Man, my FE is going to crap, even with a full grille block and a block heater.
Temps have been in the 20s daytime and teens at night here.

Dash gauge says I'm only getting 37mpg, compared to the 45-47 I was getting a few short months ago!

Ouch...

What are other people seeing these days?

 

Suprisingly no difference in FE whatsoever in my case although the delta on the temperature is not that high either. Went from 90 to about 60F in a few months. Also I tend to do longer trips now so once the car is warmed up (which I am sure takes longer) its all good... so the longer initial warm up is not that big of a deal overall.

Though in freezing tems of 20, O_O jeez... Stay warm!

 

i went from about 37 to 31-33 in cold temps. 1/2 the time I have very short trips (when it's not my turn to drive)

 

Yesterday, with highs in the mid-teens, I got 29mpg on my 6-7 mile commute.

Today, with highs in the mid-forties, I got 35mpg.

 

I believe the Nissan Altima Hybrid is the only Nissan vehicle, which specifies 0W-20. So, the dealerships may not be familiar with this oil viscosity grade - let alone stock it.

Other Hybrid owners on this forum have reported seeing increased fuel economy with 0W-20. (see Toyota Camry Hybrid)
Toyota recommends 0W-20 over 5W-20 for newer engines: "This oil has even better fuel efficiency and cold starting performance than 5W–20." (see Toyota TSB)

If the dealership does not stock it, you can bring in your own 0W-20 and have them do the oil change.
Here is a list of API approved 0W-20: http://eolcs.api.org/FindBrandByVisc...iscosity=0W-20

0W-20 is generally synthetic (Group III base oil or higher) and is considerably more expensive than conventional oil.

 

All vehicles have an optimum operating temperature, and the colder it is, the longer it takes to get there. While modern engines make very efficient use of the fuel mixture entering the engine, they rely upon the oxygen sensor to monitor the O2 content of the exhaust, as well as sensors for manifold pressure, mass air flow, throttle position, and coolant temperature, among others.
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I purchased my Altima Hybrid in January in Upstate New York. Temperatures were in the teens and 20's for most of two months and I averaged about 27 MPG. Now that we've thawed (40's day, 20's night), I'm running about 32 MPG. I have about 3 miles city and 8 miles highway driving each way on my commute. It's just cold batteries aren't as efficient as warm batteries.

 

Temperature has made a HUGE difference for me. For the tanks with the coldest temps (10degrees ave.), I was getting no better than 34mpg. As soon as temps got up into the 30s, I saw my mileage get up to 36mpg. Now, with temps in the 40s and 50s, I'm getting close to 40mpg again. These are all calculated numbers, not dash readings (which are always high).

BTW, I have a block heater and a full radiator block and I still got relatively crappy numbers when it was frigid.