1: Engine flushes ($100-$200)

An engine flush uses a big, expensive machine and proprietary chemicals to purge your engine of sludge. An engine that's running too hot or one that's neglected can sludge up, and if so, a flush is indicated. A quick peek into the oil-filler cap should let you see any deposits. It's not a normal maintenance item.

2: Fuel-injection cleaning ($125-$200)

This is a fair price for this service, which uses another impressive machine -- but only if your fuel injectors are actually dirty, and you have driveability issues because of it. If your Check Engine light isn't on, and your car's running fine, pass.

3: Oil additives ($5 and up)

There are all kinds of tiger milk on the market, from stuff that's supposed to cut friction and increase fuel economy, to products that promise you can run your engine dry of oil without damage to the bearings. Right. Trust me, if it was that good, it would already be in the motor oil from the petroleum company and in your crankcase when you bought your car new.

4: Gas savers ($10-$400)

We've tested a bunch of gadgets -- from magnets to vortex generators to water injectors and (I kid you not) ectoplasm traps -- that claim to improve fuel economy for various pseudo-scientific reasons. None have helped, and some have actually hurt performance. Your shop may be unscrupulous, or just misguided -- but you've been warned. Any device that purports to increase mileage won't. The EPA has tested more than a hundred, and their results mirror ours.

5: Long-life antifreeze ($4-$8 per quart)

Okay, some GM cars come factory-filled with five-year coolant, and we suggest that owners of these cars stay with it. Your car may not have been designed around GM Dex-Cool's additive package. Almost every manufacturer specifies some proprietary additive package nowadays, and cooling systems can develop corrosion problems if they don't get it. Pouring the wrong coolant into a car engineered for a specific type is asking for trouble. Mixing two kinds without a complete flush in between practically guarantees it.

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