Many thanks for all the excellent advise. I soaked the slightly dirty heat exchanger for 10 min in
Muriatic Acid and 25% water. The engine now runs about 10 degrees cooler.
2,000 rpm at 175 deg 6 knts
2,500 rpm at 180 deg 6.5 knts
3,000 rpm at 185/190 deg 7.2 knts
I intend to run about 2,500 to 2,700 as cruising RPM, It is nice to have some RPM in the bank.
Will look into maybe changing up to a 14" 4-236 heat exchanger.
regards
Mark
Cal 48 Wainui
Ventura