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Hello-
New to the forum. I own a '96 85 horsepower Yamaha outboard which has a problem with the overheat warning siren coming on if I run it at about 3000 rpm or above for about 30 seconds. The engine runs flawlessly otherwise- it starts on the first turn of the key, accelerates perfectly, and it appears to be pumping water fine.
I bought the boat from a neighbor, and I got it, boat and trailer for $1800 in average condition, so I did decent on the deal overall. I use it to tool around the canals [all are "wake-speed" due to manatees] around town on sunny days, friends and beer on board. The boat will run all day long, trouble-free like this, and barely burn more than 2 gallons per hour at 1200 rpm, making about 5 knots.
At the same time, there are areas where one can "open her up", and I'd like to but the warning siren comes on.
I suspected blown head gasket, and me and the previous owner pulled the head. Sure enough, the gasket looked like it was burned in one small area, and we replace it. I noticed on one of the cylinder barrels that the outside surface [the water jacket side] had a chip missing, probably due to corrosion, that had been repaired with what appears to be Marine-tex. The gasket area that corresponded to this wasn't burned. I did not do a compression check.
The water jackets were full of crud, most of which we were able to dig out with a thin tool. It appeared to be some sort of clear/brownish glop....again, the motor pumps water just fine, and the previous owner changed the impeller himself.
I tested the overheat sensor in a pan of hot water, and it goes off at about the correct temperature, so I'm fairly certain that it is operating correctly. What perplexes me is that when it goes off, if I remove the engine cover and place my hand on top of the thermostat....it is hot to the touch, but certainly doesn't burn my hand! I am running the motor without the thermostat in place currently.
I have an infra-red pyrometer, but how do I use it? What point do I point it at on the engine, and what should it read?
Does the lack of thermostat cause the engine to run hotter?
Any thoughts as to a connection between the ignition computer and an errant overheat signal?
Thanx in advance!
T
New to the forum. I own a '96 85 horsepower Yamaha outboard which has a problem with the overheat warning siren coming on if I run it at about 3000 rpm or above for about 30 seconds. The engine runs flawlessly otherwise- it starts on the first turn of the key, accelerates perfectly, and it appears to be pumping water fine.
I bought the boat from a neighbor, and I got it, boat and trailer for $1800 in average condition, so I did decent on the deal overall. I use it to tool around the canals [all are "wake-speed" due to manatees] around town on sunny days, friends and beer on board. The boat will run all day long, trouble-free like this, and barely burn more than 2 gallons per hour at 1200 rpm, making about 5 knots.
At the same time, there are areas where one can "open her up", and I'd like to but the warning siren comes on.
I suspected blown head gasket, and me and the previous owner pulled the head. Sure enough, the gasket looked like it was burned in one small area, and we replace it. I noticed on one of the cylinder barrels that the outside surface [the water jacket side] had a chip missing, probably due to corrosion, that had been repaired with what appears to be Marine-tex. The gasket area that corresponded to this wasn't burned. I did not do a compression check.
The water jackets were full of crud, most of which we were able to dig out with a thin tool. It appeared to be some sort of clear/brownish glop....again, the motor pumps water just fine, and the previous owner changed the impeller himself.
I tested the overheat sensor in a pan of hot water, and it goes off at about the correct temperature, so I'm fairly certain that it is operating correctly. What perplexes me is that when it goes off, if I remove the engine cover and place my hand on top of the thermostat....it is hot to the touch, but certainly doesn't burn my hand! I am running the motor without the thermostat in place currently.
I have an infra-red pyrometer, but how do I use it? What point do I point it at on the engine, and what should it read?
Does the lack of thermostat cause the engine to run hotter?
Any thoughts as to a connection between the ignition computer and an errant overheat signal?
Thanx in advance!
T
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