stern flush WHOOPS

212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
learned a lesson... could have been a lot more expensive than it was..

my lil 212 has a 357 merc reman with about, oh, less than an hour run time on it.  i converted it to full closed loop cooling before planting it in the boat.  the engine has elbows atop the manifolds and doesn't have risers otherwise- perfect alignment to the Y pipe with boots that came with the engine. 


got it fired up a week or so ago and running it on the trailer realized the foot isn't providing the water needed to push through the heat exchange... so... i hooked a hose to the stern flush fitting and effectively doubled my cooling water coming through... it's not that it overheated, it's that i didn't like the 170* temp it was reaching at idle..... 

this worked... several times... it no longer worked when i killed the engine and was distracted for an hour or so, all while the stern flush hose was running... i returned to the drive to find lakes on either side where grass used to be high and dry....

no worries, right? killed it, looped the hose back where it's home is... go on about my business...

after finally tracking down an electrical issue at the helm, i want to warm the engine before rolling to the launch.  it will hardly turn over... i think it to be batteries- fine... i got something for that in an 120A charger.... an hour later i go to start and same thing... my heart sinks as i move back and pull the dipstick......................... there is at least two inches of water in the crank case.....

pull plugs- spit water everywhere... squirt some WD40 in there, drain the oil swap filter, fill- compression test- 7 cylinders at 205, one at 197, one at 200... not bad- the rings haven't even seated yet... plugs back in- fire her up... nice.. run to temperature (no stern flush) drain oil swap filter.... x5.... now? clean oil pan, no trace in filter or upon drain... all seems well... 

here is what happened (and i was worried it would be worse; TG is wasn't)... the stern flush running without engine running comes in same line as foot passage- through the steering cooler to the exchange and out the elbows... without benefit of exhaust pressure it wasn't spit evenly (somewhat) from around the outer ring, but pushed through bottom of the elbow's outer ring... it likely pooled and mostly exited the boat via exhaust, but some didn't... it likely pooled on a casting on the exhaust bellow to Y, and backed up... and directly into the exhaust and waiting for an exhaust valve to open (the ones that weren't already open).  

It's a good idea NOT to run that stern flush unless you're running, especially if you have closed loop cooling.  there isn't enough resistance to drop it's pressure... a LOT of water 'pours' out instead of being forced out.  it WILL backfill through the exhaust in the elbow. 

other things it could have been? a bad seal between the elbow and manifold... it wasn't- but that was the 2nd best option... a cracked head or bad seal on the intake manifold... either would have cost a benji or so after machine shop re-decks and upper gasket kit.... it WOULD have been that, too, if i had't caught it.  

this is simply a public service announcement to, perhaps, don't trust that flush point when the engine isn't running.  i don't even know why it's there if you're pulling through the foot (alpha 1 gen 2) as you shouldn't ever run the engine dry or when the foot isn't submerged- it'll kill that pump in a heartbeat. 


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