Exhaust riser is very hot on one side of the motor.

[suss1173]

I replaced the exhaust manifolds, extensions,and elbows toward the end of last season. However, I did not get to use theboat much after doing the work. I notice the elbow on one side is very hot.When I put my hand on the outer elbow (top part) it is very hot where all ofthe others are just warm. I’m guessing I put the gaskets in the wrong spot.

After I took apart the side that was getting hot and realized I had therestricted gasket with 2 open slots on the bottom and top of the 6' extensionblock. I left a restricted gasket (2 open slots fore and aft) on the top of theextension block and replaced the lower gasket that sits between the extensionblock and the manifold with a gasket that’s open all four sides. Unfortunately that did not fix the issue, theone elbow is still getting hot while the other side is cool.

I don’t know if this is a related issue,but I also notice the motor starts to overheat if I let it idle. If I increasethe RPM's to about 1k RPM or more, the temp comes down to the normal 145 rangeregardless if at the dock or underway. FWIW- the water pumps were replaced lastseason.

Any help would be appreciated

 

[julietbravomike]

You need to find a service manual and make sure you have the gaskets in the right places and everything plumbed correctly. But, why is the cooling water for the elbows plumbed into the extension and not directly into the elbows? Is that how they were plumbed before? If the restricted gasket is supposed to be at the elbow/extension joint, then it's going to restrict the amount of water that flows through the elbows, yes? My boat isn't set up like this, so take my advice for what it cost you.

 

[suss1173]

^^^ thanks for the suggestion but the way it sits in the picture is how it was plumbed b/f and the other motor is plumbed the same way and both sides of that motor are running cool (at ideal and at speed).

I belive the the gaslets are in the proper place now with the restricted one (two open slots bow /stern) on the top of the extension and the open one (four openings) on the bottom of the riser.

 

[El Capitan]

Port side is obviously leaking...see dripping rust stains

 

[suss1173]

Port side is obviously leaking...see dripping rust stains

It was leaking,but that was corrected and currently the gaskets on the top and bottom of the extensionare new. However the riser is still getting very hot.

I know there are balls that look like a pressure relief valve coming off theT-stat housing. I don’t know how they work, but notice they are on that linethat feeds the riser. Maybe they are getting hung up on the one side? I'm goingto explore that today. If anyone else has suggestions, please do share.

 

[Strecker25]

I dealt with a hot condition on the stbd side of both of my 350 EFI's and found out i was chasing a ghost, as it was how merc designed our motors for that year (1998's) Once the Tstat opens the preheated block water empties out that side. stbd mani/elbows run at 130-140 and ports run around 110-120

That being said, if the motor is overheating at idle you definitely have some issues. First thing is to get the right gaskets in all locations. I used this merc bulletin to determine that we needed all open slot gaskets.

https://drive.google.com/file/d/0B8tkSPwvgBWOMUoybVZOMHVUM0k/view

I also question why the bypass water is going to the riser and not the elbows, but I'm no professional so that might be worth a call to merc. Either way, I interpret your setup as 4b which would mean you need a a full flow between the manifold and riser and a restrictor gasket between riser and elbow.

What year are the motors, and do you have the S/N's?