Cold Weather Mileage

My own limited experience:

Bought my Prius in June and was averaging 46-48 mpg all the way through October with the 48 being in October itself.

Then November hit and started going down. Since then Im around 42-44 mpg I think mainly due to use of the heat now.

 

So you actually switch to Neutral while driving from drive and back? If so what is the difference b/t this and just taking your foot off the accelerator and having the engine shut off?

 

I love cold weather mileage

Maybe this will cheer you up on the east cost, my mileage changes by 10 mpg from summer to winter. I get an average of 36 mpg summer and 46 mpg in the winter. How ever hard is on the gas mileage using the heater it is even worse using the AC, especially in a city like Phoenix when it runs all the time. The best mileage I ever got was 52 mpg on road trips during the summer (in the cooler mountains NE of Phoenix)

 

Part of his point is that the ICE won't shut off during this early warmup period. It insists on running to warm itself and the catalytic converter until after a minute+. So if your route allows coasting, next best is to let it coast in neutral.

 

I have a 07 with 6500 miles. After reading the posts here, I know that cold weather does cause a drop in mileage, but I'm wondering if I have other problems. Most of my commute is done at highway speeds, 30 miles each way. 1 block from my house, I'm on a 55mph road, then to the Long Island Expressway HOV lane, where I usually do 65-70 (any less & I'd probably be shot). I'm not trying to get very high mileage, and was getting around 43 mpg for the 1st 5000 miles, which I was happy with. The last few weeks (where the temp has dropped) I am down to 35mpg. I keep reading about people doing 46+ with similar driving & wonder if it's something about my car, or should I be happy with what I have.

 

One of the other reasons that the mileage would drop is the winter blend of gas...

 

can anyone describe what the difference between winter and summer gas is? and when the switch is made?

 

Gasoline Blends in the US are a crazy-quilt of regulations, so you need to figure out when changes take place for your locality, and in fact in some cases the blend requirements and schedule can vary with a few miles of each other. That's something that contributes to the cost of Gasoline, when refiners have to make multiple blends at multiple times and can't ship one to another location if there's a shortage of that type.

But, in general, there really isn't a "Winter Blend" of gasoline. It's more accurate to talk about the "Summer Blend" because that's the one that's mandated.

Basically, gasoline is made of volatile components, which means they evaporate or dissolve in air.

In the summer, which is generally warmer, the components evaporate more quickly which leads to more volatiles getting into the air unburned. They then react with other things in the air to make smog, particularly ozone. The measure of this tendency to evaporate is the "RVP" of the fuel. Higher RVP is more volatile.

In some high pollution areas, gasoline is required to be less volatile in the summer (generally defined as June 1 - Sept 15) to reduce this pollution.

I know there are at least 12 of these areas (LA, New York, Atlanta, etc).

In addition at least 15 states have their own blend rules on top of the EPA rules which can change the blends and the definitions of 'summer' when you cross the state line. For instance last time I checked California law says 'summer' begins in May, at least for Gasoline Refiners.

Before you ask, you can't use the same blend all year round because the summer blend doesn't combust as well when it gets really cold.

Winter fuel is generally cheaper than Summer fuel because it can contain more volatile components which means a little less work refining.

Wanna hear something funny about Ethanol?

Ethanol is pretty volatile, so using Ethanol as the Oxygenate in fact increases the RVP of fuel and makes it more likely to cause smog.

But, for political reasons, there is a waiver of the Summer Fuel Blend RVP to allow more Ethanol in the mix even though it defeats the purpose of the Summer Blend.

Since California started using Ethanol in Summer Fuel, smog has gone up.

 

I normally get 48-52 real mpg, despite what the computer says, here in northern Utah. Last two tanks, since weather turned cold was 43.7 and 41.9 MPGs. Outdoor temps during driving have been in the 30s F mostly, sometimes in low 40s. Tire pressure is still 40 front/38 rear. No driving in snow nor ice, just cold temps. I'm experiencing worse drop offs than the ~2 MPG others report. Car is still young for an '05; still about 14.4K miles old. Could my huge drop off in fuel efficiency be due to temps, altitude, need for oil change (last one at 10.5K), or something else?

 

Curious what you means by "real mpg, despite what the computer says". It seems that the majority of milage loggers in here (the hardcore Excel spreadsheet guys) feel the MFD is within +-1.5mpg of hand calculations when calculated over a large sample. Do you feel this is inaccurate and why?

As for cold weather milage, I used to be happy to get 44mpg when I had the 17" wheels and sticky tires. With some careful driving and a swap back to stock rims/tires I am not averaging 52.5mpg over the last 5 tanks or so. Temps are in the high 30s to low 50s.

 

Same Problem

I have the same issue I am driving from SE Pa to Atlantic City 5 days/wk. 160 miles/trip. The temp has 20's and low 30's prior to that whe it was warmer I was getting on average 45-46 mpg, now I this morning 41.9 mpg. I can't imagine I am doing anything wrong driving wise and even slowed down to 70mph. I was thinking of increasing the psi in the tires to 42/40 and hope that may helped as others have suggested.
Not sure what else that I can do at this point except be happy I get over 40 mpg.

 

Have you factored in a rise in barometric pressure, dew point change, or extra wind? All of these are what affect our milage for the same reasons as temperature, they increase air density and thus resistance. Temp has the added insult of keeping our engines too cold too.

 

I've been in the 51 to 53 range since I got my Prius in March.
I've got a good commute: 25 minutes, some interstate, some city, and one 5 minute section of 75-100 mpg on the ride home. I'm still hanging in there at 50 right now. We've had really cold weather, but I've blocked the upper grill and have the engine block heater. I can't plug in at work for the EBH though. I'm barely holding on to that 50, and it's just a matter of time before it goes to the forties.

My driving has changed since I got the Prius in a lot of ways. One, with the cold weather, is thinking about whether I really need to make a trip out or not, particularyl short trips. I hate to see my mileage drop at all, and so I don't just get in the car at the first whim. I actually think about it. Amazing how my behavior changed when I can see the results on the MFD.

 

Still beats all others

Running 16's with agressive directional Winter BF Goodrich Snow tires. Also have Thule roof ski box on top. Was down to 33mph. Started using the EBH and blocked front intakes with pipe insulation. Now back up to 38+. Drove thru winter storm with 6 + inches on ground and went around everything. It does move around in heavy wind with box on roof. Woo Hoo at 38+ in winter upstate NY

 

voi9, the mpg of the white Prius (grill not blocked) at the office has dropped below 50mpg since the cold arrived. I've been running fully blocked and am just barely keeping 55mpg on the MFD this tank. Once the ICE is warmed up (sometime after 5-10 minutes) I set the temp somewhere in the low 70's, turn the fan on low, auto off, and use the upper vents to direct the hot air over my hands.

 

Beating the Cold

Today's round-trip commute - average of 58.6 mpg over 97 miles. Temps in the 40's this morning, high 30's coming home this evening. It can be done!

Yesterday I filled up with 89 octane as opposed to the usual 87, as the 87 pump was out of order. I'm wondering if that helped. Usually I'm getting low to mid 50's for mpg's at these temps for this commute. Other than that, I'm doing all the usual good stuff - grill blocked, 42/40 psi, EBH (although I didn't use it today), EV button on approaching stop lights, taking full advantage of gravitational assist on the downhills, only braking to avoid an otherwise imminent collision, etc, etc, etc.

Pics of MFD should be attached.