Perform gauge and listening tests
Leave the hood open. Make sure the emergency brake is on and the car is in Park (or neutral in manual transmissions).
- Turn the key to the On position. Look for the oil pressure, brake pressure and alternator (battery) lights on the dashboard. If the car has gauges for these systems, they maynot light up. (But if there are no gauges and these light up before you start the car, that's good. If they don't, they are either burnt out or disconnected.) Start the car and see if the lights go off. If not, ask the owner what the problem is.
- Does it start right away? If so, check the tachometer. This is a gauge that indicates how fast the engine is running, measured by the number of revolutions-per-minute, or rpm. Look for a gauge with these letters. Most cars will rest steady a little below 1000 rpm when warm. Depress the accelorator pedal a few times and watch the tachometer rise, holding it at about 3000 rpm for a few seconds. Listen to the louder, higher-pitched sound of high rpm. Then let off the accelorator pedal. Does the engine stay at that high level for a bit, then settle back at a comfortable range once you've released the pedal? Or does it maintain a high, loud sound? If it stays at the high, loud level, the idle needs to be adjusted. Fortunately this is not too expensive.
- Although a consistent ticking while idling is usually normal, a loud chatter or refusal to hold at a certain rpm level are sometimes the harbinger of hefty mechanic bills. On the other hand, the infamous knocking and pinging sounds may only require a tune-up or change of gasoline: high-octane gasoline will often silence the knocks and pings.
- Watch the tailpipe while depressing the
accelerator, looking for the color of the exhaust. White is OK when the engine is cold, but could indicate a serious problem if it's already warm. Blue means engine work is likely needed, and black means a minor adjustment. Once the tailpipe is cool (be careful), wipe the inner surface of the tailpipe with a rag or your finger: white or gray dust is normal. Thick, greasy soot means the car burns a lot of oil--this can be serious.