I have a 20 hp Kohler command series. The unit is used for carpet cleaning inside a chevy express van.All the doors are open when in use. I was using 10-30 full synth oil but had leak in the main seal at the shaft. Repair was made and was told to run at 3600 rpms but the water get to hot at 260 temp. the unit runs better at 29-3000 rpms. I have now switched to 15-40 shell oil hope that helps Any info on oil would help. and I.m located in Ft. Myers Fl 98 deg. and high humidity . Thank you jz.