I have an old (circa 1988) Mariner 2 stroke 75hp clamshell and am having problems with an overheat. I've been all through the cooling and warning systems (see my previous thread here
) and come to the conclusion that it is a genuine overheat problem, having replaced all of the main cooling parts, checked flows, checked the alarm sensor etc. and opened up the engine to check cooling paths are clear. When I opened up the exhaust cover plate, however, I found deposits on the middle cylinder piston wall where it is exposed to the exhaust manifold.
There is a dark patch on the lower piston ring, but no significant deposits between rings, which made me think it wasn't blowing past the rings.
Anybody know what is likely to cause this sort of thing? I am sure I read somewhere that if it was running lean on a cylinder, then that could lead to increased exhaust temperatures, which would then cause the overheat and oil to burn on the cylinder. Can anybody shed any light on this?
Unfortunately there appears to be some piston damage, and I'd guess there would be cylinder damage also but can't easily inspect that. I do not know if this is significant damage or not. Compression is equal on all cylinders at pretty much 100psi and it starts, runs and re-starts really well. I can't tell if it is down on power at all as it's probably been a problem since I had it. Can anyone tell me if the piston will need replaced or if it will require a re-bore?
I am really torn with this problem. I need the engine to be reliable as I'm planning trips to the Isle of Mann and Irish sea so will be a long way from shore if there is a problem. I don't know if a 26 year old engine is worth repairing, waiting for the next failure, but also not sure if the hull is worth re-powering.
Any comments on the fault, fix or engine quandry greatly accepted.