Details for Car talk Editorial Saturday

Old cars learn new tricks when leaded gas was phased Out

BY RAY MAGLIOZZI
Dear Car Talk:
I bought a 1969 Chevrolet
Chevelle SS 396 recently and
want to know if unleaded gas
will harm my engine. Also, will
using regular unleaded instead
of highoctane unleaded hurt?
I’d rather use the less-expensive
regular, but not sure what to do
here. — Jim
You have no choice, Jim. You have
to use unleaded gas. Will it harm
your engine? Mostly no. When

lead — a known carcinogen — was
finally phased out of gasoline in
the 1970s, older cars like yours
did fine, except for one thing. It
turns out the lead in the gasoline
provided a cushion between the
valves and the valve seats. And
without lead, the valve seats
suffered from something called
“valve seat recession.” Basically,
they got pounded.
When those valve seats got
pounded to the point that they
wore out, they had to be replaced
with hardened valve seats. That’s
the only kind you can get now.
And they’ve stood up well over
time with unleaded gasoline. So
if your Chevelle has already had
its valve seats replaced (which
is pretty likely, unless it’s got
very low mileage), you already

have hardened seats and there’s
nothing to worry about. If your
valve seats haven’t been replaced
yet, when they do wear out, you’ll
replace them with hardened seats,
and then there’ll be nothing to
worry about. Either way, there’s
nothing you can do, so just drive
the car and enjoy it.
In terms of the octane rating,
your only goal is to prevent
pinging. So experiment. First,
make sure the valve timing is set
correctly. Then try the lowest
octane fuel, and when you
accelerate up a hill, see if you
can hear the engine pinging. If
you can, try the next octane level
up from there. Do that until the
pinging goes away.
Pinging, also known as pre-

ignition, is when some of the fuel
combusts in the cylinder when
it’s not supposed to. That’ll
eventually burn holes in your
pistons, which will cost much
more to replace than those valve
seats. So use unleaded fuel with
an octane rating that’s high
enough to prevent the car from
pinging, pick up a pair of striped
bell bottoms, and you’ll be good
to go in the Chevelle, Jim. Enjoy.
***
Got a question about cars? Write to
Ray in care of King Features, 628
Virginia Drive, Orlando, FL 32803,
or email by visiting the Car Talk
website at www.cartalk.com. © 2018
by Ray Magliozzi and Doug Berman
Distributed by King Features
Syndicate, Inc.

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