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Discussion Starter · #1 ·
2002 40 hp 4stroke overheats at wot. Already did the water pump. May check thermostat before I take it in. Anyone have a recommendation on who to go to?
 

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Mike @ Governors Creek marina
Jeff Reedy @ Ilse of Palms Doctor lake
Donnie @ Ilse of Palms Palm Cove Marina
Charlie @ River Maine

All very good merc techs, and good guys. Good Luck!!!
 

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Im not merc but $50 says its your thermostat
Depends if the motor is pumping good water, if it is then I would suspect a lean fuel condition. That motor I do believe is a carb model; and if so those carbs can be a pain.

All the names listed in Tarpon's post I 2nd  [smiley=1-thumbsup2.gif]
 

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Well, he said he had/did the waterpump. So "assuming" its pumping good water, a thermostat thats stuck closed won't cause an overheat at wot?? Really??. :-? I would take a wild guess and say if te carbs were gummed up and it had a lean issue that he wouldnt be getting wot. ::)
 

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Well, he said he had/did the waterpump. So "assuming" its pumping good water, a thermostat thats stuck closed won't cause an overheat at wot?? Really??. :-?     I would take a wild guess and say if te carbs were gummed up and it had a lean issue that he wouldnt be getting wot. ::)
Maybe I should have been a little more detailed in my previous post. Absolutely a stuck thermostat will cause and over heat problem, however with my experience with these engines it would be throughout the mid-high rpm range not just WOT.  If only 1 carb  typically the bottom carb has a small restriction then yes you could still be getting close to WOT not noticeable but on a tach and cause the motor to warm up just enough to activate the overheat sensor. By all means I would check the thermostat, as that would be the 1st place a dealer checks; was just giving my .02 ( which isn’t worth much) from when I was a tech and my experience with the carb 4stroke motors. My dealer sold a ton of program motors from merc/Canada and this was a very common issue as to the point all motor sold would automatically get a carb job.
 

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Creekrunner, no big deal. Sorry i kinda jumped on you. Sometimes i see people give other people bad advice (not that yours was irrational, just didnt sound right from the first post) and bad advice is worse than no advice. No biggie, just two different debating minds. Btw, i thought more about it and a thermostat that is stuck open will actually cause an overheat too. So anyone reading this, NEVER TAKE OUT YOUR THERMOSTAT! It will not run cooler.
 

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You are right about a stuck open thermostat, the only motors that would run with out them were the older OMC 70,80,90's models. When we use to run 2.4-2.5 Mercs on the drags boats we would run 1/4 SS washer in place of thermo's to restrict flow a little.
 

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Discussion Starter · #10 ·
Thanks for all the replys fellas & sorry I led you down the wrong track. The motor is an EFI model 3 cyl. Did the waterpump - pushing water fine. Think its the thermostat as well...its being investigated as we speak. I say it only does it at WOT, but I didn't run higher end RPMs but less than WOT for long. Did fine at mid RPM for ~ 10 min or so. Letting the experts handle this one.
 
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