80C or 176 is the normal operating temperature and if the cooling system is working correctly, the temperature should not increase more than 5-8% even at the highest RPM. When you measure 80C on the oil filter, you should measure 50C at the exhaust elbow immediately after the water inlet to the elbow. If it is higher, there is a problem that may be one of the following.
Possible Causes of Overheating:
1. Restricted seawater flow anywhere in the pathway beginning with the seawater entry into the sea chest to the seawater and exhaust exit through the hull.
a. Sea Chest restriction
b. Hose restriction or kink
c. Restriction at the input to the in-line transmission oil cooler, if equipped
d. Failing seawater pump and/or failing seawater impeller
e. Restricted Exhaust Elbow
2. Restricted Coolant water flow
a. Failing coolant water pump
b. Failing Pressure Cap (should be replaced every 2 years)
c. Failing and/or clogged Heat Exchanger
3. Incorrect coolant ratio, but this is usually not a major contributor but will contribute somewhat.
4. Incorrect V-Belt tensioning with the V-Belt turning the coolant water pump
5. Failing Coolant Thermostat (not opening completely)
6. Other engine issues
Do not think that you can measure enough water flow by observing the seawater and exhaust exiting the boat. It will fool you.
David, you may have something here. I have noticed randomly occurring increases of engine temperature up to 220F when running the engine above 2000 RPM. However the temperature does not seem to drop after opening the engine-room door and have not been able to measure any temp in the engine higher the 176F with an infrared thermometer.
Ipanema SM 278
currently in Shelterbay PANAMA