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Re: <MISC> Unleaded fuel-help!

Larry, thanks for your $0.02 worth. (It's included at the bottom)

While you may be correct in the USA, let's not get overly focused on the USA.
 Other countries have not had unleaded as long (if they have it yet) and the
method of introduction, specifications, etc are not the same.  The valve seat
erosion problem depends on when the engine was designed.  Some early aluminum
headed engines without hardened inserts are badly affected by the lack of
lubrication provided by the lead.  If you want to know what the current state
of tolerance for unleaded fuel is, I suggest you contact car manufacturers in
countries like South Africa which is going through the introduction of unleaded
fuel now.  The manufactures have compiled lists of engines along with the
tolerance for unleaded which ranges from none through one tank of leaded for
every few tanks of unleaded to no-problem.

Another factor to consider is the average engine size.  USA tends towards
relatively large engines compared with other countries (fuel costs, car prices
and taxes being some of the reasons).  In South Africa many cars have 1100,
1300 and 1600 engines.  These engines tend to work much harder in everyday
driving than do larger engines.  Thus they end up spending much more time under
heavy load.

Countries that have not had unleaded available are now quite far behind the
engine technology curve because almost all engine development in the last
several years has been on unleaded designs.  To make matters worse, the average
car age in those markets is greater than in the USA.  These factors result in a
lot of very old engine designs in everyday usage.  The slow introduction of
unleaded (slow reduction in lead content) in USA allowed most old cars to die a
natural death without the feared problems unless they were racing or towing.
 In countries going cold turkey (unleaded without ANY lead) the old engines
don't do nearly as well.

I would agree that racing or towing will accelerate the wear, also, as I have
said, some engines are not affected, but some are, even in everyday driving.

The mechanism for the erosion of valve seats is as follows: (this is from
distant memory, so facts may vary) the lead provides a layer of protection that
prevents the valve from bonding with the valve seat when it closes.  Without
it, the valve 'sticks' to the valve seat and pulls small amounts of the valve
seat up when it opens.  This happens at a microscopic size and results in tiny
amounts of erosion which eventually leads to valve failure.  This process
depends on the heat of the valve & seat so happens faster at high loads.
 Possibly making small engines more susceptible in everyday situations.

I hope my fact to noise ratio is high enough. Darren may have some relevant
comments, since I know he is in SA now and is experiencing the change in that
country.

Brendon.
'96 M3
'93 MX-5

On Sep 12,  8:13am, Larry Schwarcz wrote:
> Every report I've read says that it's usually not a problem at all to run
> unleaded fuel in a car designed for leaded fuel.  The worry of valve seat
> recession is way overstated.  From what I've heard, you only need to worry
> if you're putting heavy loads on the engine (like towing or racing).  If
> you're only doing normal driving (city and highway), then just use the
> unleaded.
>
> Lets not forget that during it's last few years when leaded fuel was
> available, it had less lead content than *unleaded* did when it was first
> introduced.
>-- End of excerpt from Larry Schwarcz



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