Why my mpg does not match promised values?

Better for a Barbeque:


I don't like the heat of summer - next Friday predicted 37C max.

I prefer our winters to our summers - temps sorta 10-15C min, 18-25C max. Just perfect!!! Winter might occasionally get down to zero - every 4 or 5 years!! And I've never seen snow - apart from a mountain top about 20 km from where I was touring.

 

Colder air is simply denser air. This affects 4th gen, 3rd gen, 2nd gen and every other car, be it electric, hybrid, or pure ICE.

 

I guess what I'm trying to say: besides the physical effects of winter temperatures on the engine efficiency, the computers intentionally change the programming when they read those lower ambient temperatures, when temperatures get below some threshold.

 

i have a 16 two , gets 50MPG + regularly , only in the winter months or cold does does it get 49 mpg , drive 250 miles round trip have just over 170,000 miles on it

 

Denser air certainly is a factor but I think there are several major factors on a hybrid and even more so with a EV (you probably know where I'm heading).

NiMH batteries supposedly don't lose as much capacity as the Li batteries in the cold but compared to my 2016 Prius which was NiMH and the 2013 Prius C I had, they lose enough. This means the ICE will spend more time running not just to heat the cabin but to charge the battery. Plus battery output is limited in the cold, same with brake regen. Tesla owners, Leaf owners see a huge drop in range, of course that's not just because of the drop in capacity, but also how EV's heat the cabin...so they get an extra penalty. Overall, the battery stuff is probably the biggest contributor in drop in fuel economy. For me in my Prime I was getting almost 200 MPG round trip to work I'll do good to get about 100 MPG today (it's 16 F this morning). When I had my Dodge and other ICE vehicles, sure I would see a drop in fuel economy but it was less dramatic, like 26 MPG to 24 MPG.

The next thing I think makes a difference is the tires and the more dense air. Surely I'm not the only one who notices that their Prius doesn't quite coast down hill as fast on a cold day versus the summer? Hills I would normally hit 70 MPH now more like 64-65 MPH, maybe it's just me.

Finally, I think the Prius being the most efficient car one the road (both as a hybrid and EV) I think external factors are going to be more noticeable. By most efficient, there aren't any other cars that get better fuel economy and the Prime, many folks are getting 4.5+ miles per kWh.

 

Absolutely! There are a number of factors. Denser air is a big one, but as you said, not the only one.
Wouldn't batteries loosing capacity would not affect efficiency, only range?

Tires are a factor, but not so much due to denser air, but different road conditions. Cold rubber behaves differently, and snow and ice and even rain requires more energy.

Short trips in winter will also affect ICE vehicles just as much as EVs.

If measured, any car will loose about 20% efficiency in the winter (0-20 degrees). As you said, it is more noticeable with more efficient cars. And especially noticeable with BEVs as that efficiency is expressed in range.

With BEVs you have the added loss in creating heat. This makes the average range loss for BEVs more like 30%.

 

It was below 0 Deg. F. pretty much all day today and wind chills were consistently around -20 Deg. F. or so. So, today was a good test of the car's winter driving characteristics and performance. I really couldn't be much more satisfied with it as I had no trouble with it starting, heating the cabin, sipping gas (just over 50 mpg indicated), or any other trait. Even with the brutal temperatures today, the car was quite efficient.

 

Hit 30K miles today on wife's 2016 Prius 4. Odometer reads 62mpg average for that duration.

SM-N960U1 ?

 

Very impressive

 

Trust me, it would have been better if I was the sole driver for all those miles. Wife generally exceeds the speed limit on the freeways whilst I generally go approx 5mph below in the left lane at approx 65mph. Plus the usual keeping it in the zone in regular roads. I take off at traffic lights like a snail.

SM-N960U1 ?

 

Oops I meant to say I ride the right lane. Hahah

SM-N960U1 ?

 

The Florida flatness certainly helps...

 

I'm sure the relatively warm temperatures in Florida compared to NE Ohio have a lot to do with it also. I have no trouble averaging above 60 MPG here as long as I don't need any cabin heat.

 

On my 2018 prius 2 I always get low mpg when it colder out and a cold engine. We're talking 45 cold vs 60 mpg when warmed up. On a warm day with engine warmed up in the country going about 40 mph I can get 70+ easily.

 

Are the official MPG ratings measured with a certain number of people (or weights simulating people) in the car? It seems like that could make a big difference.

 

I don't believe so, the older type definitely didn't - they're done in a laboratory setting, and putting 5 people in the car would have no effect.

The new WLTP test doesn't seem to either.
What is WLTP: the Worldwide Harmonised Light Vehicle Test Procedure? | WLTPfacts.eu

As with the old test, it's very subjective - NOBODY will replicate it in real life - as no 2 drivers drive the same, no 2 cars are loaded the same on identical repeatable trips. Even the same driver will easily have 10% variance on the same trip with similar traffic conditions 2 days apart.

My wife drove similarly to me, similar acceleration rates, similar speed on the highway, but I mostly averaged a little better - it had to be something to do with a combination of little factors, and mechanical "thinking" through what was happening, maybe easing off the throttle a little earlier before stops, or as I crested a hill - I couldn't feel the difference, but it was there.

The key to remember is - if I consistently used ~30% more than the NEDC test result in, say a YARIS, I'd likely still use ~30% more in a LandCruiser. It's not cut in stone, though - some cars are easier to better the NEDC result (diesels in particular) than others.

 

How Vehicles Are Tested

Detailed Test Information

 

That's the old test.

This is the new one:

What is WLTP: the Worldwide Harmonised Light Vehicle Test Procedure? | WLTPfacts.eu

 

No, Prodigy's links are to the U.S. tests, updated to at least 2017. Your links are to the EU tests, also to 2017+.

 

The US always tends to do their own thing. Who else measures fuel in US gallons?

Even when Canada quotes mpg they convert to imperial gallons first.