Significant Drop in Gas Mileage

You don't KNOW that for sure.
All you really know is that you are going to the same station and using the same pump(s).

 

IIRC, the Prius v has a small drum brake incorporated in the rear disk brake, for parking brake. That would eliminate one potential brake drag issue (the regular 3rd gen Prius with it's parking brake incorporated into the disk brake, prone to drag if misassembled) .

But yeah, just for giggles: chock the front wheels, raise the rear, release the parking brake, and make sure both rear wheels spin semi-freely. This is "low-hanging fruit", something that can be done relatively easily, and a variable that should be checked, even if it's just to be dismissed.

 

If it get's back to displayed high 4's in summer, I would write it off as seasonal variations, and acceptable. If not, then I'd start digging.

BTW, your displayed very likely is a little worse (lower) than calculated. Toyota is notorious for exaggerating the display, anywhere between 3 and 10 percent, depending on the vehicle. Our 3rd gen Prius has displayed fuel economy 7.5 percent optimistic, with well over 100 calculated tanks.

I think what you need is for more Torontonian Prius v owners to chime in, regarding their winter mpg. I suspect it's not far out of line, but not sure. Have a look at this, the median fuel economy (calculated) being reported by other owners, and this is all over the map, not in a cold winter clime like Toronto.

Very few are getting 4.5, judging from Fuelly:

Toyota Prius V MPG - Actual MPG from 890 Toyota Prius V owners

A screen grab from above:

 

Here is a troubleshooting list of MPG killers, covering almost all the usual suspects except sticking brake pads/pistons/calipers:
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

Please review it to see if any topics have been missed.

Fresh new tires will typically increase fuel consumption a bit until they are broken in.

Driving & skiing in BC and Alberta the past two weeks, I noticed that fuel stations had different patterns of ethanol vs octane rating. Some stations were labeled as having 10% ethanol in all grades, while others were labeled for 10% in #87, 5% in #89, and 0% in #91. So if your supplier has recently changed patterns and the 91 Octane shifted from 0% to 10%, this would be expected to change your fuel consumption, though only by a few percent.

I would not blindly trust them to catch brake pads that have started to drag or calipers that have frozen from corrosion, especially if you live in an area where road crews love to use salt or brine in the winter. This has now caused me problems on two past cars, as local government policy forced increased salt use and auto mechanics had not yet caught up.

 

Stop & go from traffic lights affect mileage too, especially at higher speed intersections.. I assume your husband is traveling toward Metropolitan Toronto.

 

You don't have to mess with them, but as I said, just raising the rear of the vehicle, releasing the parking brake, and spinning the wheel, is low hanging fruit.

Even simpler: directly after an extended drive, feel each wheel. If any are inordinately hot, that would likely be due to brake drag.

As likely as not your problem (if any) is not brake drag, but if you're semi-serious, it's an easily checked variable.

For me the elephant in the room is that Fuelly chart. I'm not sure you can filter it to be Torontonians only, though there likely are a few. The majority I would think are from the States, and likely with milder winters. Again, these are calculated tanks. It could be a few fluke good tanks at the outset? Because if you look at the median in the chart, you're in the middle of the pack.

 

Another thought: is it still on the original 12 volt battery? They're good for 4~5 years, and might be a factor, though a long shot. A dying battery may make the engine run more.

 

He has a lot more confidence in the dealership than I've ever had in even my best independent shops.

If he won't check, them you can check this yourself within a few minutes after he gets home some day.

 

With sustained higher speed driving, the engine won't do any shut down. If you check the stats, the car does better around town then on the highway:

Fuel consumption ratings search tool - conventional vehicles | Natural Resources Canada

Snapshot from above:



The threshold for engine turning off is around 72~74 kms per hour, fwiw. And that is instrumental in achieving the better numbers. Around town the car shines, especially if you abide by speed limits, keep a good following distance, coast up to slow downs, and so on.

This is at odds with the current canadian fuel consumption stats (snapshot above). I know they've changed the testing method in the last few years, to bring it closer to reality. And even then, those are in ideal conditions. Fuelly stats are the reality for the car.

 

I work only 3 miles from my house. During the winter, this barely gets the engine warmed up. Mileage is 8 miles per gallon less (40mpg) than when I jump on the freeway to someplace. Then it soars up to 50mpg!

 

I think that is why my salesman with his Gen 1 Prius walks to work at times. I believe he said his commute is about 1 mile.

 

OP has long commute, but also sustained high speed 100~110 km/hr. And it's a Prius v.

I'm trying my durndest with our regular Prius (albeit with 17" rims, a real mix of trip lengths), and my fuelly icon's at 4.9 liters/100 km. OP wants a Prius v to return to sub 5, in TO, in winter...

 

A confession.

I too have a '12 v.

In the beginning, I was getting MPG better than I am now. Only by 3%. Why? Because the long miles trips I took back then I was obsessive about doing 4-5 MPH under the speed limit. Gradually, I got less obsessed. Today's trip to the grandkids I left a bit late and did 1 or 2 MPH over the speed limit. Slower than 95% of the huge things that were passing me but enough to affect my MPG. So my average has slumped. Even though my tires are pumped harder than they were and there are no other changes.

Just the habits of the driver critter.

I track my MPG using fuelly so I can see seasonal or equipment changes. I still get EPA figures on average, just not as robust.

(Checked the air filter lately? Still running the HVAC on Auto? Looked at the degree days for the affected period? Still using ECO mode? Any change in cruise control use? )

 

My son was hoping his 2015 Prius v would get about the same mileage as the 2005 Prius he had earlier. I think the Prius v ended up being a little lower.