If the coolant is only 10į F cooler than the oil, their will be very little cooling going on. OEMís typically fit these for their heater properties . . . getting the engine up to operating temp quickly reduces emissions. I try to call them water-to-oil heat exchangers or more simply, oil heaters.
Yup. And that's what most normally aspirated OEM street car installations seem to use it for. Two examples I know of:
ST184 Toyota Celica: keep the oil warm in an under-worked 5S-FE. Also makes the engine unkillable on track days (if rather slow).
P71 (police interceptor) Ford Crown Vic: keep the oil warm when idling for long periods in cold temperatures - common in police and taxi use.
In my air cooled engine experience, I've found oil temperature to correlate more with BMEP than anything else - basically, the hotter the pistons get, the more heat goes into the oil.
In the case of the 2ZZ-GE Elise, we have problems in both extremes: The engine is very lightly loaded - it came in small minivans (Toyota Matrix), and even in a Celica it's pushing around a car with 1/3 more frontal area and 500 lbs more curb weight than an Elige. That makes an Elise slow to warm up. On the other end of the scale, Lotus drivers persist in taking their cars on race tracks, which means that the engine is making 100% of available power something like 50% of the time.
An oil cooler that heats the oil when it's cooler than the water, and cools it when hotter is exactly what we need. That's also what Lotus put on the original 111R. For some reason, they decided that the USA was like the Persian gulf and race cars in its oil cooling requirements.
Street driven US Eliges would have been much better served with the same package UK/EU Eliges came with.