Eliot Silverman

Eliot Silverman

Thursday, October 28, 2010

Pre Winter Inspection

All summer and fall you get in your car, turn the key and it starts, gets you to your destination without any problems.  So why have it inspected?  Good question.  A good pre-winter inspection looks at over 7 areas that can cause cold weather, winter related problems.  The first I’m going to write about is your battery.

 For your car to start you need a battery with sufficient power to ‘crank’ your engine.  Just because your headlights, radio, wiper blades work does not mean you have a good battery.  These components take very little power to work (less than 10 amps).  Your battery needs to give your starter 250 amps or more for it to crank. Therefore, just because your headlights work, and your radio work does NOT mean you have a good battery.

Auto batteries use lead and acid.  Thru some magic of chemistry the lead and acid produce electricity to start your car and keep it running.  Once it is running the alternator recharges your battery.  The production of electricity is dependent on the outside temperature.  At approximately 70 degrees the battery has 100% of its available power.  At 32 degrees the battery only has 25% of its full power.

To make matters worse, the colder an engine gets, the harder it is to crank.  At 32 degrees, your engine is four times harder to start than a warm engine. 

As you can tell, all summer and fall a weak battery can crank your engine, and lead you to believe you have a good battery.  Once the temperature drops, this bad battery can no longer crank your engine.  If you notice that you car seems harder to crank, you may need a battery.

Batteries are easy to test.  We connect our battery tester to your battery and drain your battery at a rate of 250 amps.  After 15 seconds a good battery will indicate over 10 volts.  A weak battery will indicate over 9.6 volts.  Any reading under 9.6 volts is a bad battey and it must be replaced. 

Next week I'll discuss your alternator and how it is related to your battery.

Safe motoring
Eliot Silverman  B.S. Mechanical Engineering University of Michigan 1979
Owner of Eliot's Complete Auto Repair Shop
3658 N. Lincoln Ave.
Chicago, IL. 60613


  1. Would you recommend finding a garage to do a full service before the Winter or can a DIY inspection be just as good? This is my first Winter with my car and I want to make sure I'm doing everything just right.

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