Maxum 1997 2300SR 5.7 V8 Overheats at 4k rpm
I have got a strange issue on my hands. I bought a 1997 2300SR and took it out a couple of times. It ran fine (so I thought).
Took it into service and they told me that the distributor was on 180 degrees off which makes timing really really hard. So they corrected that issue and timed and did a tune up on the boat.
Took it out on the water and noticed a very big increase in RPM and speed. 3200 to 4200 increase. After 20 minutes on the water and about 4 minutes into WOT, i hear a pop and the engine slows down and kills. Start it back up and clank, clank, clank. Get towed in.
Open up the engine and find that #6 piston has a chunk missing. Fine. Rebuild engine.
Engine is done, runs like a dream on the trailer, so smooth! My mechanic is AWESOME! I take it out on the water, and at 4k after 15 seconds, we hear pinging due to overheating. Exhaust manifold is hot, risers are cool. We figure rust is too bad so we replace both risers and 1 4" spacer. Other was fine.
Take it back out, same issue, but the risers are now getting hot. Something is not letting the engine cool. Flow from impeller is good, replaced the water pump, thermostat is new (i was told to get a 160 degree one). If I hook a garden hose to the input to the exhaust manifold, water flows like Niagara falls. So no blockage there.
So I have a boat mechanic take a look and he thinks about a old service notice to move the thermostat to the lower position in the housing. We then decide to go test this.
Out on the water, same thing, engine overheats. We remove the thermostat. Engine sits at 125 degrees on the gauge and runs great. Risers, elbows stay warm (not hot, not cold). Told this is perfect even at WOT.
So we inspected the thermostat housing a little further and noticed that the water coming in to it was touching the thermostat and not letting it open. We think that there might be a breach in it?
So my question is this. Was there a modification that I don't know about to solve this issue? Running at WOT should not overheat the engine right??