On 21/08/2015 10:50, The Natural Philosopher wrote:
On 21/08/15 10:35, therustyone wrote:


The only time I've noticed a slightly smoother engine (though no
significant improvement in mpg) was when I accidently filled up
with premium diesel instead of standard diesel - and a lot of that
may have been wishful thinking to compensate for paying through the
nose for the "gold plated" fuel :-) I wouldn't have minded quite
so much but I'd driven past loads of garages on my journey, holding
out for the cheapest garage that I happened to pass, and then when
I found a cheap garage I went and used the premium holster instead
of the standard one. Shame they aren't different colours (eg black
versus black with yellow stripes, or something like that).

might depend on the car's sophistication. A quality engine will
monitor pinking and adjust the timing and fuel ratio to optimise
burning with the better quality (petrol anyway) it finds. An older
car will just be set to run on the worst fuel around.

However a car adjusted to run on low grade fuel either by fixed design
or automatically will still run better on better fuel.

No the case for petrol engines.

The octane rating represents resistance to knocking, the higher the
octane the higher the compression and advanced timing.

A side effect is that the fuel burns slower, so good fuel into a car
designed for a poor grade may run snoother but be less efficient and
produce less power.