Mods, I didn't see a boat section so please move as needed.
Here we go. I have a boat with twin 350ci engines. A few weeks ago my port motor started running hot. It has NO thermostat in it. By running hot I mean it will slowly creep up to 200+ over 3-4 miles at cruising speed (3250-3300 rpm). So I start investigating. The engines are fresh water cooled. This winter I replaced the raw water pump impeller, cleaned the oil cooler, boiled out the heat exchanger. I pulled the raw water lines and have good water flowing all the way to the the risers (no aeration in the water). The risers are only on their 3rd season. coolant levels are good. Finally after not finding any obvious problems, I thought maybe I was chasing a ghost. So I swapped the temp sensors port and starboard. Now, the port motor still does the same thing and now the starboard is creeping up too. That motor has a thermostat and never ran above 160 until I swapped the sensors. Now, thinking the elctrical might have a problem causing a fuck up in the sensors I went out and shot the thermostat housing with a laser temp gauge. My gauges were right. Now both motors are getting hot. I dove down to check the intakes and both are clear. I have good raw water flow. WTF??? I am running out of ideas. The only thing I can think of is my risers are failing after only 2 years. Any thoughts would be helpful.
Here we go. I have a boat with twin 350ci engines. A few weeks ago my port motor started running hot. It has NO thermostat in it. By running hot I mean it will slowly creep up to 200+ over 3-4 miles at cruising speed (3250-3300 rpm). So I start investigating. The engines are fresh water cooled. This winter I replaced the raw water pump impeller, cleaned the oil cooler, boiled out the heat exchanger. I pulled the raw water lines and have good water flowing all the way to the the risers (no aeration in the water). The risers are only on their 3rd season. coolant levels are good. Finally after not finding any obvious problems, I thought maybe I was chasing a ghost. So I swapped the temp sensors port and starboard. Now, the port motor still does the same thing and now the starboard is creeping up too. That motor has a thermostat and never ran above 160 until I swapped the sensors. Now, thinking the elctrical might have a problem causing a fuck up in the sensors I went out and shot the thermostat housing with a laser temp gauge. My gauges were right. Now both motors are getting hot. I dove down to check the intakes and both are clear. I have good raw water flow. WTF??? I am running out of ideas. The only thing I can think of is my risers are failing after only 2 years. Any thoughts would be helpful.
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