Tickled Pink

You bought your Prius around the same time I bought mine. (Yearly Cycle)

Kind of a "Neat" time to buy a hybrid, because as Winter ends and Spring turns to Summer you get to watch the "natural" improvement of your gas mileage as temperatures warm up.

Be fore warned, the opposite affect will manifest as temperatures drop with approaching Fall and Winter.

But IMO it's kind of a "Fun" yearly thing, to watch your gas mileage improve as skies clear.

I've adopted a "Game Of Thrones" approach. Which is to mean, I enjoy the Spring, Summer and even Late Fall, 50 mpg gallon tanks. But every time I fill up during The Fall,- I say to myself "Winter is Coming".

 

Maybe it's me, but my MPG track indicates low points in Summer and Winter (worse in winter) with max MPG in Spring and Fall. I attribute it to temperature extremes taxing the motor for more power (A/C drain on battery means ICE kicks in to maintain charge in summer and the drain on coolant heat means ICE kicks in to maintain heat source in winter). Spring and Fall take the max advantage of naturally cool air for riding in A/C comfort for little gas/power.

 

There may be some untested loads showing up at temperatures above 85-90F. I've acclimated myself to the Alabama summer heat but noticed with our 2010 Prius, there was a distinct MPG drop without the AC in the 85-90F range. I had seen this before with our 2003 Prius but also had thought it was the AC.

One clue, the engine coolant that normally runs in the 84C range was running 90C that day. It suggests that in high ambient temperatures, the engine may be running more to keep it cool. My speculation is when the engine coolant shows 90C, the control laws want to run the engine to circulate the coolant even though it has an electric water pump. If the electric water pump is operating in 'virtual belt mode,' it would explain the extra engine run time.

The reason I brought this up is I was on one of my benchmark routes in the heat and had recorded a significantly better MPG just a couple of days earlier in cooler termperature. But I was not in 'benchmark' mode and had other chores to run. Not to worry, Global Warming is coming and I'll have lots of opportunity to investigate this higher temperatures vs MPG relationship.

Bob Wilson

 

there is no question AC lowers MPG. in a city commute i get 55 MPG with AC and 60 without. I'm sure hwy difference is much smaller though. to compare, i struggle to get 50 MPG when really cold.

 

there is another explanation for what you see. when battery is hotter, maybe ICE runs more to spare the battery?
did you monitor HV battery temps?

 

The Northwest has pretty moderate summers. Not really a lot of "Scorchers". But during the summer I run in ECO, and that has been my experience. I've been pleasantly surprised at how well the AC seems to work, and really how little impact it seems to have on my overall MPG's.

For those few days one would call "Scorchers".....I'll stop using ECO and just crank the AC.

I'll trade a few short periods of less than optimal MPG's for the luxury of comfortable driving.

But then again, I'm lucky enough to live in an environment where those days are pretty limited.