Hi, all.
I'm trying to help a friend with his boat, which has an Evinrude 115 V4 (115793S) supposedly a 1975 or 1976 engine. The symptom is it overheats at much above idle. Meaning, if you idle through canals and no-wake zones, it's fine, but past that if you open it past about half throttle, the overheat switch will trip within a couple of minutes necessitating an immediate shutdown. So far, this is what I know:
- the water pump is only a couple of years old
- the right side cylinder head seems new(er), it's bare aluminum where the left cylinder head is painted black like the rest of the engine
- the overheat switch has been removed and tested, it closes at about 214F and re-opens around 170F.
- the thermostat and Vernatherm components have been checked and are OK.
- on land, with muffs on the water inlets and the engine around idle, the engine seems to draw in water OK and the thermostat is obviously cycling open and closed.
one thing I noticed when running on the trailer is that when the hot water is being dumped, it seems "fizzy" not like soda but with fine bubbles in it. I don't have much experience with marine engines, but plenty with automotive engines and my first thought is that overheating under load combined with bubbles in coolant = bad head gasket. At this point the only thing I can think of other than a bad head gasket is an obstruction in the water jacket. either case, the heads will probably have to be removed.
am I on the right track?
Thank you.
edit: to add, the water pump has been opened and checked, the impeller fans out OK and there's no sign of any burning or material transfer.
I'm trying to help a friend with his boat, which has an Evinrude 115 V4 (115793S) supposedly a 1975 or 1976 engine. The symptom is it overheats at much above idle. Meaning, if you idle through canals and no-wake zones, it's fine, but past that if you open it past about half throttle, the overheat switch will trip within a couple of minutes necessitating an immediate shutdown. So far, this is what I know:
- the water pump is only a couple of years old
- the right side cylinder head seems new(er), it's bare aluminum where the left cylinder head is painted black like the rest of the engine
- the overheat switch has been removed and tested, it closes at about 214F and re-opens around 170F.
- the thermostat and Vernatherm components have been checked and are OK.
- on land, with muffs on the water inlets and the engine around idle, the engine seems to draw in water OK and the thermostat is obviously cycling open and closed.
one thing I noticed when running on the trailer is that when the hot water is being dumped, it seems "fizzy" not like soda but with fine bubbles in it. I don't have much experience with marine engines, but plenty with automotive engines and my first thought is that overheating under load combined with bubbles in coolant = bad head gasket. At this point the only thing I can think of other than a bad head gasket is an obstruction in the water jacket. either case, the heads will probably have to be removed.
am I on the right track?
Thank you.
edit: to add, the water pump has been opened and checked, the impeller fans out OK and there's no sign of any burning or material transfer.
