COLUMBIA, Mo. -

They've been on cars and trucks for years, maybe you didn't even know it was there. It's called a skid plate, and it protects your car's engine.

Is it costing you money? ABC 17 News looked into how some drive-through oil change shops are increasing their bottom line on your dime.

Many of us do not know how intensive removing a skid plate is, or isn't.

But is it worth an extra $15 tacked onto an oil change? At least one shop said it is.

We took the same car to the Joe Machens dealership and had them demonstrate how long it takes to remove a skid plate.

It was gone in less than 60 seconds...more like 18 seconds.

That's how long it took a Joe Machens mechanic to remove the skid plate from a Mazda SUV.

Some shops are charging $15 dollars to remove that same skid plate, almost a dollar per second.

"To service the car and change the oil we do not charge for this."

That mechanic said it part of changing the oil.

Most drivers would agree, until you go in for a $30 oil change and see an extra charge on your bill hiking it up to $45.

YOu should be able to get out of paying the up-charge if they added the charge without telling you first, but why are some places charging $15 dollars for this, and others consider it part of the service?

"I couldn't tell you. It's a very simple piece of the vehicle to remove," said the mechanic.

He said it's no different than removing the engine cover off the top to get to the oil filter, it's just plastic.

"We don't charge for it but I understand some are charging $15 to remove this piece of material."

He also said your car is a big investment, and some drive-through shops and big box stores don't have trained professionals doing the work.

Like any business, he said they're in it to make money, and the business is competitive with small profit margins.

"It could be that their bottom-line isn't where it needs to be. We don't make money on our oil changes. But it's a service we provide for our customers."

Most drive-through oil change businesses are independently owned, and not all owners choose to pass along this up-charge.

ABC 17 News was told there's plenty of competition in the oil change business, so if you are asked to pay one of these fees, the best thing to do is go somewhere else.

It's also important to know your car. Most cars just have a few screws but some trucks built for off-road could have several.