MPG & stopping at stop lights
 

My husband wondered about how the effects of sitting at stop lights in electric mode calculated in the MPG. I mean, if we were in a gas-powered car gas would be consumed while you sit at stop lights and thus be captured in the calculation of miles per gallon of gas, but how is that same stopped time while in electric mode, when no gas is consumed, captured in miles per gallon of gas?

Thanks!

Sadie

Re: MPG & stopping at stop lights
 

You're not using any gas, nor are you moving, so it won't factor in at all... MPG = miles per gallon... 0 miles being traveled / 0 gallons being used.

Just reset your average MPG and watch it while at a stop... no change.

Re: MPG & stopping at stop lights
 

Well, technically you're still using energy that has to be replenished by the engine. I still haven't found out precisely how Ford's hybrid system works, but assuming it's like Toyota's... when the battery runs too low, your engine will be forced to run and consume gas even while stopped.

Re: MPG & stopping at stop lights
 

As far as I know you're correct Jason, makes perfect sense.

Re: MPG & stopping at stop lights
 

but don't the brakes replenish the battery? I would agree that in the absense of energy from the brakes that the engine would be the source but aren't the brakes the source of the energy?

Re: MPG & stopping at stop lights
 

Not all the energy supplied by the battery to move the car can be returned by the brakes or any other passive method. There are losses due to heat, friction, tire rolling resistance, the stereo, the brake lights, headlights, the drag of your weight, wind drag, a not-one-hundred percent-efficient means to use and regenerate energy and other stuff. As a result, the engine does need to kick in once in a while, even while sitting at a light. Otherwise, you have the world's only perpetual motion machine:-) I think Ford would sell a lot of them if it had that technology.

Re: MPG & stopping at stop lights
 

I have been stuck in traffic or going very slowly in EV when all of the sudden the ICE will turn on. It is true, as Jason says, you can be stopped and suddenly start to use gas if the electrical system needs to be replenished.

Re: MPG & stopping at stop lights
 

Only when you're slowing down. Once you're stopped (actually once you get below about 5 MPH) the brakes can't recover any kinetic energy. There is a power drain from the various electrical systems, lighting, radio etc. that will eventually bring the HV battery low enough to require the engine to start. Depending on charge state it could take several minutes.