99 4.3L Mercruiser HOT Riser

To make a long story short i have a 99 islander with a 4.3 mercruiser. Unfortunantly i have been blessed with the single piece exhaust manifold/riser. The boat has never seen salt water in its life. The pump in the outdrive is good. The thermostat is working. One riser is cold (port) and i burt my hand on the other (starbord). I took the hot manifold off and had it smoke tested. The (auto) mechanic said he plugged the three exhaust ports and the center on the outlet. I was not there to witness, but was told smoke came out the water drain plug. Would a cracked riser cause enough pressure to stop the flow of water through that side? I am willing to buy the 2 piece conversion, but would like to see if anyone else has encountered the same issue.

Any advice/help much appreciated

Maybe the flapper fell down and is blocking that side.

Fresh water only risers can last forever.

Maybe it can be saved, remove and cleaned, maybe not.

Smoke came from the fresh water side while he was pumping it through the exhaust side? If he did the test correctly, the results you are posting indicate that the manifold/riser is no good. Nothing lasts forever.

These are now nearing 14 years of service, so it may well be worth replacing them, rather than replacing an engine due to a manifold failure.
Much less expensive also.

With the two pc manifold/elbow system, you'll have the ability to routinely pull the elbows and inspect the sea water transfer ports.


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RicardoMarine said:

These are now nearing 14 years of service, so it may well be worth replacing them, rather than replacing an engine due to a manifold failure.
Much less expensive also.

With the two pc manifold/elbow system, you'll have the ability to routinely pull the elbows and inspect the sea water transfer ports.


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Ayuh,.... Considerin' the Problems they had with core shiftin' in the castin' of those things, they were Junk 14 years ago...

I've never seen a set I could trust, 'n have seen dozens that destroyed the motors they were bolted too....

bondo said:

Ayuh,.... Considerin' the Problems they had with core shiftin' in the castin' of those things, they were Junk 14 years ago...

I've never seen a set I could trust, 'n have seen dozens that destroyed the motors they were bolted too....

Click to expand...

It just so happens that I am a tooling engineer at a foundry so I know exactly what your saying. I appreciate all the feedback. I will be ordering the complete 2 piece system for both sides. 800 is much cheaper than a new engine. I will let everyone know if it solves the problem. Thanks to all

Stay away from GLM and Sierra (same). Stick w/Barr, Osco or the expensive Merc. model...they also make a cheap one.