or 48 MPG at 70 MPH on the freeway in the summer, light traffic, using the cruise control, no stops just going down the freeway with no headwind tires inflated to 44 lbs. In cooler weather with a headwind I have gotten in the high 30s at 65 MPH. I think the low temperatures don't have as much effect at freeway speeds as they do around town but they must have some, and the winter gas has a lot of effect. Also cold temperatures drop the tire pressures, did you check your tires at 18 degrees?

 

78MPH is also a factor. 55 to 65 obtains good mileage. I track all fillups and have noticed originally when I first got the car I was getting stellar mileage. Back then I was preoccupied with getting the best mileage. As I got used to the car my old driving habits came back (speeding, punching the pedal, slamming the brake, following too close, etc.) which really impacted my mileage. It's 35-38F where I live and if I drive "right" I get 48 to 51 per the MFD. If I drive poorly I will get 40- 41.
Food for thought....
-b

 

<div class='quotetop'>QUOTE(nstevens @ Dec 6 2006, 02:23 AM) [snapback]358686[/snapback]</div>

Where do you drive, averaging 80mph and not get stopped for speeding??

 

At that speed, in 35-40 degree F weather, I have been getting around 40-45 MPG. Your mileage seems pretty low, even for that colder MN weather (18 F). I have never driven a long trip in those temps.

Check for bent panels near the damaged part of your car. If a piece of bumper is sticking out, that could cause an increase in drag (air resistance).

You might as well take your car to your dealer if the mileage doesn't normalize soon. Something may be wrong.

 

<div class='quotetop'>QUOTE(autoxic @ Dec 6 2006, 07:45 PM) [snapback]358729[/snapback]</div>

I'd forgotten about him being rear ended.

As you suggested, anything that increases drag is going to affect mileage.
If the drag coefficient deviates much from the 0.26 in the design, it could have a notable effect at higher speeds. After all, drag force does vary as the square of the speed. About twice as much drag at 78 mph as at 55 mph.

Dave M.

 

I'm betting his tires were really low. The difference between 80 degree and 18 degree weather could result in a swing of 6 or 7 PSI. If the tires were low to begin with, then you could be down in the mid 20's at 18 degrees.

 

On my 2006 I have had a drop from around 52/54 on highways miles to around 47. The problem is: low tire pressure. The idiot light came on and the pressure read 25psi! I reinflated the tires and mileage is back around 52. B)

 

<div class='quotetop'>QUOTE(Orf @ Dec 6 2006, 01:39 AM) [snapback]358663[/snapback]</div>

Yes they do, at least in states where there is fairly cold winter temperatures. I do not know chemically what they put in or how it works but it's function is to decrease pollution by helping the gasoline burn better when cold. From my own experience and posts on this site from last winter I think in the Prius it costs us about 5 or 6 MPG (I'll let you do the math to convert to liters and Km).

 

This summer we went on a trip across the country and got the worst mileage ever. All through the midwest I got only 38-42. So I believe your low mileage is not unusual. Through in cold weather, very high speeds, add a headwind and a uphill grade and there u go. Makes you want Spring to come LOL.

 

<div class='quotetop'>QUOTE(Marlin @ Dec 7 2006, 08:44 AM) [snapback]358797[/snapback]</div>

Nope, I took my cold car out of my garage and went to fill the tank and tires at a gas station less than 6 blocks from my house. The tires were cold and I inflated to around 40 psi.

<div class='quotetop'>QUOTE(autoxic @ Dec 6 2006, 11:45 PM) [snapback]358729[/snapback]</div>

Yeah, even though I've been told by two dealers not to, I'm going to bring it in after the bumper is fixed to have them check it out. I don't think its a drag problem .. the bumper is basically perfect except for some small crumples and cracks in the middle (nothing is popped out or bent out of place or anything). I also recently got my oil changed ... could that have screwed something up? I've heard overfills can cause mpg to suffer?

 

The culprit, as many people have pointed out, is likely the high speed combined with winter grade of gas. Cold does effect it, and if you were running the heater at the time to keep the cabin warm, that would have lowered your mileage too.

 

<div class='quotetop'>QUOTE(derk @ Dec 6 2006, 11:35 PM) [snapback]358725[/snapback]</div>

Driving from Minneapolis to Omaha and back. Super flat, super boring, 70 mph speed limit for most of the trip. Couldn't help but push 80 mph

 

32 mpg sounds a little low to me. I'm in Massachusetts, it gets cold here too, and my 2006 gets about 39 mpg total, due to half of my driving being Masspike and I-495 at 79 mph (cops in Massachusetts won't hassle you, even when set up with a speed trap, unless you are going ten over the limit or fifteen over on the freeway, unless you are driving unsafely--you should probably slow down around pedestrian areas, school zones, and "speeding limit strictly enforced" signs). And that's with air on, headlights, music, and low pressure in the tires. But I'd hold off a bit before making a final judgement, maybe see how your next tank of gas does.

 

<div class='quotetop'>QUOTE(nstevens @ Dec 7 2006, 01:23 PM) [snapback]358923[/snapback]</div>

Someone else on here recently had a Quicky Lube use a higher viscosity oil, and their mileage dropped significantly. Do you know for sure what they used. Have you had the alignment checked since the accident? If everything else is fine, I'd suspect headwinds.