Staying on track with belt changes

Question: I have a 1997 Toyota Avalon with only 27,000 miles on it. I took it to a dealer recently for the six-month oil change, and he said I should have the timing belt replaced. He said the belt should be changed every four years, as they wear out. I had it changed on his advice but was wondering if what he said was true or meant to drum up business?

-- A.B.

Answer: Though what the dealer told you is not the policy recommended by Toyota Motor Corp., it was generally good advice about the importance of timing belts. Still, almost nobody recommends changing them that often.

Timing belts transfer power from the engine crankshaft to the overhead camshaft, which opens and closes the cylinder valves. It’s important that a belt not slip, because that would throw off the valve timing.

If a timing belt slips or breaks, that can allow a valve to open at the wrong time or stick in the open position. When that happens on certain engines, including the 3.0-liter V-6 in your Avalon, the piston can hit the valve at the top of the engine stroke. The impact can damage or even destroy the piston, requiring a major engine overhaul.

Toyota recommends replacing the timing belt on your Avalon every 60,000 miles without respect to how many months the belt has been in use, according to guidance provided by automotive publisher Alldata.

For models produced from 1999 onward, Toyota advises replacing the belts every 90,000 miles or 72 months. Toyota has never had a recommendation to change belts on the 48-month cycle your dealer suggested.

By the way, it is possible to inspect a timing belt to determine whether it should be replaced before the recommended time. The procedure includes looking for general wear, cracked teeth, nicks on the pulleys and improper pulley alignment.

But your mechanic may charge nearly as much labor to do such an inspection as to replace the belt outright.

With your Avalon, the belt itself costs $43.85 and the recommended labor is 2.7 hours, according to the Alldata rate book. At typical labor rates of $60 to $100 an hour, you might as well have a new belt put on if you face paying for even one hour of labor.

In general, I think timing belts are poorly designed, though they are cheap to produce. Few consumers will consider a timing belt design in deciding whether to buy a car, so manufacturers don’t encounter much resistance in using them.

Many engines use timing chains that do not need replacement and seldom break. A few models even have gear-driven camshafts with pushrods, a design generally considered an anachronism but remarkably reliable.

Q: Why haven’t automakers come up with a way to gauge whether a battery is about to go dead? Is there any way to have a warning light in the car?

It doesn’t seem right that something as small as a battery can leave you stranded. Why don’t owner manuals at least give you a time frame for when a battery needs replacement? The manual of my 1997 Chevy Malibu is silent on the issue.

-- D.E.

A: Batteries die for many reasons -- such as overheating, sediment in the cells, freezing and sulfation -- and building in sensors to measure all of them would be impractical.

Many batteries contain a view cell with a built-in hydrometer that changes color from green to red or black when the battery is on its last legs. But that only checks one of the six cells in a 12-volt battery.

A mechanic can perform several tests, such as measuring whether the battery has a fully charged voltage of 12.66 volts and putting a load on the battery to see how quickly the voltage bounces back afterward.

You can sometimes get a sense of when a battery is going out by how well it cranks the engine on startup, though that’s far from reliable.

The biggest cause of failure is sedimentation at the bottom of a cell that creates an electrical bridge between two plates, shorting out a cell, according to Interstate Batteries.

As a general rule, batteries last about three years, though some may function twice as long as that.

A sure way to damage a battery is to allow it to go dead, as when you leave your lights on, or let it sit uncharged for a long period. If that happens, it is best to have it put on a battery recharger rather than allow the car’s charging to restore it.

Batteries are not very expensive, and you can take the safe route by just replacing it every three years.

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Ralph Vartabedian cannot answer mail personally but responds in this column to automotive questions of general interest. Please do not telephone. Write to Your Wheels, Business Section, Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012. E-mail: ralph.vartabedian@latimes .com.