1986 Merc 350 exhaust overheat

[Liberator1]

I have a 1986 Merc 350 that the engine stays cool but one side of the exhaust overheats. There is more water coming out of one side of the thru-hull exhaust than the other side that gets hot.

I have inspected the tee-valve assembly with the 2 balls and 2 springs but it seems OK.

Anyone know what is inside (if anything) the exhaust elbow ?

 

[HT32BSX115]

Re: 1986 Merc 350 exhaust overheat

Howdy,

A Four Winns Lib?


If you have more water on one side vs the other and your "balls" are OK,


You may have a plugged riser or manifold on the side with low flow....


If you have not removed the risers and checked them for leakage (ever) NOW is a good time to do it!!



Cheers,


Rick

 

[Liberator1]

Re: 1986 Merc 350 exhaust overheat

Hi Rick,

Yup, 261 Lib with twins, double the trouble.

Before that had a 241 Lib with a single 460 King Cobra that I blew up real good....I use that Mobil 1 syn oil from now on !!

The side that over heats has low flow for a minute then gives a big "woosh". This repeats itself while the other side has a constant flow of water.

Do you think it could be water pump pressure or something else?

Had a chuckle with the "balls" comment...

Thanks,
Lloyd

 

[HT32BSX115]

Re: 1986 Merc 350 exhaust overheat

Before that had a 241 Lib with a single 460 King Cobra that I blew up real good....I use that Mobil 1 syn oil from now on !!

Hi Lloyd.....man, I'll bet you're as glad as I am to be rid of that 460!!!

I would absolutely LOVE to have a 261!! My dream setup would be with a pair of aluminum 383's with aluminum manifolds/risers, and Bravo III's on the back!! (My 460 211 Lib was a complete DOG outta the hole before but fast once it got up on a plane.......With the Bravo III now it just ROCKETS outta the hole and is about 3 MPH slower!!) A 261 with aluminum 383's and BIII's would be a ROCKET too!!


I am almost thinking you have a "flow" problem on one side.

It could be raw water pump fragments in the PS cooler, and/or the T-stat housing or a problem with those check balls etc.....

 

[Liberator1]

Re: 1986 Merc 350 exhaust overheat

You bet Rick, that single 460 just couldn't get on plane especially with a boat load full of people and gas...was actually embarrassing ! The 4-barrel just howling and the bow pointed up to the moon ! LOL !

Actually, what got me through a long trip I was on with 6 other boats was to put a "C" clamp on the hose to the "good" exhaust side to force more water through the over heated side exhaust and it worked good so far but need to get to the root problem.

Still need more ideas why this is happening...

Thanks

 

[HT32BSX115]

Re: 1986 Merc 350 exhaust overheat

You bet Rick, that single 460 just couldn't get on plane especially with a boat load full of people and gas...was actually embarrassing ! The 4-barrel just howling and the bow pointed up to the moon ! LOL !

Yeah! I remember how the 460 King Kobra was when my brother had my boat...(he bought it new) ! Even at sea level, If it had more than about 5 people in the boat.....it would point at the sky for quite some time ( trim setting all the way IN) before it would finally plane!!

We took my 211 to Lake Tahoe last Aug and had 9 people and 3 100lb dogs in it and it still planed and still got up about 45 mph!! I had to take the 26p props off and put the 24's on though, but I was amazed that it would plane at all at 6000 ft altitude!! (of course......now I want a tricked out 502!!!)


If your raw pumps are in good condition, I really think that you may have some blockage either in a riser/manifold or a hose feeding them (assuming the t-stat housing-check balls are set up right) ....


If you had a raw-water-pump failure in the past, and you didn't check for pump fragments downstream of them you might look there too....

 

[jerryjerry05]

Re: 1986 Merc 350 exhaust overheat

You running it on the hose or in the water?The hose will NOT deliver enough water to do a good job.In the water:impeller or the manifold/riser is probably clogged.Possibly an exhaust flapper could be stuck in the bottom of the Y pipe.J

 

[Liberator1]

Re: 1986 Merc 350 exhaust overheat

The one side of the exhaust over heated on the water and also runs a lot hotter on the hose. I will try and dig up some cooling system diagrams so I can visualize what you are talking about.

Thanks for replying Jerry

 

[Bondo]

Re: 1986 Merc 350 exhaust overheat

I will try and dig up some cooling system diagrams so I can visualize what you are talking about.

Ayuh,... Pull the riser off, on the Hot side... It's probably Plugged up...
It don't matter how much water you try to push thru it, if it's Plugged, the water can't flow Out...

 

[HT32BSX115]

Re: 1986 Merc 350 exhaust overheat

Possibly an exhaust flapper could be stuck in the bottom of the Y pipe.J

I think he said he has thru-hull exhaust......

 

[Liberator1]

Re: 1986 Merc 350 exhaust overheat