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 How often to replace exhaust manifolds
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775 Posts

Posted - Jul 03 2020 :  15:17:19  Show Profile  Reply with Quote
I got hydrolocked! My motor was replaced 2016 I thought I had a minimum of 5 years, but no. Also if you use your boat often or rarely which is better for riser longevity? I got a $4200 bill for this, sound right?


2600 Posts

Posted - Jul 04 2020 :  09:23:50  Show Profile  Reply with Quote
You don't say what that $4200 covers. I changed mine at about 15 years and they still appeared to be in good condition. But at 15 years, they didn't owe me anything. I suggest their lifespan can be increased if you flush each after saltwater use.
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9337 Posts

Posted - Jul 04 2020 :  18:00:05  Show Profile  Reply with Quote
In SW use, common recommendation for preventative maintenance replacement of ex. manifolds and riser/elbows on RWC engines is every 3-5 yrs. Much longer but not forever in FW.
Of course on full FWC boats ex. manifolds usually tend to last the life of the engine, so just the riser/elbows are replaced. A lot of people prefer to wait until something happens and pay the price. If one chooses to do that it would be wise to at least check the parts passages on the normal schedule and if you get that far I figure you might as well go ahead and replace to start the clock at 0 again. .
I had 1 riser/elbow start to fail after 2 yrs but that was a very uncommon experience. Usually they are starting to clog after 4 yrs and the tops of the elbow may have been getting a little too warm to keep my palm on indefinitely at any rpm.

FWIW- On my full FWC T/I/B engines I replace the elbows on one engine , then the next engine's 2 yrs later and so on to make the process take 1/2 the time the years I do this. And I always deck the elbow mating surface flat with a sharp mill bastard after 1st covering the surface with ink marker.
That surface is never flat when we purchase these exhaust parts and the 1st few strokes of the file clearly demonstrate that.
Fasteners also get re-torqued to spec after the 1st few heat cycles then annually at the beginning of my (usually) 6 month boating season. I suspect not doing that could contribute to internal leakage at water passage gasketed joints in some cases.

Stephen's point about flushing is certainly very good but my engines have never been set up for flushing and that flushing would be a complex difficult process usually after dark on my boat at a slip where I need to be quiet and gone as quickly as possible after the boat rinse.

But deteriorated exhaust parts are not always the cause of a hydrolock. Could you have been at cruising speed and had the engine ignition fail to stop the engine suddenly, or might you or someone have chopped the throttle to stop too quickly, or was timing way off, or could it be an 8.1L engine with its valve overlap issue that drowned so many of those engines ?

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