2005 Super Air Nautique 226 - Overheating

Hi Everyone, long time fan, first time post.

We got our lovely used boat in April of this year with only 200 hours on it and after putting a substantial amount of work on it (nearly all hoses, belts, pumps, valves, transmission & impeller replaced), have run into some issues. A couple of times out this summer, the engine started warming up suddenly at idle. Never above 190, but we watch it really carefully anytime we're out there and would shut it down before it got too hot. The issue subsided every time we would put it into gear and cruise along at 5 miles per hour, of which we thought there may be an impeller or water pump issue as the water flow wasn't getting into the engine at idle. This issue would normally only happen when we first put the boat in the water and it wouldn't happen again the rest of the day.

Until last week, I warmed the engine up, ran it at 1500 rpms for a while 10 minutes or so without any issues. I picked up my friends on the dock and once I started going, I saw the temperature rising. I cut the engine when it got to 190 degrees and inspected the engine compartment. It was then that I noticed the coolant reservoir was sucked down and I decided to call it. Turned the engine on and headed to the dock which was only 50 yards away. Pulled the boat onto the trailer and took it home. While flushing the engine, I poured more coolant in, and flushed the engine with my hose (45 psi, good pressure), but the temp still was climbing on me after a minute or so, so I cut it and took it to my mechanic.

The mechanic replaced the impeller which he said looked worn (which is odd considering its only 6 months old). He filled up the coolant and started it up. The exhaust was producing white smoke and the coolant was being sucked dry, which led him to believe that it's either a cracked block or at the very least a blown head gasket, saying that I could have sucked something into the impeller and overheated the engine. He's now saying that he won't know until he opens everything up, which of course is going to cost some dough.

I've been around boats for decades, but this is the first one I've owned and I'm definitely not familiar with boat engines, The mechanic is pushing hard to go through insurance which raises some red flags in my book.

Any insights from the forum would be much appreciated! Thank you!

Find a new mechanic. There are external procedures to check things like this before a tear down. Sounds like this boat is a fresh water cooled 6.0. This makes it really easy to pressurize the cooling system and see where the coolant is going. Also a compression test can find the cylinder in question (if it is leaking in a cylinder) and furthermore a leak down test can tell you where air leaking from the cylinder is. going.

In his defense, it does sound like a bad head gasket or a cracked head (very unlikely a block) and to repair that you will absolutely need to tear the engine apart.

Not really, I presume you can use an automotive head easy since its closed cooled but I haven't been shopping for 6.0 heads ever in my life. I would get in touch with a machine shop that does lots of work on GM LS style engines if you do need to buy parts, PCM will likely charge through the roof for a replacement head. Just look for replacements with matching casting numbers if that is the failure.

I suspect prior engine heat damage then sold to you.