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Video: What happens if you use the wrong fluids in your car?

Consumer Reports News: October 29, 2010 07:38 AM

It's not uncommon for people to mix up or use the wrong fluids in their cars, and if they do, the results can vary from irritating to deadly. Below, we outline the potential damage you can do to your car, or to yourself.

"Adding antifreeze to the windshield-washer reservoir might just create a slimy mess," said David Champion, senior director of Consumer Reports' Auto Test Center in East Haddam, Connecticut. "But a British health study found that filling the reservoir with only water creates a good breeding ground for the bacterium that causes Legionnaires' disease. Consumers should check their owner's manual before they top off any fluids under the hood of their car," Champion said. People should check with a mechanic, or even the folks behind the counter at the local auto parts store, if they have any doubts.

The video highlights the proper way to check and refill your car's fluids, demonstrating where the resevoirs are located.

Here's what could happen if you use the wrong fluids:

Motor oil slip-ups. The brand of motor oil matters little, but its viscosity grade (10W-30, for example) is important. Use only what the owner's manual specifies. Using the wrong oil can lead to reduced lubrication and shorter engine life. If the manual says to use synthetic oil, do so. Contrary to what some believe, adding synthetic oil to regular oil won't harm the engine, but there's also no benefit in doing so.

Battery fluid. Some car batteries have accessible individual cells that might need replenishing with a little water to cover the lead plates. Only use distilled water, which contains no salts or minerals. If tap water is added to a battery's electrolyte liquid, it can allow minerals from the water to build up on the battery's internal lead plates, which will reduce the battery's power and shorten its life.

Be cool with the water. A car's cooling system uses a blend of water and antifreeze; properly called coolant, at concentrations (typically 50/50) designed to keep it from freezing on a cold day and boiling on a hot one. Adding too much water to the mix can make it more susceptible to freezing and boiling. That can keep the car from starting when it's freezing and cause overheating in warmer weather. Tap water could also lead to mineral buildup in the cooling system, reducing its effectiveness.

Adding diesel fuel to a gasoline-powered car's tank. This will make the engine stumble and knock, if it runs at all. Fortunately, diesel pumps have oversized nozzles, so that mistake is hard to make. Depending on the quantity of gasoline that's added to a diesel vehicle's tank, it could do little harm or it could damage the fuel pump, injectors, and other parts. If the mix-up is caught soon enough, a technician can limit the damage by draining the contaminated fuel. Meanwhile, don't run the engine.

See the complete report from our November 2010 issue, "What if you use the wrong stuff?"

Learn more about car care in our guide to car maintenance.

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