5 car maintenance scams

This post comes from Jim Wang at partner blog Bargaineering.

Finding a good mechanic or shop you can trust is difficult, so when you find one, it pays to stick with them. That's why I take my car to the same place every time I have an issue.

There have been a couple times when I, or my lovely wife, have taken the car in for a minor issue and they sent us on our way without a bill. Once, one of us rolled over tar that stuck to the tire, leading to a shake and some thumping. We took it in and they scraped it off, free of charge -- they didn't even charge for labor. That's good service and, when you think about it, how business should be done.

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That's what makes some car maintenance scams so egregious. It's businesses thinking of the short term, rather than the long term, and wanting to make a quick buck.

Many of these are scams because they don't rip you off outright; they just overcharge you for a service you don't need: Post continues after video.

Engine shampoo. My friend took his car to the shop for some routine maintenance and the salesperson sold him a service to shampoo his engine. They cleaned off the oil, dirt, grease and grime that the exterior of every engine in the world has (it's making hundreds of little explosions, so of course it will get dirty!) for $100 or $200. The service is completely unnecessary. If you really want to clean your engine, you can buy your own shampoo for much less.

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Engine flush. While shampoo is for the outside, an engine flush is for the guts of the engine. In some cases, a flush is necessary if your engine has a buildup of sludge or other gunk. But many places recommend a flush even when it's unnecessary because they know most people will agree to it.

The only time you will need an engine flush is if you've been driving the car for years and notice a buildup of material under the oil cap. If there is sludge, it will get cycled into the motor oil and some of it will collect on the oil cap. If the shop says you need it because your oil is dirty (it gets dirty and loses that nice brown color the moment it cycles through the engine), run.

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Fuel injector cleaning. This is another classic that preys on the ignorance of drivers. Fuel injectors do need to be cleaned, but usually not until they've put on a lot of miles (more than 100,000). So if your car has 20,000 miles and the mechanic says you need them cleaned, he's likely trying to sell a service you don't need. If you are really concerned, you could add fuel injector cleaner to your gas tank on your next fill-up. (It has been recommended that you use it every other oil change -- that's how infrequently).

Gas-saving devices. They do not work. Consumer Reports has studied this extensively and has yet to find one that actually improves fuel economy. Don't accelerate too quickly, don't slam on the brakes, empty your trunk of junk, learn to coast effectively, pick up some tips of hypermilers, and don't buy "gas-saving devices."

Transmission flush. If you have an automatic transmission, the mechanic might recommend that you flush it and replace the fluid. I know, from when my dad flushed and replaced the transmission fluid in his car, that this is not something you want to do yourself as it can take a lot of time and can get messy. But it's something you won't need until at least 60,000 miles and not even then, if you have a filter -- many cars do. Check your owner's manual for how often this should be done.

Those are some of the worst car maintenance scams out there, but they are certainly not the only ones. Whenever a mechanic recommends you do something, take it with a grain of salt unless you have the level of trust I have with my mechanic. Even then, double-check their recommendations against your manual, online resources, and any car experts you know before you shell out a few hundred bucks for a procedure.

What's the worst thing a car mechanic tried to pull on you recently? An engine shampoo? Washing your undercarriage?

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