Synthetics run cooler. That is no big news. I have been aware of it for many years. It's just the first time I have checked the difference with anything more than a vehicles dash guages. Vehicle instruments have shown lowered operating temps as well as increased idle speeds when switching to synthetics in the past. I am going to try to install an oil temp gauge on the mower, but an IR thermometer was used in this case. Exmark Metro 36", Kawasaki 12.5 FB460V. A proper comparison would have been between a petroleum and a synthetic 30W, however I changed from Castrol 30W to Amsoil 10W40, in a Kawasaki 12.5 and realized a drop of 8 degrees on average, in oil sump temps and block temps at various spots on the engine block. Measurements were taken against the side wall of block well above the oil level and also measured at the bottom of the sump where the oil sits. Mower was warmed up and then used for ten minutes of mowing each time. On the second run with the synthetic oil, a proslide was used to add more strain to the engine. Temps were taken upon completion of mowing for ten minutes and during a couple minute cool down period of idling the engine. Temperatures dropped as much as ten degrees during the cool down in each case, and were 6-10 degrees lower when tested with synthetic, than they were when checked with non synthetic. The mower has over three hundred hours on it. It was not using or leaking oil before. The manuals state that when using a multi viscosity oil, comsumption may increase. I will post back on any difference noted there. I may also put some 30W petroleum back in and take readings at the head and valve area. Rightfully that should then be compared to synthetic 30W. Maybe if I install the oil temp guage I will redo this test with pics and log the readings.