coolant drain

I want to drain the coolant from both engines. I am looking for some suggestions on what else you would do if you are spending the time and money to do the change and flush. Impellers would be an example. Would you look at changing the impellers if you were unsure the last time they were...

I'm having a problem with overheating and the engines going into "safe mode". It only happens over time when running pretty well full rpms. The temp gauges read 175 when it drops to guardian mode. I live 100 miles from any mercruiser dealer that can work on my boat. I replaced the water...