1998 mercruiser Over heating Exhaust problem

[canal cruiser]

1998 searay 5.7 mercruiser alpha outdrive. Took it out year before last had what appeared to be an engine fire. towed in. $2000 repair bill to replace bellows,impellor and hardware. One trip out went well. Went out last year, cruising slow 20-30mph. two miles out smelled something burning, smoke from engine compartment,shut down got towed in. Found the exhaust connections from starboard riser toasted. Figure I need to replace riser and maybe exhaust manifold? Is there anything else I should be looking for? don't want to keep replacing the wrong parts.Any help would be better than none.Thanks.

 

[Don S]

Re: 1998 mercruiser Over heating Exhaust problem

If it does turn out to be exhaust, you do not just replace one side, you do both. If the risers are plugged up, chances are the manifolds are due for replacement also. Do you boat in salt water or fresh water.

Have you done any testing on the water output from the pump? Does it overheat at low speed or just at higher speeds?
Is this a raw water cooled system or closed cooled?

 

[canal cruiser]

Re: 1998 mercruiser Over heating Exhaust problem

It's raw water cooled. When I bought it about 6 years ago the previous owner said he had one riser replaced. I'm betting it was the port riser. No issues on that side. I run in brackish and salt water but always flush it out after a trip, kept on trailer.The exhaust tube is fried on the starboard side so I know that has to be replaced. How do I check water flow from the pump?disconnect the in line and check for water flow while running on the muffs? Hey, thanks for the reply!

 

[Don S]

Re: 1998 mercruiser Over heating Exhaust problem

This should explain.
NOTE: The boat has to be in the water for this test, not on muffs.

View attachment Output test 24.pdf

 

[canal cruiser]

Re: 1998 mercruiser Over heating Exhaust problem

Don,
Thank You! once I get it back together, I'll drop it in water and give it a try.Thanks Again!