Why mileage gets worse in winter

because the gas motor runs longer to get the car and cabin up to temp = less mpg

 

Your body weight and each passenger's weight combined puts a strain on your mileage.
When I read about great mileage, I'm picturing it's from a solo 150 pound guy or 120 pound gal.

 

Yes...but in the hierarchy of hypermiling reducing one's personal weight is pretty far down the list.

 

For your education & entertainment... some real-world winter data:

 

I hea/rd things like, an additional 100lbs load will see a loss of fe of 2% MPGs. DRLs always on also will account loss of 2% MPG fe due to the energy need to stay lit up.

 

Quick question. What were you using to get coolant temp and rpm to display?

 

Torque Pro with Recorder on my phone via Bluetooth from the ODB-II port.

 

Ok....but if you are 100 lbs overweight you should probably be focused on losing that for your health and not to save a few pennies on gas.

 

For the most part:
1. Engine wont shut off to pulse n glide nearly as much because its trying to keep target temp. So your engine is going to be on at stop lights and coast for no reason a ton more instead of instantly turning off after a minute like warm weather.
2. Air is much thicker and is harder to push through. ~13% thicker going from 80F to 20F.
3. The cold battery restricts the current flow so it wont go into EV mode with as much power as normal.
4. Winter gas has 32.97 kWh of energy vs summer gas with 33.557kWh of content (98.25%).
5. Using the heater really exacerbates the cold blooded idling engine problem.
6. Wet weather and dirty roads up the rolling resistance of the road by up to 30%.
7. Increased slow moving traffic in bad weather.
8. The majority of energy is used to overcome drag due to air resistance and rolling resistance,and keep the engine warm... weight is next but much smaller.

 

+rolling resistance higher on colder tires
+Lubes thicker

 

Please note me i have 3 Gen prius in winter average MPG how much you have?? I have 43 and think something wrong in my car.

 

That sounds more like full headlights (and all the accessory lights that come on with them) in stop-and-go city traffic.

Headlights at highway speed should be under 1%. Traditional incandescent DRLs should be significantly less. Prius LED DRLs should be far less.

 

I'm going to have to read this whole thing. I'm getting only 30mpg average after 3 tanks in my Avalon Hybrid after getting 42 average during the summer up until the middle of November. I got the grill blocked off about 95% without overheating problems, and it's not even officially winter yet!

 

I would monitor engine temps with that amount of grill block, that's a long way from the design grill opening. Do you know where the inverter radiator is, ie: top, bottom? I would for sure not block that. If your radiator fans are coming on a lot, you've definitely overdone it. I'd also be very cautious, maybe take it all out, if you've got any long uphill climbs.

 

I forgot to mention I also have an engine block heater.

As for blocking, I noticed the inverter part in the top of the radiator. So I only blocked that 50%. I left the cardboard on the radiator in two pieces so that I could slide one over if I needed to. Only a small part of the engine radiator is barely showing. The rest is covered by the cardboard.

I have a ScanGauge 2 that shows engine coolant temperatures. So far the hottest I have seen is 186°F. That was climbing a mountain pass from about 5,500 ft to about 7,500.

 

I.e. not even getting fully warmed, which would be 195F.

 

Do you think the thermostat could be bad? (Do these even have thermostats?)

 

Thermostats can fail gradually. The one instance I've had where I thought something was definitely wrong (with a Honda Accord in the 90's): I was driving into work against the flow of traffic, early Saturdays, and cool late-fall conditions. Pretty much had the road to myself.

Coming off the freeway, I'd notice the engine temp needle (remember the good old days when cars had those...) was right down at the bottom.

It turned out the two things were going on the thermostat. First it's internal mechanism was opening the gasket too soon, closing it too late. And secondly, the rubber of the gasket was getting brittle, the edge feathering. Both factors meant the thermostat was letting coolant into the radiator too soon, too much.

I suspended the old and replacement thermostats side-by-side in a pot of water and brought it up to near-boil, watched the difference in performance, to satisfy myself I was improving things.

I would think it would take 100K miles before a suspect thermostat would be worth replacing, just as a wear item, just guessing.

 

Yes. And there's a chance that the previous owner put a lower temp thermostat in there since he did live in the Dallas / Fort Worth area and may have thought his hot weather merited a cooler thermostat (although I have my doubts about that because I supposedly have all the service records and can't find anything about the thermostat. But that doesn't mean he didn't do it and didn't keep the receipt.)

I guess I'll get another thermostat. I usually get Toyota products, but do you think with my colder weather it would be better with a slightly warmer thermsotat, say 200°F? It's been dipping down to -10°F already!

The Avalon has a temp gauge! Oddly it's not linear. The needle starts moving at about 90°F. It hits middle at about 140° and stays there up to 186°F. I don't know what it does after that. But it's obviously rigged to stay exactly in the middle between an acceptable temperature range.

 

Avalon sounds like a good vehicle. I like the looks, see them here occasionally.

I really don't know about thermostat temp ranges, tend to bat out of league sometimes. Hopefully someone else will comment.

I do know in (mild) winters here, when I had scangauge connected, I'd often see coolant plateau around 170F. It would only hit 190~195F climbing Mt Seymour. And that's one time I removed all grill block, didn't want to risk it.