Fuel mileage in the toilet now that winter is here

The heater magic numbers for the GenIII to not make the ICE go on (too much) at stops is 68 degrees or less, and fan on two bars or less. Don't turn either defrosts or the seat heater on.

 

Hehe. At those temps, the ICE will run as much as it wants to. The heater magic numbers would probably not work for you until the engine coolant and battery temps rise to max, and the hybrid battery is near full charge, which takes quite a while at 10F or less. It was -9F here last night. All I hope for then is that the car actually starts.

 

During September with moderate temperatures in Connecticut, my daily average for 10 miles each way to and from work was 64.5 mpg as indicated by the MFD on my 2013 Prius C. During November, the average dropped to 55.2 mpg with a mean temperature of 42F during the round trip. So far during December the MFD is indicating 50.5 mpg with a mean temperature of 33F and one 12 minute warmup in the driveway to remove ice from the windshield. Yesterday and today the mean temperature was 20F and the mileage was 47.1 mpg. I'm recording my daily trip statistics over the course of a year.

 

Yerp. I average 56mpg. (61 hypermiling and 72record!). And....43 at the moment. Its frustrating because I just put new tires on it, filled up twice now at unfamiliar gas stations. Between those and winter addatives I just cant tell what has caused tbe change. It had been driven so little recently that i likely got "cold gas" after most others and i could have been these last two.

 

Aside from the many reasons usually mentioned, such as longer warmup time and ethanol in the gasoline, there is a fundamental reason why fuel economy decreases during the winter. As the ambient temperature gets colder, the temperature difference between the combusted gas in the cylinder and the air outside of the engine block increases. This causes a higher rate of heat transfer from the combustion gas through the cylinder wall and into the atmosphere thus reducing the temperature of the combustion gas at any point during the expansion stroke as compared to warm ambient conditions. The reduced cylinder gas temperature means there is less thermal energy in the combustion gas and less energy to be converted to useful work per unit of burned gasoline. So the ratio of useful work to fuel burned is smaller and the fuel mileage is lower.

 

^Sealing the gaps between the hood and fender can help hold in the engine bay heat. I use foam pipe insulation pieces for this, pushed onto a convenient crimped flange along the seam.

 

I'm not sure how the mileage would change with warming up before the trip vs warming up during the trip. However "The ICE will warm just as fast when driving it versus remote start..." doesn't make sense because there is much less air flow when stopped than when moving even with grill blocking. That's why grill blocking works.

 

I guess I assumed an ICE will warm up faster when under load versus idling? Maybe I'm wrong....

 

ECO mode accomplishes the same thing, no need to mess with the heater.

It drops the coolant threshold from 145°F to 114°F in the regular Prius. In the plug-in model with a fully warmed system, it allows the engine to stay off while still providing heat all the way down to 87°F.

Get an aftermarket gauge. You'd be surprised by discoveries like that. The design is well thought out.

 

"ECO mode accomplishes the same thing, no need to mess with the heater."
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Never thought of that, but then again I don't use ECO mode. I'll try it over the next couple days to see how it works for me. Thanks!

 

I guess I don't get what you are saying. When I'm using the heat (at 65) the ICE will still run when I'm stopped in EV.

 

Until coolant reaches minimum warm-up, the engine will indeed run.

Initally, that means 130°F for the first stop, then down to 114°F before the engine starts again.

The tolerances change base on battery temp and heater setting. But that gives you the general idea.

 

I'm excited to watch it again. Have another bluetooth OBD on the way. Last one died.

 

I tape off the bottom grill. So far this winter I'm still in the upper 40's to 50.?. Same results last winter.

 

I think it depends a lot on your type of driving. Our daily usage has been dropping the last few months, it's more extended weekend drives, which I think has really helped with mileage. It's short, cold-start trips that really murder mileage in winter. On our latest tank it's been all extended drives. I've got the lower grill 100% blocked, and we almost without fail are using our block heater for first start up of the day. About 100 km into the tank the dash is showing 4.3 (liters per 100 km). Which means actual is probably about 4.6 l/100km, which translates to around 51 miles per US gallon.

I'm sure we won't sustain that, short trips will creep in, but...

 

I'm sorry, I didn't notice you were up north. We live in small town So Indiana and most trips are around town (4 miles from one side to the other) and a few @40 -

 

I'm getting a little over 43 this tank.. Though I filled up before storm last week and was stuck in traffic for almost 2 hours... All roads were blocked.. I'm a little heavy on the throttle and have been using the remote start some mornings

LG-LS980 ?

 

All you regular Prius owners complaining about 5-10mpg loss. My PiP has gone from 100+mpg in warm weather to mid-50's now that the deep cold has set in!

Engine started right up due to single digits last night so my 1.5mile drive to work returned 29mpg.

 

Have not gone back to grill blocking and it's been too cold to work in the garage to install the EBH I bought. My mileage has really tanked since our night temps. have hit the negative numbers and the day time highs are mid 20s. Was keeping it around 50 mpg before the drop and now I'm seeing low 40s.