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2020 Mercury V8 flush port MORE problems....

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2020 Mercury V8 flush port MORE problems....

Old 06-10-2021, 01:01 PM
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Default 2020 Mercury V8 flush port MORE problems....

Last August, I bought a brand new SeaVee 290b (love it, see my build thread) and made the decisions to put two of the new Mercury V8 300's on it, instead of the the older inline 6 350's. In general, I like these engines. But I've had some major issues with the flush valve system. Most annoyingly, the flush valve caps are near IMPOSSIBLE to remove (the hose inside the engine attached to the valve and the plastic tie down that holds it in place and the o-ring gasket make for such a tight fitting, that it impedes the removal and attachment of the valve cap). See this thread for photos, other people's similar problems, and some of the clever hacks folks have used to deal with this problem. Personally, I end up having to pop the engine cowlings off in order to push the hose from inside the engine outwards to pop open the flush valve. Crazy.

But I now have a bigger problem, which is more than an annoyance: on one of the engines, when it's running, it's spewing water out of the overflow holes in the flush valve (see attached video). The engine is also now running 5-10 degrees hotter than the other engine. I've talked to both SeaVee and Merc (and my local marina, which is a long-time Merc service shop) and they are not concerned that running the boat in this conditions will create a problem, but clearly it's not something that I can leave unaddressed. SeaVee recommended I try running the engine in throttle only mode with the hose running throught he flush system to clear it out, but that didn't work. The marina thinks it requires replacing a check valve.

Curious if others have run into this issue on the Merc V8's - or any other outboards for that matter - and what the solution was in these cases.

Very frustrating.
Old 06-10-2021, 01:09 PM
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Im not sure it’s the same issue but if the water is leaking through the cap on the flush port a cheap and quick fix is to put a nickel (5 cents) under the cap and screw it on the flush port.
Old 06-10-2021, 01:13 PM
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I have one of the old V6 300 Verados and would do the same thing, just debris caught in a check valve. No issue running it like that - aside from a little brain damage worrying about it - and replacing the valve fixed it. I also have a pair of the new V6 225's and had that same issue with pulling the flush ports out of the cowl. I had to get pliers involved to pull them out. When I sent the boat back to the dealer for punch list stuff that was on it and they were fixed. No idea what they did but I know it can be improved.
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Old 06-10-2021, 01:25 PM
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Mine also spew. I just installed a built in flush port and valve set up to flush the engines without having to use those PIA flush ports on the side. And they are a royal pain in the a$$. Exactly as you describe it, each one of those items happened to me. V8 300's.
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Old 06-10-2021, 02:00 PM
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I just repowered with these motors. I noticed it was hard getting the screw off and decided to relocate the flush onto the boat. I just put a barb in and deleted the motor mounted flusher.
I have 11 hours on the motors so far I love them. So quiet and powerful.


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Old 06-10-2021, 03:06 PM
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On my 34 cv I had 300 mercs, went thru a total of 7 check valves, they accumulate debris and than the water shoots out the little holes on the cap, looks like a jet ski, I stopped using those for flushing and now use a muff on my 350's and let the engine run properly. Stop using those check valves/ flush ports.
Old 06-10-2021, 03:13 PM
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Originally Posted by Schmaltz~Herring View Post
On my 34 cv I had 300 mercs, went thru a total of 7 check valves, they accumulate debris and than the water shoots out the little holes on the cap, looks like a jet ski, I stopped using those for flushing and now use a muff on my 350's and let the engine run properly. Stop using those check valves/ flush ports.

So are you putting the muffs on with the boat in the water? If so, I guess you’re able to attach the muffs by reaching out over the cowling? Seems like a tough maneuver but maybe I’m overthinking it?
Old 06-10-2021, 06:59 PM
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Put a quarter in the cap and snug it down, stops the leak.
Old 06-10-2021, 07:46 PM
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These engines sound awesome and troublesome at the same time. Everyone loves them, but so many threads with various issues. Hope all works out OP.
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Old 06-11-2021, 03:36 AM
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Put a quarter behind the cap and be done with it. The V8s use the same flushing check valve assembly as the 6 cylinder Verados. The small spring typically breaks from the shock of cold water coming from your water hose.

Originally Posted by mattttt25 View Post
These engines sound awesome and troublesome at the same time. Everyone loves them, but so many threads with various issues. Hope all works out OP.
People take to the internet to rant and complain about any and every product they own. Rarely do they do the opposite and rave about them. We have sold/installed or service/maintain more Mercury V8s than most people will ever see in their lifetime. We’re pproaching 500. How many threads have you seen me start complaining about problems?
Old 06-11-2021, 04:00 AM
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Originally Posted by mattttt25 View Post
These engines sound awesome and troublesome at the same time. Everyone loves them, but so many threads with various issues. Hope all works out OP.
Very few issues at all it is one of the best platforms out there
i had much worse problems with my Yamaha
Old 06-11-2021, 05:27 AM
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Originally Posted by davidwademarine View Post
People take to the internet to rant and complain about any and every product they own. Rarely do they do the opposite and rave about them. We have sold/installed or service/maintain more Mercury V8s than most people will ever see in their lifetime. We’re pproaching 500. How many threads have you seen me start complaining about problems?
I completely agree with the bolded portion. As for the rest....c'mon man.....you are a Mercury dealer.
Old 06-11-2021, 05:43 AM
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Originally Posted by 6104696 View Post
I completely agree with the bolded portion. As for the rest....c'mon man.....you are a Mercury dealer.
DavidWade posts are spot on, and I think he is honest. Heck, last week he recommended under the correct scenario to not to buy the extended warranty and pocket the money…..and he sells the extended warranty cheaper than most others. What dealer ever says that?
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