I bought a used rider this Spring. It's a 16.5HP OHV Briggs. The manual states SAE30 for temps above 40 degrees F, or Synthetic 10W30 for temps 0-100. I did the first oil change with 10W30 synthetic (Castrol Syntec on sale). I maybe ran it 5 hrs (tops), and plan to change again this Fall before putting it away. I will leave the filter on there, but wish to change the oil again in order to clean it out (I also need to change the diptube seal, and put a quick-change valve/plug on there). Does it really need Synthetic, or will a blend or dino do fine? It's a $300 special that I use more as a toy. It just seems silly to use $8-10 oil for the old rider.