O.K. here is what happened. I was towing my son on the tube, he fell off, I turned to pick him up and my audible warning came on. I was at 225 degrees. OK so i shut it down let it cool tryied to put back to the dock. Within 30 sec. I was back to 225 with the alarm sounding off again. I then shut it down and got a tow back to the dock. Upon further investigation I found that my idler pulley spun off(bearings came apart). OK i'm thinkin easy fix. New pullys and restring the belt.By the way i'm 300 miles from home on my family vaca. So Napa orders me the pullys, I pick them up the next day, install and restring the serpentine belt.Ready for action. Not!! now my boat won't start. Has this happened to anyone? Do you think the ECM could be shutting me down ? I don't think I caused any engine damage or did I? it was running when I turned it off.I am really bummed. Please someone tell me something good, like it is just a sensor or something. I have a guy with the software coming today to get a code from the ECM. Yes it does turn over, just won't start, like its flooded or something. Its a 350 mpi mercruiser.It is supposed to be in the 90's this week and I can't stand to see my ride broken.Any info anyone has would be helpful. My wife says I should feel lucky I even have a boat to breakdown. Sure hope this isn't gonna cost me a grip.

Pull the plugs and give them a good look. Crank over the motor and see if any water comes out of the plug holes. 225 isn't over the top hot, its not great, but it shouldn't crack anything.

I cracked a block. I will keep my fingers crossed for you that you NEVER have to go through what I did. Details here: <BR> <BR><a href="http://www.wakeworld.com/MB/Discus/messages/559019/579914.html?1212425931" target="_blank">http://www.wakeworld.com/MB/Discus/messages/559019/579914.html?1212425931</a> <BR> <BR>The folks in the know told me that if the raw water intake is somehow starved, you can get false readings on the temp guage...225 if it's just air in the water jacket is possibly engine destroying temps. <BR> <BR>One thing I did learn from that was to NOT try and crank the engine over if the plugs are still in. The experts tell me that the starter motor has enough torque to bend a rod if there is water in the cylinders. So if you are going to do what Blair suggest, pull ALL the plugs. <BR> <BR>I've got my fingers crossed for it being something simple!

Looks like wet plugs and chocolate milk.bummer! Could it be just head gaskets? A local merc mechanic told me he could do the head gaskets.how can you tell if it's the block?

I am NOT an expert here, but I seem to remember the folks who ARE experts telling me that: headgaskets do not fail unless the mating surfaces are stress disturbed. I believe that heads are the most likely culprit they warp or crack changing surface contact pressures on the gasket. I have machine shop clients that resurface heads all the time. I didn't check on the boating forum, but maybe those folks can BETTER address your problem, if you haven't already done so.

I have a extended warranty, I wonder if something like this is covered? I hope so. This is not good news, if I'm gonna need a new motor.