I have a riding lawn tractor with a 460 cc Kohler engine. The manual says to change the oil every year. This year, I noticed the price of conventional and synthetic oil was about the same, so I wondered if I could buy synthetic oil and go perhaps two years between oil changes. Would that be wise? Are the any pitfalls in using synthetic oil in a lawn tractor?
One of the big problems, especially for seldom-used (and if you are not running a lwn-care business, your lawn tractor qualifies, in hours per year, even if you mow and blow snow with it) is that without an oil change, you are building up condensed water and various breakdown products, and storing them in the engine for a long time.
As an opinion, I prefer the model of changing the oil on seasonal equipment just before you put it away for the off-season, so the crud is not sitting in the motor while the motor sits. For higher-hassle than most of us want to put up with, you can store it filled with a storage oil and replace that before running it in the next season; I don't do that, but I have manuals for some old military equipment, and they did that.
In any case, that is the primary reason that very long (time) intervals for oil changes are a bad idea.
Oil life is typically measured with distance or time
1 year on a tractor for oil life of a synthetic is a reasonable expectation.
Mobile makes a claim about their synthetic oil stating that it will last up to 10,000 miles rather than interval that most mechanics claim for a synthetic at 5,000 miles. Most manufacturers state that 12 months is the limit for their products.
Going 24 months between oil changes does not seem reasonable as it is well beyond manufacturer suggested intervals. Keep in mind that many manufacturers have increased their oil lifespans from 3,000 miles to 5,000 and some have recently stated 10,000. I do not see this 12 month interval as a revenue ploy. Being able to state a greater interval can drive sales just has the increased mileage has.
In my opinion 24 months is not a reasonable expectation.