Oil temp will easily exceed water temp if you are using block filler. With 1/2 fill, my oil temp sees 212 while my water temp is at 180. - 10W30 Royal Purple full synthetic race oil. Per Royal Purple, most run too low oil temps - claims their synthetic will easily handle 250+ temps with no ill effects. Think they were mostly referring to expunging water from the crankcase. At idle start up I am looking at 70 psi. At idle and 212 oil temp I am looking at about 25 psi.( makes me a little nervous) Yes, it has been my experience that synthetics are more prone to leaks. I switch to 10W40 in real hot weather.