Currently using synthetic 10W-30 PCMO in garden tractor. Considering using HDEO, as sometimes operate engine 3-4 hours at a time in warm weather. HDEO is often recommended here for this application, and its higher viscosity indeed seems well suited for extreme heat. However, are there any drawbacks to exposing a small gasoline engine to an HDEO additive package? Possible risk of increased internal corrosion? Perhaps during the off-season? Other concerns or possible drawbacks?