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Manifold swap-out

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vandyman

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I recently had intermittent alarms sound (constant above 2800 RPM) and have checked all fluids, temp (~170 at guage), volts good, etc... and all is normal, engine seems to start and run just fine, oil looks new, no bad smells or obvious issues. It is a 2000 Merc 5.7 TKS with an Alpha 1, captains choice, and manifolds/risers replaced in 2007 but run in salt water for 2-3 years prior to my ownership. Today after a warm up it alarmed at about 2800 RPM. I checked the riser temps and the port riser is 170 degrees, stbd is 110 degrees right after coming to a stop. Alarm goes quiet below 2600-2800 RPM. I'm thinking the shift sensor may need to be checked, but also plan to see if their is an obstruction in the Y-pipe as this seems to be a large temp differential (the alarm may or not be tied with the heat issue so I am addressing both).

Question: If I need to replace manifolds/risers, can this be done without removing the engine? My SELOC manual does not go into much detail but I have a fair anount of engine bay room in which to work and think it is feasible (my boat is on a lift). I also plan to replace power steering cooler and thermostat housing if I replace the manifolds/risers. More general maintenance planned for after the season but this can't wait. Thanks in advance... hope all here are having a great season so far (hot here in TN).
 
When was the impeller changed last in the drive ?

More then 2 years you need to change it and the shaft bushing.

Say you do that and the alarm goes off again, the t-stat is next.

Next it will be time for the risers, more then 5 years it's time.

Mani's maybe not.

And yes there are flappers in the pipes right after the risers they may have fallen off and need to be fished out.

Replacing them is up to you. Or maybe not replacing them.
 
risers and exhaust stuff can be changed in the boat,easy enough to check the flappers, stuck or broken flappers cause funny things. The impeller like Chief said could be a problem, especially if a piece broke off and is affecting the T-state, out drive bottom needs pulled on an alpha one for that.
 
Thanks.... you have validated my plans. The impeller was replaced last year but I will do a major service either this fall or in the spring... 1st step is to check the risers and t-stat (and that alarm). Thanks again......
 
I do, and that is the first thing I checked. Topped it off to the fill line to be sure and ran at low RPMs for a while, but alarm still sounds when I hit ~2800 RPM. I will check the sensor and the interrupter sensor this weekend along with the condition of the risers.
 
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