"Trevor Jones" wrote in message
...
Artemia Salina wrote:

Dumb question I guess, but why do engine manufacturers make
valve stems that are filled with sodium (I think only exhaust
valves are sodium filled). Is it a heat expansion issue?

Thanks.

Better heat conductivity aids in transferring the heat away from the
valve head.

Curious that aluminum and copper both have a much higher thermal
conductivity than sodium
http://web.mit.edu/3.091/www/pt/pert14.html

But I have a feeling that the relatively low melting point of sodium(371K)
with copper(1356K) has something to do with transfering heat better. I
dunno.
http://web.mit.edu/3.091/www/pt/pert12.html
the sodium would be a liquid at internal engine temperatures.