There is nothing special about Briggs or Kohler SAE 30. 10w30 will be the same viscosity at operating temperature as an SAE 30 oil as well. I wouldn't trust AI to give good advice about oil, I've even had it give me incorrect info about oil capacity before. I'd try a 15w40 heavy duty oil like Rotella or Valvoline, or any good 20w50 and see if that helps. I've had good results using those two grades in older equipment.
I topped it off with Valvoline 20w50 today and it’s visibly much thicker than the 30 when pouring out of the bottle. We’ll see what happens after I run it.
Just curious, are you sure what model you have? A K17 Series II is a horizontal shaft engine. Can you find the actual model number on the block or shroud?
Looking online, the K series engines were predominantly horizontal shafts, the only vertical models were rather rare from back in the 60’s.
What you describe about less consumption for the first hour makes perfect sense. After an hour the engine and oil are hotter than at startup. With those higher temps, metal expands and some internal clearances can grow. The hotter oil is thinner and can more easily escape past worn rings and cylinder walls. It can take a while for the oil to get up to full temperature, too.
The SAE 30 oil stays thicker a bit longer than 10w-30 but ends up the same thickness as 10w-30 once the oil is hot. The SAE 30 is thicker at room temperature so takes more heat to get to get thin. After you mow long enough to get the SAE 30 good and hot, it will probably burn at the same rate as 10w-30.
The main thing is to keep the oil full. The weight rating isn't going to make a difference in terms of wear or longevity so long as you don't let it run low.
I topped it off with Valvoline 20w50 today and it’s visibly much thicker than the 30 when pouring out of the bottle. We’ll see what happens after I run it.
