Raw water circuit

[Rudderly Confused]

Hi folks,

My question is about the raw water circuit on my Westerbeke W40, in my 1978 Pearson 365 ketch. Sea water runs from the intake sea cock, through the V drive cooler, trans cooler, raw water pump, oil cooler, heat exchanger, and out through the exhaust injection elbow. From the sea cock to the raw water pump inlet the hoses are all 3/4", but from the pump outlet to the injection elbow they are all 5/8". Does anyone know if that is standard practice, or should the hoses stay 3/4" through the entire circuit? I'm in the process of replacing all hoses, most of which look original and definitely need replacement. If I change a few fittings along the way, I can make the entire run 3/4". Does that 1/8" restriction on the back end make a difference in cooling capability? It currently runs a bit hot, according to the gauge, but checking with an IR thermometer shows no problems. The sending unit or gauge may be bad, I haven't gotten that far yet.

[SVJourney]

Mine was 3/4 to the pump and 1/2 after that.  Ran just fine and the needle never went over 180 degrees in thousands of hours of run time.  Getting you heat exchanger serviced at a radiator shop can make a big difference.  Or you can descale it your self if you are feeling bold.