496 HO Overheating!!

[Southwest47]

Well, I took my boat out to the lake today for my last trip before winter storage. About 10 feet off the dock, the audible warning signal came on. My oil pressure was okay, but my engine temperature was at 180 after only about five minutes!!
I think it is a faulty thermostat. Im thinking of changing it myself. I have knowledge of auto engines, but I am inexperienced with marine engines. Has anyone changed a thermostat? Is it a difficult repair? Any thoughts, suggestions, how-to tips, would be appreciated.

[shadow]

Well, I took my boat out to the lake today for my last trip before winter storage. About 10 feet off the dock, the audible warning signal came on. My oil pressure was okay, but my engine temperature was at 180 after only about five minutes!!
I think it is a faulty thermostat. Im thinking of changing it myself. I have knowledge of auto engines, but I am inexperienced with marine engines. Has anyone changed a thermostat? Is it a difficult repair? Any thoughts, suggestions, how-to tips, would be appreciated.
I wouldn't just "guess" and replace the thermostat.I would suspect the impeller before the t-stat.Easy way to verify "if" it is the impeller.
Remove the water inlet hose to the heat exchanger(right side) facing the engine.Fire the boat up either in water or with water on to the ear muffs,Cover the low water pick up if equiped and there should be water flowing out the hose that you removed from the heat exchanger.If not
the impeller is the suspect,make sure to get all the impeller chunks out when replacing the impeller.

[daytona22]

it can also be a clogged heat exchanger OR a clogged oil cooler. depending on where u boat, in water intakes suck up small pieces of crap that is to big to get thru the holes of the cooling lines in the exchangers, limiting the flow, limiting the cooling, causing the alarm to go. does this sound like experience talking? because it is. we did the impeller, even though it looked fine. still wouldn't run. after many hours of searching, we found the problem by calling Alton Blakley marine and talking to Vern in service. they sell hundreds of 496's/year and he knew what the problem was b4 i got done explaining what the motor was doing. u can take the end caps off the exchanger and look inside to see if this is what the problem is, and the gaskets r only $4.00 apiece. nothing drains out of there except lake water. the oil cooler can be removed, cleaned, and replaced w/o any new parts. merc has a billiten out on the problem, but won't do anything to help cover any expense, even though they know that u either need a really good strainer in front of everything, or u need to perform the service regularly to avoid troubles. yhe exchanger can be cleaned with a small piece of coat hanger. u need to determine if u have the 33/4" or 4" exchanger to make sure u get the right gasket. merc originally went bigger on the cooler to try and fix, but it doesn't work either. i wouldn't mess around w/496's unless u have the diagnostic tool hooked up - there r tooo many sensors to try and guess your way thru. if u take the boat somewhere, make sure they have the tool and have worked on THIS motor b4, or u r going to be wasting alot of time and money hunting.