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Spinning My Tires
is one man's view of the world of cars. Random thoughts, ideas and comments pop up here,
all of them related to owning, driving and restoring cars. I've been doing this car thing
as long as I can remember, and have enjoyed a great many car-related experiences, some of
which I hope to share with you here. And I always have an opinion one way or another.
Enjoy.
E-mails are welcomed--if you have thoughts of
your own to share, please send them.
Additional Spinning My Tires
editorials can be found on the Archives page.
8/1/03
Debunking Some Popular Automotive Myths
I’m sure you’ve all
heard at least one of these before:
There are stories of wonderful (or
horrible) things happening to cars because somebody misused motor oil or put 93-octane
fuel in their tank. One guy told me about a VW Beetle that a friend had restored, which,
upon start-up promptly seized tighter than a 7-day clock. Everyone blamed the problem on
the synthetic oil he was using as break-in oil. Then there are the folks at gas stations
who put the expensive gas in their low-compression 4-cylinder engines, thinking it’ll
help them pass an emissions test or make more power or “clean the gunk out.” And
in the old car hobby, who hasn’t heard about the “leaded gas crisis?”
Whatever will we do without the precious lead lubricating our valve seats and boosting our
octane ratings?
Well, I’ll tell you. This is
the straight dope, coming from a guy who built and raced some pretty fast cars, who worked
with engineers from major manufacturers and has years of hands-on experience. So take all
this to heart, and maybe you’ll save a buck or two along the way.
First, I’d like to discuss
what is probably the most misunderstood substance in all of the automotive kingdom: Octane.
The technical explanation is this:
the octane number is a measurement of a fuel's resistance to ignition. With
gasoline, this may seem strange, but higher-octane fuel needs more spark energy to ignite
than regular fuel. That is all octane is—a substance that reduces gasoline’s
tendency to ignite (though the octane itself does not take place in the combustion
reaction). It isn't some special additive that makes horsepower or magically cleans out
the engine as you drive.
With that in mind, here's what is happening in a car that needs high-octane fuel: For one,
it may have high compression (some cars built today are inching back up towards 11 or 12:1
compression!). More compression creates more heat and therefore more power. But the down
side is that it creates "hot spots" inside the combustion chamber. These hot
spots might be the edge of a valve, a piece of casting flash, the edge of a piston,
whatever. In some cases, these hot spots get hot enough to ignite the fuel charge without
the spark plug (this is how a diesel works, by the way, which is why knocking is sometimes
called "dieseling"). When you hear a car laboring up a hill knocking away with
the A/C on, that is what is happening inside the engine. Something in the cylinder is hot
enough to ignite the fuel charge prematurely, usually before the piston has reached top
dead center. Needless to say, this is very, very bad for the engine if it continues for a
prolonged period of time.
High-octane fuel can cure this because it
will resist ignition from these hot spots, and will only ignite from the spark, which is
far, far hotter. Supercharged engines, turbocharged engines and heavy towing can also
create additional heat (obviously), which will increase the octane needs of an engine.
There may be some situations where your engine needs more octane (towing) and when it
doesn't (driving in the winter with no A/C and cold ambient temperatures).
A second cause of knocking that high octane can cure is ignition timing. Too much advance
and you get the same problems with hot spots. Modern cars have knock sensors that tell the
engine computer to retard ignition even before the knock becomes audible. The computer
will push ignition up as far as it can without inducing knock, so it is always on the
edge. This is where it is most efficient and where it makes the most power. Using higher
octane allows the computer to dial in the maximum specified amount of timing advance,
making the most power possible.
Now the important thing to realize here is that the octane only allows the engine to make
as much power as it is designed to make. It doesn't magically make a hotter explosion
and extract more power than the engine is designed to generate. It just allows it to run
at maximum output. That means that your 200 horsepower Buick 3800 engine might be making
only 198 horsepower if you run crappy fuel in it. Putting high octane in it will allow it
to make the full 200 horses, but no more. And if there is no knock on the low-grade gas,
you don't have a problem and you're getting all the power there is no matter what. If it
ain't knockin', you don't need the expensive gas. Guys who claim they can feel the
difference are only victims of wishful thinking—the placebo effect.
Although the gas companies will try to tell you otherwise by advertising the cleaners in
the high-octane stuff and not mentioning it on the lower grades, the truth is high-octane
gas doesn't have any cleaner additives that the lower grades don't. It isn't inherently
cleaner running, either. It's exactly the same except that it doesn't detonate early. That's
the only difference!
In some cases, higher octane may even hurt your engine's performance. While I don't
exactly know why, I seem to get better fuel mileage out of my 5.0L Mustang when I use 89
octane instead of 92. I can't detect any difference in performance, but I get about 40
more miles per tankful, which is very noticeable in a car that is lucky to get more than
200-250 out of a tank.
In summary, it is estimated that gas companies derive up to 40% of their profits from
high-octane gas. It doesn't cost much more to make compared to regular, and there are a
lot of fools out there who wrongly believe that they will have some more power or a
cleaner engine in their Cavalier if they use the "good stuff." Untrue, but
marketing and folklore have done their part to ingrain this into the collective conscious
of the motoring public. People think that they're getting something they're not. If your
car needs high octane, it will only let the engine run as well as it can. If you don't
need it, you're only throwing your money away.
And as far as our old Buicks, with compression ratios under 7.5:1, they'll probably run
just fine on a mixture of Aqua-Velva and some Jack Daniels (joking, but they don't
need expensive gas). The old cars don't need the high octane (my '41's Owner's Manual says
to use 72 octane for best performance), and with their weak ignition systems, may even
misfire on high octane. The best gauge is your ear--if it knocks, try going up one step in
octane ratings. See if it improves. If so, don't spend any more on the top grade. If not,
try the top grade. If it still knocks, you've got a bigger problem and should probably be
thinking about looking for a mechanical cause inside the engine, such as carbon deposits
or too much timing advance.
Synthetic lubricants flat-out work better. They're
slipperier, don't carbonize at as low a temperature, don't get as thick at cold
temperatures, don't lose their lubrication properties as they age (not as quickly,
anyway), and they stick better to metal under higher pressures and temperatures than
conventional lubricants. They won't void warranties, won't eat seals and gaskets and don't
cause engine damage because the engine wasn’t broken in on conventional oils first.
I suspect what happened with that guy’s Volkswagen mentioned earlier is that there
was some other defect in the engine that caused the problem—my guess is that his ring
gaps were incorrect. When they heated up and expanded, they locked the pistons in the
cylinders. That’s not at issue here, but it is probably the kind of story that gave
synthetic oils their bad reputation. Very early synthetics, such as the Mobil synthetic
that came out in the early 70s, did cause problems—on street cars. That first
generation synthetic oil was designed for racing only, and as such was completely
unsuitable for cars that were driven daily. Yes, at that time it did eat seals because
racing engines were torn down frequently and it didn’t matter. It didn't have any
detergents or viscosity modifiers. I’m guessing this is where the whole
misunderstanding began. It is important to note that oil manufacturers have long since
resolved these problems and all modern synthetic oils are of extremely high quality.
The issue with not using synthetics initially is to promote
ring seal. On older cars where rings must "break in" over the first 2000-5000
miles, the synthetic actually works too well, limiting the friction between the rings and
the cylinder walls, slowing seating of the rings. Using conventional oils will allow the
rings to break in faster, then you can switch to synthetic. With modern engines, this is
not much of an issue, since their high-tension rings don't need as much breaking in (Mobil
1 synthetic is factory fill on Corvettes, Porsches, Aston-Martin, etc.).
As far as leakage and destroying seals, many people blame synthetic oil for ruining their
gaskets because they don't understand what is happening. Synthetic oils are "more
slippery" than conventional oils, and can squeeze into much smaller spaces because of
their molecular structure (straight chains of carbon rather than clusters). Therefore,
when you switch to synthetic, the synthetic oils will find their way through holes that
conventional oils cannot. This is what causes the leaks, not the oil itself. The gasket
has not been damaged, but holes that already exist that are too small for conventional oil
are large enough for the smaller synthetic molecule to fit through, and you have a leak.
On a new or freshly rebuilt engine, this should not be an issue. However, some older cars
using NOS gaskets or gaskets made of original materials should probably experiment with
various types and manufacturers of oils to see if the oil “seeps” through the
gasket material.
Synthetic oils may also help clean out the
oil passages in your engine because of its ability to get into smaller nooks and crannies.
This may be another cause of leakage—on some cars, the gunk inside the engine might
be the only thing preventing a faulty gasket from leaking. Once that gunk is cleaned out,
the faulty gasket starts to leak. For me, this is not an inconvenience—I’d
rather know where that leak is rather than trust sludge to keep it tight.
Synthetic oils have greater shear strength and a greater affinity for hot metal. This
means that it "clings" to hot engine parts better than conventional oils and
tends to stay on the parts when you shut off the engine rather than draining back into the
pan. They leave a better coating on engine parts after you shut the engine off, and
provide better protection when you first start the engine (this is critical—before
the oil pump can circulate oil, your engine is running on naked bearings). If you’re
one of those guys who likes to fire up the car when it’s cold and rev it up to about
9000 RPM to “warm it up,” the synthetics might help your rings and bearings last
a little longer. It’s far better not to rev it at all and just drive moderately until
it is up to operating temperature, but I digress.
Some manufacturers of synthetic oils claim extended oil change intervals, and while
technically the oil itself doesn't wear out, it does get dirty, and the only way to get
those contaminants out of your engine is to change the oil. Therefore, I don't go more
than 3-4000 miles between changes on my cars, even though they all use Mobil 1. As someone
who over-engineers everything I do, it's just peace of mind.
Also, I should point out that any oil changed regularly will make your engine last
virtually forever, especially these low-speed Buick engines. The synthetic is probably
overkill. Like I said, I like the peace of mind they offer, so I use them in all my
cars--including the Buick when it is done. I used to race my Mustang, so it was subject to
high-RPM, high-temperature operation where the synthetic would make a difference. I use it
in our two Mazdas because they are high-winding DOHC 4-cylinders. I put it in my mother's
cars because she frequently drives very short distances without the engine fully warmed,
and the synthetic's cold-flow properties will prevent any real damage to the motor. I use
it in the winter because it flows better at low temperatures and lubricates the engine
faster, in addition to the aforementioned "clinging" to the motor parts (Mobil 1
offers a 0W-30 oil that I use between November and March). But if you're good with
maintenance, it is probably more than you need. If you're like me, though, the added peace
of mind it brings is worth the additional cost.
My last point on synthetic oils:
they are 100% compatible with conventional oils. You can mix them in the same crankcase
fill if you want, and if you use conventional oil and switch to synthetic, you can
definitely switch back with no problems other than those I mentioned above. For mixing and
switching purposes, they are the exact same thing.
When
our collector cars were built (most of them, anyway), leaded gas was all that was
available. In the mid-70s, the EPA started phasing lead out of gasoline because lead
molecules cause brain damage. I guess that's a good enough reason to get rid of it.
Many experts predicted that the
elimination of lead would cause instant and catastrophic damage to the valves and valve
seats of cars made before 1973 or so, which didn’t have hardened valve seats. The
theory is that the lead lubricates the valves and “cushions” the valve seat as
the valves snap closed. While this is probably true, the past 15-20 years of reduced lead
gasoline has demonstrated that the damage to valve seats is not as severe as predicted. If
you use your car in severe conditions (towing a trailer, racing, in hot environments),
then the valve seats may start to recede without lead. But if it is just a fair weather
driver, damage is unlikely to show itself for the life of the engine.
Again, if you’re like me, and
you like the peace of mind that modern advances bring to older iron, then have hardened
valve seats installed in your car’s engine. I don’t recommend running out and
doing it to an engine that has a lot of life left in it, but if you’re doing a
rebuild anyway, they only cost a few bucks extra at the machine shop. In that case, I
think it is a very wise investment.
The one place the lead myth has
any truth is when you’re talking about muscle cars of the late 60s. Lead was also an
octane booster (see the discussion on Octane, above), and many
muscle cars with high-compression engines need more octane than current pump fuels offer.
In these situations there are several options: add an over-the-counter octane booster in
every tank of gas, de-tune the engine or rebuild the engine with lower compression
pistons. These cars typically don’t suffer the same valve seat recession problems
that older cars do, but the lead was definitely a factor in the design of the engine, and
steps should be taken to remedy the situation instead of limping along on a half-measure.
Pulling out some timing might help in the short run, but in the long run, invest in a
permanent solution such as lowering the compression ratio (you can usually pick up the
lost horsepower in other ways that will still allow you to run 92-94 octane pump gas).
I hope that at least a few people
will read this and realize that they can save money at the gas pump and no longer have to
worry about damage to their old engines. And if you see a guy at the pump next to you
pumping the expensive gas into his beater, let him know the truth. He'll probably thank
you for it.
See you next month.
E-mail me at
toolman8@sbcglobal.net
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