I was running it for only about 10 minutes today - it was running fine and then all of a sudden it started to slow down and within 5 seconds stalled. I first tried to restart it but I noticed it was turning over real slow. So I then looked at the temp gauge and saw it at 180F (the red area is at 220). I opened the hatch and heard alot of crackling and upon touching the top manifolds they were very hot to the touch. I pulled it back to my dock. About 30 minutes later the gauge was at 140 and the crackling stopped and the manifolds were OK. I tried to restart but still the engine is turning over real slow (and didn't start). I did check the oil and it was clear and full.

So a few questions:

1) what should I do next - should I just let it sit for a few more hours and retry?
2) any ideas of why it would have overheated on me - what should I check first? Note that I recently put on a new gimble bearing and last year put in a new water pump impeller. we do have lots of weeds in our lake - could the water inlet holes have gotten plugged?

Thanks

1) Pray and also let usknow what you have exactly for a motor. Serial # helps.
2) Tons of them. And yes, weeds can get in and block flow.

Don't try to start again ubtil you pull all spark plugs and check for water on them. You could have hurt a headgasket/warped an exhaust manifold or riser/ and put water into the engine...this will make engine hard to crank. Water in combustion chamber can bend a connecting rod when engine is turning because water doesn't compress.

Let us know from there and will go further if need be,

Sorry to hear, weeds or even a plastic grocery bag getting around the intake can make it over heat fast.

its a 92 merc 454 330HP (not a mag) with bravo1.

I just checked the outdrive water inlet ports - they looked fine and not plugged with weeds. I then tested the 2 batteries to perhaps see if they were the cause of slow turning over and both were 100%. So I tried once more to start (being the engine is now cool) and same thing - it turns over but real slow (like one rotation every second) and the longer I keep the ignition on the slower it gets (obviously it does not start).

I'll bring it to shore this weekend and check the plugs as suggested. Though based on the symptoms (turning over real slow after overheating), what is the most likely cause?

BTW - I replaced the head gasket 2 years ago, and put new heads on (I had the peanut heads and now go 737 or 7 something - I can't remember but they were supposed to be the better heads for my motor).

My opinion your motor is seizing up, and total overhaul or replacement is needed

I think I'm ****ed - I just removed all the plugs and no sign of water (which is good). But then I tried to turn it over (with all plugs out) and it still had a hard time turning over) - my experience is with all plugs out there is minimal compression so the engine should turn much easier. Anyway I got out my compression tester and tested only the 4 holes on the left side of the motor (facing back) - all had basically no PSI except the third one which had 100 - but to be fair the engine was turning over so slow that I'm not sure if the compression test was accurate. But as I was testing those 4 holes, each time I tested the engine did turn slower and slower. And on the last one, it basically stopped turning (like it is seized).

So need advice - what should I do first to diagnose this? Should I remove the intake - will that show me anything? Or should I remove the heads - will that show me anything? Not sure what I should do next - other than lite this POS on fire

Just for grins, I would check the drive to make sure its not seizing up. Pull the drain plug from the top of the drive and make sure the oil isn't burnt. Then I would pull the drive off and see how the motor cranks. I realize its not very likely, but I would give it a look before tearing the engine apart. If the engine has to come out, you will be pulling the drive anyway

Did you try turning it over by hand with a breaker bar to see how hard it is to spin?