www.iFourWinns.com

Ok, at the lake last time out and shifting went out. At this time, there was a rather large puff of smoke come out of the exhaust as the engine revved up due to the loss of shifting. We have replaced the transom, getting ready to put all back together. One of the exhaust flappers is melted, have already bought a new one and replaced. I know this is typically due to overheating, but the boat never has been above 160. My question is, can that flapper melt by any other cause besides overheating? Could it melted quickly due to the high rpms experienced when the shifter went out? And is this likely what the black smoke was from? Coupler, impeller, drive and ujoints all are good.

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1990 Horizon 200
5.7L OMC Cobra 260HP

I don't know about the OMC's but Volvo sent a service bulletin to remove the exhaust flapper and not replace them.

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Terry
Current: 07 Crownline 255 CCR cuddy - 350 Mag MPI/B3 "Casi Cielo"

Previous:97 245 Sundowner 5.7GI/SX

Tow vehicle: 1986 GMC 2500 Camper Special 454/TH400

For sure those OMCs had flappers and I would not remove them, it is possible for the engine to not overheat but the exhaust can....I have not ever experienced it but I have heard of it happening, in fact I recall reading that some late model Volvos were coming with exhaust temp sensors to warn you of this...smoke could be the rubber exhaust hose melting... if the coupler failed....you would have had both overheating and no drive...when you pulled the engine did you see a bunch of rubber particles around the rear of the engine? If so the coupler could be it...I'd probably change it anyway if you have it all apart...also look at the engine oil pan when you have the engine out for rust spots...

the only way for a flapper to melt is if the exhaust system does not get enough cooling water...if your exhaust risers were clogging up, then that could happen even if the impeller is good...the boat's over 20 years old, are the manifolds and risers original?

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II