We noticed we had some antifreeze leaking from the overflow tube on top of the heat exchanger by the radiator cap.
We have an accumulator tank because we have our hot water heater connected to or Beta 38 hp motor. The hot water heater is higher than the motor.
We do use the radiator cap on the motor for filling or check the antifreeze coolant through the cap on the motor. We decided to close this tube with a piece of hose bent over its self with a clamp.
It is possible that the pressure cap on your pressure tank (you called it an accumulator tank) holds more pressure than the one on the heat exchanger tank. This could be causing the leakage and simply swopping the caps around will then fix the issue.
