My dohc bike has a plate on it, that currently has a rubber hose from input to output. I assume I could replace the rubber hose with an appropriate oil cooler/radiator.
I would think (strictly my opinion) that anything that reduces the oil temperature is a good thing, but I would be concerned if the oil never comes up to "operating temperature". That being the point where the viscosity of the oil does the best job of keeping the engine internals properly lubricated and contaminants and dirt off of the moving parts. Oil that gets too hot is no good, and oil that's too cold may not be good either.
If you were in a temperate climate, say south of the Mason Dixon line in the US, an oil cooler might be a good idea. North of that line, it would help from late spring to early fall. It might also be possible to put in a bypass to keep the engine oil temperature in the optimum range. This sounds like an interesting engineering exercise. Rigging up an oil temperature gauge might be a problem, but not impossible. I've seen cars use 2 sensors (oil pressure, oil temperature) off of a T junction in place of the oil pressure switch sender.
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
I installed an oil cooler on my '79 CB750K, with an oil temperature gauge, and a Perma Cool automatic thermostat. I bought a radiator off of e-Bay (from a Honda CB900); the thermostat was new, from the Internet; the adapter was new, from a machine shop now out of business -- it also converted to a spin-on filter... Love it!
Oil needs to reach 180 F to perform optimally. My thermostat opens at 180 F, sending 95% of the oil to the cooler; below 180 F, it sends 10% to the radiator, to prevent thermal shock, and foaming, with the other 90% going back to the engine. My temperature gauge measures oil coming out of the filter.
I used high pressure, T-bolt clamps as the worm gear clamps (common hose clamp type) let oil blow by, under pressure. The T-bolt clamps are a little more money, but they won't leak, unless the hose ruptures...
I made a mounting bracket out of aluminum bar stock (spray painted black, to blend in with the frame tubes), purchased from a local DIY store. This was secured to the two down-rod's of the frame, with U-bolts, and locking nylon nuts. The thermostat was placed inline, between the adapter, and the radiator.
Teflon/plummer's tape will NOT hold! Do NOT use Teflon/plummer's tape to seal the hose barbs, nuts, whatever... Use a hydraulic hose fitting sealant -- it is made for high pressure, high temperature, and exposure to oils. Teflon tape will work for a while, then, with usage, it will begin to leak, and it will continue to leak. This will deposit oil in the pathway of your rear tire as you are riding!!!
I ran the system in Iowa, on a long highway road trip, 60 MPH, for 4+ hours, with an air temperature of lower-90's. The oil temperature, coming out of the engine, before it entered the radiator, was an average of 210 F. We were riding two-up, with loaded saddlebags and trunk.
On our way home, we ran the same load, but in low-80's temperatures, and the radiator was bypassed due to leakage problems. The oil temperature registered around 250 F, the entire trip home.
Dino oil breaks down at 250 F, and above, forming sludge/carbon deposits. Below 180 F, oil will not suspend crud and sediments, and it will not boil off combustion byproducts, either. You need your oil to be between 180 F, and 250 F. Ideally, you want your engine's oil to run at a constant 180 F: the cooler the oil, the longer it will last.
I discovered that even with the thermostat, my engine oil will run too cool when the air temperatures are below 55 F, roughly. Even running it at 60 MPH, the oil barely made it to 180 F (at slower speeds, it never reached 180 F), so when the temperatures drop below 60 F, it may be necessary to cover the radiator, to allow it to reach 180 F.
Synthetic oils last 10,000-20,000 miles, before you need to change them. They won't break down from heat until they reach 300 F+. They remain thin for easy starts even at -20 F. They retain film strength on bearings after months of sitting, without starting. Even with the radiator, and thermostat, I will be switching to full synthetic. I hope to extend the life of the engine (21k miles currently) to far beyond the normal 70k miles, before it needs an overhaul, or other service. YMMV.
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII