I've never had one performance problem with TF, my saws just screeeam with the stuff!!.. I buy the 4 stroke 92oct fuel and add my own oil(stihl gray bottle, 50:1)
The problem with them ol mills is oil pressure, tons of hours and lack of Maintenace equals to big tolerances everywhere inside. Myself I would keep the 15w40 unless you know oil pressure is adequate.
I have 3 standard Schumacher maintainer/ chargers 1.5A on my subcompact, lawnmowers and one on a 1000cca battery in my plow truck, been working great for many many years. I can start any of them and they spin over like new
The gray bottle Stihl Ultra synthetic despite all the miss informed info on LoserTube is good stuff, my saw has yet to blow up or seize a crank or piston, it just keeps cutting and cutting.
FRAM says it filters the same or better but i would still rather have the old media set up, personally I don't think it does.
Just a way to cheapen out and get the same money!!
Iseki calls for a 5w30 or 10w30
And there's no known cross ref for the oem engine and Hyd. on the 1723 and 1725, there is for the older models but not the new 23/25 series.
The Iseki OEM engine oil filter is made by Denso there a quality filter.
Any synthetic engine oil will be fine Amsoil 10w30 is a great choice. Hyd/trans/front end id stick with the 10w30 821XL, these tractors have no oil cooler so the oil gets hot and actually the 821 IS a quality fluid(reformulated semi syn.)
You need to be careful at least in a snowmobile application, running it hard from ice cold you can get cold seizing, the piston expands faster then the boar.
I always give 2 smokes a few minutes before WOT