It's called an oil cooler for a reason, as it is there to cool the oil and help it survive high engine temps such as when you drive through a hot desert using high engine power output (where the engine generates the most heat).
The cooling fins on the engine do the bulk of the engine cooling by far. Both devices need air flow for them to do their job.
Unless the engine was designed to be cooled by oil, an oil cooler is for keeping the oil in a proper state of health, and only indirectly aids engine longevity. An oil cooler also needs a corresponding thermostat to do it's job properly, or there is risk of over-cooling the oil below its optimum working temperature. Short rides may never see the oil temp get high enough to even use the oil cooler, leaving it just so much added weight and unnecessary complexity. Over-cooled oil does not lubricate the engine properly.
The stock SOHC4 doesn't need an oil cooler for street use. If you have made special mods or use it in an abnormal way, there can be some benefits to an added oil cooler.
I'm convinced the popularity of oil coolers is largely based on myth, conjecture, and wishful thinking, rather than science or demonstrated need. The other reason has to do with "looking" like something related to a track vehicle that actually has a need based on the environment it is used within. Street bikes rarely, if ever, meet those conditions.
There is some rationale that says it might extend the useful life of the oil, by keeping the oil below breakdown temps on long, hot, loaded down rides. But, economically it makes more sense to me to simply change the oil at the normal recommended service interval.
I have a Lockhart oil cooler that came on one of my 750 bikes. It's an F model that had its engine replaced with a K motor. Anyway, I'll eventually move that thing over to a cafe/custom style buildup to enhance it's sales appeal. Every bit of eye candy helps for that genre.
If the engine isn't making more heat than stock, or routinely making more power than stock, the oil cooler is just added weight, a conversation piece, and sales tool.
Previously in this thread, the point was made about the oil cooler's location upstream from the engine cooling fins. Raising the temperature of the air passing over the engine cooling fins reduces their ability to transfer heat away from the engine. I question why one would want to diminish effectiveness of the engine's primary cooling system in such a way.
IMO
Cheers,
