i read a study which said 30 percent synth offers the same benefits as full synth. i dont know anything about cooling better, but it probably would a little.

there have been a lot of advances over the years to provide the synth with the same properties as dino-juice, so oil leaks aren't a problem, but if you have any leaks, and you switch to synth, i would not be surprised if they got worse. seals have gotten better over the years too...

also.. do not put in any oil additives with synth.. ever. it may not react well.

i've had good and bad experiences with synth oil, and have used different brands, and talked to reps from valvoline and mobile. i run valvoline or havoline. when my engine seats, i plan on running 2 quarts of valvoline synth/4 quarts havoline dino. (valvoline and havoline are the same oil)