For closed cooling I'd definitely go 160, maybe even warmer. I ended up putting 170* thermostats in my closed cooling Merc 454s to get the temps up higher when cruising slow (they run 170 - 175* at slow cruise now instead of 160 - 168*). Temps on plane hardly changed compared to the 160* t-stats (went from about 175 - 180* to 178 - 182*), but the temperature swing from running slow to fast is smaller now. Generally warmer is more efficient and will idle better as long as it's not hot enough to cause any issues.
Only downside I've found to the warmer thermostats is a little more carb smell after shutdown (working on ventilation changes to eliminate that).
For closed cooling I'd definitely go 160, maybe even warmer. I ended up putting 170* thermostats in my closed cooling Merc 454s to get the temps up higher when cruising slow (they run 170 - 175* at slow cruise now instead of 160 - 168*). Temps on plane hardly changed compared to the 160* t-stats (went from about 175 - 180* to 178 - 182*), but the temperature swing from running slow to fast is smaller now. Generally warmer is more efficient and will idle better as long as it's not hot enough to cause any issues.
Only downside I've found to the warmer thermostats is a little more carb smell after shutdown (working on ventilation changes to eliminate that).