One single kind of loud clunk from the starter each time you turn the ignition switch to "crank" is usually worn contacts in the starter solenoid. They can be replaced, but most people just replace the entire starter. This always starts out being intermittent and will crank the engine eventually if you cycle the ignition switch to "crank" enough times. Sometimes a jump start will help enough current get through the worn contacts and the engine will start, but that won't help for long.
A rapid, repeated click, click, click indicates a run down battery or loose or dirty battery cables. A jump start can overcome either of these problems. To find this, measure battery voltage while the car sits for a long time. A fully charged battery will measure near 12.6 volts. If the voltage slowly drops over time, there is something draining the battery.
If the battery voltage is always down to around 11.0 volts or less, one cell is shorted and the battery must be replaced.
After the engine is running, measure the battery voltage again. It MUST be between 13.75 and 14.75 volts. If it is low, the alternator is not recharging the battery. This often starts out as an intermitent problem so having the alternator tested just means it was working when it was tested. It can fail one minute later.
When there is no sound after sitting for two days, do any other lights or functions work? If the headlights and dome lights are nice and bright, that leaves out a battery problem. If no lights or other functions work, the battery likely has been drained. Look for cell phone chargers, aftermarket radios, trunk light stuck on, or anything else that is staying on. Proof that a drain is causing the problem can be found by disconnecting the black negative battery cable when you park the car, then letting it sit for two days. If it starts just fine after reconnecting the battey cable, something is draining the battery.
Tuesday, March 9th, 2010 AT 11:28 AM