On 06/16/2013 02:40 PM, Richard Lamprey wrote:
> <lamprey.richard@gmail.com>
>
> Greetings to all from Kenya.
>
> Does anyone know what is the minimum cylinder head (coolant)
> temperature for normal operations? The manual gives maximum but no
> minimum, save for warming up to above 50C for takeoff power. I was
> told recently that cylinder head temp should not be too much below
> Oil temp, but not sure about this.
My idea is that all the different materials and shapes in the engine
expand at a different rate when the temperature varies. For optimum
engine live and performance it is best to have the engine wearing its
moving parts against each other at one fixed temperature. If the
temperature varies, the wearing pattern also varies, and you will end up
with an engine wich is "loose" on all temperatures (i.e. loosing its
compression).
Also engine performance rises with rising temperature. Cooling the
engine means robbing its precious combustion energy, so keeping the
engine near its higher end of the temperature scale pays off. (Think
about that one: the reason we burn fuel is to rise the temperature of
the contents of the cylinder so that it expands and produces a force.
The more you take away the heat, the more you take away the driving
force. It is unfortunate that we have to cool at all, one reason why
engineers try to minimize cooling losses when designing efficient
engines. So keep the engine temperatures up, it is one of my secrets of
getting more speed for a liter of fuel).
The only way to achieve this properly is by controlling the amount of
cooling you apply. You can use thermostats or better yet, a movable cowl
flap.
I always maintain a coolant temp of 110C and an oil temp of 115C. This
also has the side advantage that I never reroute too much air for
cooling and this lowers the drag considerably. Some clever souls claim
that for the modern efficient airplanes 40% of the total drag consists
of cooling drag, so it pays off to tinker with the cooling system. (Of
course a thermostat instead of a cowl flap doesn't have this advantage).
Frans
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