UNDER THE HOOD Manufacturers shifting from belts to chains

Q:When car shopping, do you think it is important to consider if a vehicle has a timing belt or timing chain? After seeing friends pay hefty charges for timing belt replacements, I wonder why timing chains are not more widely used.

—Scott M.

A: There is a shift occurring where some manufacturers are going to chain drive for the camshaft/crankshaft connection in addition to those that already run them. Timing belts are lighter, quieter and supposedly less costly to build, but they burden the vehicle owner with replacement cost, typically at 60,000 to 100,000 miles. Timing belt failure can also be an expensive catastrophe on interference engines if valves and pistons collide. A timing belt replacement job typically includes renewing belt tensioners and the water pump, if driven by the belt. Cost can range as high as $1,000. A timing chain may eventually require replacement as well, at similar or higher cost, although many are claimed to last the life of the engine. Excessive noise is the tip-off a chain system is worn and heading toward failure.

I'd certainly take a look at this when choosing a potential vehicle, new or used, but there are many other factors to consider as well.

Q: My battery light has been coming on for short periods of time and then turning back off again in the most unpredictable manner. Sometimes it will go for weeks without happening. I've taken it in twice and nobody knows what to do. How worried should I be about this?

—April B.

A: An illuminated (battery symbol) light indicates a fault in the vehicle's charging system. If the alternator (charging device) is not producing adequate electricity to operate all the systems at hand, the battery will soon discharge. This could lead to a breakdown or failure to restart after parking. It doesn't sound like you've noticed any low-battery symptoms, so the illuminated light may be somewhat of a false alarm, or the fault occurs only briefly.

A careful inspection/testing of battery terminal connections and alternator connections is a good place to start. Unless something turns up, an accurate diagnosis will unfortunately need to be made during one of the episodes. An inexpensive voltmeter placed across the two battery terminals during an episode could bring some piece of mind or expedite a roll-the-dice repair attempt. Normal battery terminal voltage/engine running should be 13.5 to 14.5 volts. 12.6 volts or less indicates no charging is occurring.

ABOUT THE WRITER

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at bradbergholdt@gmail. com; he cannot make personal replies.