An Infrared Thermometer available from Sears and other tool retailers for under $100 is very useful for checking temperature of alternators, various engine parts, batteries, turbochargers and other engine room components. Make sure it reads to several hundred degrees. If you do this periodically in the same places and under the same operating conditions, you will get a sense of what is normal. Put a dot on the equipment with a paint pen or other marker and measure with the IR thermometer next to the dot. Keep a log of the temperatures. The IR thermometer quickly reads the temperature without touching the equipment. If, at some point, the temperature begins to creep up without some explanation such as a very hot day, you likely have just identified an incipient problem and you will have identified it long before it is a real problem. This method is used in power plants and manufacturing facilities to identify problems at an early stage.