Jams - You need a certain amount of heat to boil off water condensate in your
oil. Your
oil/motor will build up sludge if it is too cool, to much. Synthetics help this, but IMHO it is more important to watch your
oil temp. As for water temp. the cooler the better by in large unless it's so cool that your oil temp. goes south. And yes your right. the A/F ratio can lean out due to cooling or even iceing on/in your intake manifold. (depends on type of manifold your using) In most engines 180 to 200 degrees coolant temp. is just about right.
cobrashock