How to calculate the cost savings of a hybrid

Dear Car Talk:

At one time, hybrid cars clearly made sense. But with seriously improved gas mileage for all cars, is that still true? What formula can we use to decide if the extra cost of a hybrid is worth the improved gas mileage? – George

RAY: It's a good question, George. Now that there are so many hybrids available, it's worth doing the math. And here's how you'd do it:

First, you figure out the difference between the hybrid and nonhybrid version of the same car, equipped the same way.

Let’s use the Toyota RAV4 as an example. A 2020 LE AWD starts at $25,950. A hybrid version of the same exact car starts at $28,350. That’s a difference of $2,400. Now the question is, how long will it take you to save $2,400 in gasoline?

To do that, you’ll need to know the annual fuel cost for each car. Start by going to and looking up the average miles per gallon of each vehicle. For the RAV4, it’s 30 mpg. For the RAV4 Hybrid, it’s 40 mpg.

Then you take the number of miles you drive in an average year (let’s say it’s 20,000 miles) and divide it by each of those mpg numbers. That tells you how many gallons of fuel you’d need to buy in a year.

For the RAV4 (20,000 miles/30 mpg) it’s 666.67 gallons a year. For the RAV4 Hybrid (20,000/40), it’s 500 gallons a year. Then you multiply the number of gallons you’d buy in a year by the price of a gallon. That varies, obviously, but let’s say it’s $3 a gallon.

So, to run your regular RAV4 for a year, it’d cost you $2,000 in gasoline (666.67 gallons x $3 per gallon). Where the RAV4 Hybrid (500 x 3) would cost you $1,500 a year in gasoline.

Now you can put it all together. You know that you would save $500 a year in gasoline costs with the RAV4 Hybrid. So divide the extra cost of buying the hybrid ($2,400) by the amount it would save you per year ($500), and you learn that it would take about five years for you to “pay off” that premium you spent on the hybrid, before you started banking money.

So if you keep your cars for six, seven or 10 years, it’s clearly worth it. If you keep your car for three or four years, it’s probably not.

Now, there are other variables. For instance, hybrids use regenerative braking, so you’ll spend less on brake pads and rotors with a hybrid. You’ll also be using the gasoline engine less, so your cost of maintenance (oils, fluids, belts, filters) will be spread out over a longer period of time.

The price of gasoline is also a big variable. If the price of gasoline drops to $2 a gallon, it’ll take you seven years to earn back that hybrid premium. If gasoline goes up to $4 a gallon, it only takes three and a half years to pay it off.

And some people believe there’s value in decreasing pollution, increasing American energy independence or simply not having to go to a gas station as often. We don’t have the formulas for that stuff, George.

But you can at least get a rough idea of the basic economics with the above calculations.

What is ‘lugging the engine’?

Dear Car Talk:

I drive a stick shift, and I can tell when I am "lugging the engine." But I don't know what that actually means. What exactly is going on in the engine that causes that "lugging" feeling? And is it doing any damage to the engine? Thanks! – Judy

RAY: Lugging is pretty much what is sounds like, Judy. If you're lugging an 80-pound prize-winning rutabaga up your stairs, that implies you're dragging it, and struggling to get it done.

Similarly, lugging the engine refers to trying to accelerate when you’re in too high a gear. So put most simply, you’re straining the engine. You’re making it struggle.

Imagine if you were on your 10-speed bike, and you got to a steep hill and tried to climb it in 10th gear. You’d be struggling and straining, too, and you might even “stall.” That’s because, like your car’s engine, you’re not using the mechanic advantage that the lower gears are designed to afford you.

And when the engine is struggling – when it’s trying to move the car but can’t get up to an engine speed where it can turn easily – it will begin to overheat.

It’s not the kind of catastrophic overheating, like when you see steam coming out from under the hood. But when you lug the engine, you’re making the cylinders and pistons run hotter than they normally would. And over time, that damages the engine.

Will it damage the engine if you lug the engine once in a while for a few seconds, and then shift to a lower gear and correct it? No. But if you get in the habit of shifting too soon, and lugging the engine after each shift, the excess heat will shorten your engine’s life.

So you know what to do, Judy. And now you even know why.

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