I'm still not exactly clear on why my FE suffers in cold weather. I think it has to do with two reasons

1. Colder / Denser air requires more fuel per same volume of air, hence the use of cold air intakes to up engine power.<
2. Lowered volume of air in my tires due to colder air.<

Unfortunately we've had some cold mornings this week (~40degrees F), and that's half of my commute.

Anyone have similar experiences?

Takes longer for the engine to warm up. Increased warm-up penalty.

What?! I can't believe it's that cold already. I just returned to Savannah for school from south Florida and I'm enjoying highs in the 80s.

Gil,

Your Engine and catalytic have to warm up before the system can optimize MPG. This happens in the frst few minutes of your trip. This causes low MPG at first which is then averaged out on longer trips. If your commute is short, you'll see a large hit to your MPG.

Another factor on very cold days is your use of heat to keep you warm. This cools the Internal combustion Engine (ICE) and limits the systems ability to run electric only which reduces MPG in low speed driving (there's plenty of heat generated at high speeds).

JeffD

Digraph, don't feel too bad because cold weather affects every car/ICE out there not just hybrids. Just think of those poor SUV/Hummer folks that think they're getting 10mpg when in reality its only about 8....

Make and model?


Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Actually I have a 2.0 L gas VW. But I figured the ICE physics was the same.
I'd probably be considered a hypermiler, by pure ICE standards for such a heavy/inefficient car

Hi,

The reason I ask is cold temperature performance is somewhat vehicle dependent. Folks have rediscovered that what works in one hybrid electric won't necessarily work in another. So if I suggest preheating your traction battery, you'd probably answer, "Say what?"

I forgot to ask, manual or automatic?

BTW, have you visited "CleanMPG.com"? They have a lot of gas experts and share our interest in vehicle efficiency across a broader range.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Cold weather has benefits for gas engines. First of all, your engine will provide more power when colder since the cold air flowing into it will be more dense which will result in more fuel being packed in with this dense air to keep the air-fuel mixture properly balanced. This will result in more horse power output.

This effect is like a very mild form of turbo charging as more air can be packed into the engine cylinder when it is cold and dense. Air reduced by 30 degrees is equivalent to 1 PSI of turbo boost. With cold weather you get this effect for free.





Intake Air Temperature

Engine Power Loss

Example Power Output

20C

%0

224 hp

40oC

3.50%

216 hp

60oC

7%

208 hp

80oC

10%

202 hp

100oC

13%

195 hp

Toyota and most automakers take advantage of this effect by placing the engine air intake at the very front edge of the engine compartment under the hood to avoid pulling in hot under-hood air into the engine. The table below describes the relative power loss expected by a gas engine as outside temperatures increase:


The second advantage of cold weather is that the engine can run on lower octane fuel before experiencing engine knock. Thus, when the temperatures are in the 30's for instance, you can notch down to a lower grade of gas without reducing gas mileage and performance. I typically use premium gas in spring through fall and mid-grade in winter (Chicago area)

This forum word processor doesn't seem to handle tables well. See legible table below from my last post:


... Air Temp......Engine Power Loss......Engine Power Output
........20 F............................ 0%............................ 224 HP

........40 F......................... 3.5 %........................... 216 HP

........60 F.............................7%.................. .......... 208 HP

........80 F.......................... 10%.............................202 HP

......100 F.......................... 13 %........................... 195 HP