Tommy in FLL
Seaman Apprentice
- Joined
- Apr 10, 2009
- Messages
- 44
First of all, hello.
I recently bought from a neighbor a 16 foot Larson All-American with a '96 Yamaha C85 motor. Came with a trailer, all in average condition: $1800 for everything.
Problem: the engine overheats if run at high power for any length of time.
-So far, I have checked the overheat sensor by putting it in a pan of water on the stove, and checked the temperature that it comes on. It is right in the range that the Yamaha service manual says, so I think it is correct. Second, I changed the thermostat. It looked a bit corroded, so I changed it to no avail. Then, convinced that I had a blown head gasket [with the thermostat cover removed, when the engine was running there was exhaust coming from the coolant passage], I changed the head gasket. When I pulled the head, I noticed A LOT of corrosion. It looked like the passages were nearly blocked with white/orange gooey crud. I scraped out as much of it as I could, and the passages were way better when I put the head gasket back on. After all this, the engine still tended to overheat, even with the thermostat REMOVED. I can run for a while at 3000 rpm and get on the plane, but if I go over this speed, the overheat siren comes on fairly quickly.
The PO [previous owner] told me that he had just replaced the impeller. Indeed, when I first looked at the boat, the lower unit was removed. Later, he put it back on and hooked up the hose to the water ports and the engine appears to be pumping water very well. The little squirter on the side of the engine always sprays a healthy stream of water, even at idle.
One of the things I noticed when I had the head gasket off was that the side of one of the cylinder barrels appeared "chipped", like a section had actually corroded right off. This dent in the outside of the barrel [water side] was filled in with Marinetex or maybe JB Weld. It appeared well done, but it blocked the coolant passage to a small extent. I filed it back a bit, but it makes me wonder.
Overall, the engine runs almost perfect otherwise. No shifting problems, no starting problems, idles perfectly, uses very little fuel, and there is no bogging or hesitation from dead idle to full throttle. It's even quite clean.
Hmm. Any ideas?
Thanx in Advance!
T
I recently bought from a neighbor a 16 foot Larson All-American with a '96 Yamaha C85 motor. Came with a trailer, all in average condition: $1800 for everything.
Problem: the engine overheats if run at high power for any length of time.
-So far, I have checked the overheat sensor by putting it in a pan of water on the stove, and checked the temperature that it comes on. It is right in the range that the Yamaha service manual says, so I think it is correct. Second, I changed the thermostat. It looked a bit corroded, so I changed it to no avail. Then, convinced that I had a blown head gasket [with the thermostat cover removed, when the engine was running there was exhaust coming from the coolant passage], I changed the head gasket. When I pulled the head, I noticed A LOT of corrosion. It looked like the passages were nearly blocked with white/orange gooey crud. I scraped out as much of it as I could, and the passages were way better when I put the head gasket back on. After all this, the engine still tended to overheat, even with the thermostat REMOVED. I can run for a while at 3000 rpm and get on the plane, but if I go over this speed, the overheat siren comes on fairly quickly.
The PO [previous owner] told me that he had just replaced the impeller. Indeed, when I first looked at the boat, the lower unit was removed. Later, he put it back on and hooked up the hose to the water ports and the engine appears to be pumping water very well. The little squirter on the side of the engine always sprays a healthy stream of water, even at idle.
One of the things I noticed when I had the head gasket off was that the side of one of the cylinder barrels appeared "chipped", like a section had actually corroded right off. This dent in the outside of the barrel [water side] was filled in with Marinetex or maybe JB Weld. It appeared well done, but it blocked the coolant passage to a small extent. I filed it back a bit, but it makes me wonder.
Overall, the engine runs almost perfect otherwise. No shifting problems, no starting problems, idles perfectly, uses very little fuel, and there is no bogging or hesitation from dead idle to full throttle. It's even quite clean.
Hmm. Any ideas?
Thanx in Advance!
T