IMO, not likely

If a flapper was stuck that badly, the exhaust - and the water in it - would revert into the engine. You would notice it quickly due to poor running at a minimum and engine damage at the worst.

have you run the boat in salt, if so, check for corrosion and blockages in the exhaust manifold

Well, I was hoping it would be a simple solution. IR temp gun next time out, but will check the oil cooler for junk prior to that and impeller also.

Wasn't stuck all that tight and I don't know if it was free and only stuck when I shut the motor off. It popped loose pretty easily and it looked like there was decent water flow coming out. Boat was running perfect.

No salt as far as I know. Prior owner (2nd owner) boated exclusively at Havasu and New Mexico. Don't have any info about original owner. Will be taking the OEM exhaust off this fall and replacing it anyway with IMCO.

May be a normal situation as previously stated, riser and manifold just seemed warmer than I remembered or expected. Water wasn't all that cold on Friday and temp was in the low 80's.

If all else checks out normal in the cooling lines, and impeller/housing are in good shape, you may want to check the fitting on the interior side of the transom assembly. There's a 90 deg barb fitting/housing on the assembly which holds water and over time will corrode the aluminum on the transom assembly which in turn collapses the intake hose coming in the from the helmet/bell housing where the drive mates up.

Here's what a bad one will look like.

http://i215.photobucket.com/albums/c...s5slttt00.jpeg

With silent choice and one of the flappers gets stuck closed it creates higher exhaust pressure on the closed side so the water goes to the open side instead.
That is why one side is hotter than the other. It only is an issue at higher RPM's.

This plus this

Finally got the chance to put my boat in the water again. Backed the boat down the ramp and ran the motor on the trailer. I realize that this is not the same as actually running the motor and checking, but it's all I could do today.

After motor heated up, there was about a 15* difference between the port side manifold/riser and the starboard side. Starboard manifold was the warmer of the two. I really don't think there is a problem now, but I will keep an eye on it to see. There was no steam today as the temp was almost 90 here. Exhaust tip water looks almost identical.

Will keep an eye on it, and see what happens. Thanks for all the responses.

Sounds like all is good to go. See ya out there

From what I've been told and researched the SB will always be a touch warmer. Looks like you're good for now. With a circa 1996 boat and risers/mani.'s that I don't have a replacement date on, I carry my IR thermometer with me every time out. Will be doing R&M's this summer.

Keith