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Under the Hood: Stop corrosion on battery post

| Friday, July 4, 2014, 8:57 p.m.

Question: Could you explain why my 2011 Lincoln MKZ battery post develops green corrosion on the positive post? The mechanic at the dealership and the service manager said that some batteries do that and it is normal. The manager said the vents on the wet batteries cause the post to gather this acid and corrode. He suggested a couple of deterrents, such as a copper penny between the posts, spray-painting the post or putting grease on the post to shield it from corrosion. Do you have a solution or idea?

Answer: I believe your battery has a poorly functioning seal between the battery post and case that is allowing vapors or acid to sneak up into the terminal connection. This is more of a nuisance than a problem. I've had fairly good luck using the red and green felt terminal protectors, placing them beneath a just-cleaned terminal. Coating the post and terminal with some “Brush-on NCP-2 Battery Corrosion Preventative” is another method that can bring relief.

If your battery terminals have crud growing atop them, there's a good chance corrosion is working into the more critical, less visible clamp/post connection. Corroded or loose battery terminals can cause difficult or no-starting, charging system issues, and some really weird symptoms to occur with on-board electronics. The good news is vehicle damage is unlikely. It's the symptoms that can be unpleasant.

Cleaning terminals is a fairly easy process. A check of the owner's manual for precautions involving battery disconnection/replacement is a good first step. Yours indicates the transmission will need to undergo a learning period after reconnection to restore shift strategies and may shift a bit firmly or softly until things sweeten. An inexpensive battery “memory saver” can be plugged into the lighter socket.

Eye protection is a must. The black negative terminal should be removed first and installed last, and don't allow the terminals to touch each other or any other parts! Never disconnect a battery cable with the engine running or key on.

Avoid twisting the terminals excessively. Loosen the nut further and gently spread the clamp apart with a large screwdriver. Mix up a container with 2 cups of water and 2 to 3 tablespoons of baking soda. Immerse the removed cable clamps for a minute or so, one at a time, and pour a small amount of fluid/paste over the vacated battery posts. Clean and pat all parts dry with a dampened rag, then use the terminal cleaning brush to bring up some shiny connecting surfaces. Finish up with your preventive products and securely snug the clamps. Wash your hands right away!

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif.

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