I have a lawn tractor w/ Chinese single piston motor. Sticker on the motor that says 10w30, but the manual allows for a different range of viscosities to be used based on climate. I've been using Rotella 15w40 T5 because this is a flat tappet motor and at the time I bought the jug, I was aware it contained a decent amount of ZDDP and phosphorus and is also a syn-blen which I prefer. On my latest oil change I didn't have enough left in the jug to fill it, so I wound up having to use about 50% Mobil-1 15w50 (SN-rated) to make up the difference.
I know mixing oils is fine because I have done plenty of research on oil in the past, but my concern is the dilution of the ZDDP by adding the SN-rated oil into the blend. If I recall, the Mobil-1 15w50 still contained a decent amount of anti-wear additives since a lot of folks use that oil in boats and race cars? I am sure this tractor motor has relatively weak valve springs, so I would not think it will matter, but I wanted to get opinions on whether its okay to run this fill for the next 50hrs, or if I should drain it in favor of something that is formulated for sure for flat tappet motors.
Historically, I always liked to use straight 30wt oil in generators, mowers, etc. But the 30wt oils available locally are all conventional and I like to run a syn-blend or full-syn if I can.
Okay, I've over complicated this enough, let's hear the opinions.
I know mixing oils is fine because I have done plenty of research on oil in the past, but my concern is the dilution of the ZDDP by adding the SN-rated oil into the blend. If I recall, the Mobil-1 15w50 still contained a decent amount of anti-wear additives since a lot of folks use that oil in boats and race cars? I am sure this tractor motor has relatively weak valve springs, so I would not think it will matter, but I wanted to get opinions on whether its okay to run this fill for the next 50hrs, or if I should drain it in favor of something that is formulated for sure for flat tappet motors.
Historically, I always liked to use straight 30wt oil in generators, mowers, etc. But the 30wt oils available locally are all conventional and I like to run a syn-blend or full-syn if I can.
Okay, I've over complicated this enough, let's hear the opinions.
Last edited: