Lars, I don't know for sure and it’s been a couple years since doing my research. If my memory is correct from my research a couple of years ago the first cooler was not as good as the second 2 but I may be wrong. My perception of the last 2 is just brand difference. The air delivery to the cooler has changed for sure. I don't know what years these changes happened specifically.
I believe there were 3 different oil coolers or vendors I know of used over the years, maybe more. I did speak to 2 of them directly and the factory just to see if I could use one over the other if I chose to. I determined the answer to that question was yes but went with the same cooler the plane had for reasons above.
I also chose not to have the cooler cleaned after some discussion with two manufacturers. Obviously they are in the business of selling new but a 19 year old cooler, potential silicon, down time, etc made the decision easy based on the cost difference (cleaning or new). I also replaced the Vernatherm Valve and hoses. Second or third time on the Vernatherm over the years and I built a tool out of an old Vernatherm to lap the seat in also. The witness marks on the seat of the valve will tell you if it's sending all the oil to the cooler or not. They make a tool to correct the seat if it's real bad.
Ultimately changing the cooler, hoses and Vernatherm fixed the issue to a point that I feel it's normal and acceptable. I have also done a significant amount of baffle work. The difference is about 5-10 deg's compared to a 2017 on average. Why the newer planes like a 2017 run much cooler than a 1999 I believe is related to the air delivery change not the cooler. Something changed and the only thing I see is the air or where it's taken from. All of this is outside of an overhaul, tear down and inspect, etc. Bearing failure or being on the tight side of spec is one of the causes from lycoming book and phone help.
There are other folks on the list I hope chime in here. I'm a little embarrassed to say how many hours and dollars I have in chasing oil temp's. I feel I've fixed it but ouch! I don't think I would chase 210 deg's on a 110-120 deg day though.
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