Husband's mind is operating in the wrong gear

February 13, 2009

Dear Tom and Ray: We recently bought a 2008 Prius and just love it, love it, love it. But we're having a bit of a discussion about how to use the "B" on the gearshift. I say it's like a downshift, and you should use it only temporarily, while going down a steep hill or coming to a stop. You use it to save the brakes, then return to "D." My husband thinks it's fine to drive most of the time in the "B" mode, since it regenerates electricity and recharges the battery. Who's correct? And if "B" is the gear to use all the time, why didn't Toyota just call it "D" and forget the separate braking option? Thanks for your help! - Gayle

TOM: Gayle, you're 100 percent right, and your husband, unfortunately, has his head up his brake line.

RAY: When you shift into the "B" mode, you increase the drag created by the regenerative portion of the brakes. And while that extra friction does produce some electricity to help recharge the battery, the "B" mode's primary purpose is to simulate downshifting, or engine braking, when you're going down a long, steep hill.


TOM: The "B" mode's secondary purpose is to give guys something to fiddle with while they're driving. And after THAT comes creating more electricity to recharge the battery.

RAY: In any car, hybrid or not, when you go down a long, steep hill, you run the risk of overusing your brakes. That makes the brakes overheat, which leads to brake fade (when the brakes become less effective). Even worse, if the brakes overheat badly enough, the brake fluid can boil and cause the brakes to fail completely. So it's always recommended that you downshift in those circumstances, rather than ride the brakes, to keep the car at a safe, reasonable speed.

TOM: But since the Prius has an unusual propulsion system and transmission, they've essentially "faked" a downshift mode for just that purpose.

RAY: So unless you're driving under conditions where you specifically need the equivalent of engine braking, just leave it in "D," Gayle. But try not to rub it in too much. Remember, husbands have extremely fragile egos.

Dear Tom and Ray: Help! I have an '04 Chevy Trailblazer, and I live in the far north of Canada. It's minus 24 degrees as I write this. Can you tell me what the benefit is, to my engine, of using a block heater? - Emily

TOM: Well, the primary benefit is that your car will start, Emily.

RAY: For those of you lucky enough not to live in the great frozen north, a block heater is an electric heating element that's installed in your engine block. You plug it in overnight with an extension cord, and it keeps the engine block, and the coolant inside of it, warm. And that, in turn, keeps the oil from thickening up.

TOM: When an engine gets bitterly cold, the oil gets thick, like molasses. If the moving parts of your engine have to push through this thick oil just to get started in the morning, they may not be able to do it. So the block heater keeps the coolant warm, and that, in turn, keeps the oil just warm enough so that it moves easily.

RAY: That has benefits for your engine as well. Most significantly, since the oil moves more easily, it circulates faster and gets to moving parts of the engine faster. So there's less time just after the engine starts when key metal parts are unprotected - or underprotected - by oil. That means your engine lasts longer.

TOM: The prewarmed coolant and oil also allow your engine to warm up faster and reach operating temperature sooner. That means you get less oil dilution from cold, unvaporized gasoline, and better fuel efficiency.

RAY: AND it means you get heat to your feet faster. When it's minus 24 degrees, don't tell me that the benefit of a warm passenger compartment isn't as important as any benefits to your engine, Emily!

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