But were too embarrassed to ask!

Interesting. I have often asked Toyota Service managers and tech when to
replace the Timing belt on verious cars: "The belts been on the car for 5
years!" Ans: "Replace it at XX,XXX miles!" I always wondered why Mileage
and not elapsed time. Well: (take a look at the LAST line...)

For preventative maintenance, and to comply with the recommended replacement
interval specified by the vehicle manufacturer. Rubber timing belts
contain reinforcing cords of fiberglass or Kevlar. These cords keep the
belt from stretching or breaking, which is no simple task considering the
strain that is on the belt. Many other engines use a steel chain for this
same purpose.

As the belt accumulates miles, the constant bending every time it passes
around a pulley plus constant exposure to heat causes the rubber to harden
and become brittle. Little cracks start to appear in the rubber. These
cracks are not serious as long as they’re not too deep or cause chunks
of rubber to break loose. The constant stress, heat and bending also
weakens the fibers that make up the reinforcing cords. Eventually the
point is reached where something gives and the belt fails.

Until recently, the incidence of failure peaked sharply after about 60,000 miles,
so the vehicle manufacturers mostly recommended replacing the best at
60,000 mile intervals. On newer engines, this interval has been extended
to as much as 100,000 miles thanks to improved belt materials.

So what happens if you don’t replace the belt? Maybe nothing. Some belts just
keep going and going and will last the life of the engine. Others may fail
at 60,001 miles or even sooner. Since no one can predict the exact mileage
at which a timing belt will fail, the safest bet is to follow the vehicle
manufacturer’s recommendations.

WARNING: A timing belt failure can cause extensive engine damage on many
overhead cam engines. If the engine lacks sufficient valve-to-piston
clearance, a belt failure can allow the valves to hit the pistons
destroying both. The cost of replacing the belt at the recommended
interval, therefore, is cheap insurance compared to the cost of replacing
or rebuilding the engine.

Engines with timing belts that are at risk for this type of damage include:
# All Accura four cylinder, five cylinder and V6 engines
# Audi 1.6L and 2.0L diesel engines
# Buick Skyhawk 1.8L and 2.0L engines
# Chevrolet Geo Metro 1.0L three cylinder engines
# Chevrolet Geo Spectrum and Prizm 1.5L and 1.6L engines
# Chevy Luv pickup truck 2.2L diesel engines
# Dodge and Plymouth Colt 1.5L and 1.6L engines
# Eagle Summit and Vista 1.5L and 1.6L engines
# Eagle Talon 2.0L engines
# 1981-85 Ford Escort (and Mercury Lynx) 1.6L engines
# 1985 Ford Tempo and Ranger pickup 2.0L diesel engines
# Ford Probe 2.0L engines
# All Honda four cylinder engines
# All Hyundai four cylinder engines
# Infinity 3.0L V6 engines
# All Isuzu four cylinder engines
# Mazda 2.2L four cylinder and 3.0L V6 engines
# Mitsubishi 1.5L, 1.6L and 2.0L engines
# All Nissan engines
# All Porsche engines
# Suzuki 1.3L engines
# Toyota Tercel 1.5L engines
# Toyota pickup 2.2L and 2.4L diesel engines
# Volkswagen 1.5L and 1.6L diesel engines
# All Volvo four cylinder engines
# All Yugo engines (if any are still running).