Fresh water flush kit

Sea Señor

Member
Aug 31, 2021
55
South shore, Long Island NY
Boat Info
2010 280 Sundancer
Engines
Mercruiser 350 MAG MPI w/bravo 3 drive
Greetings fellow boaters, I just recently replaced my manifolds and risers in my 2010 280 sundancer. I have a single 350 MAG with cats. Someone recommended I install a fresh water flush kit to extend the life of the manifolds and risers. Does that really make that much of a difference? Spoke to mechanic at the marina and he said no. Easy job but doesn’t really help. He also said to replace man and risers every 5 yrs. Seems a little early to replace. Any thoughts? Thanks
 
I have a twin engine 2010 boat and just did manifolds and risers so I feel your pain. Freaking parts are expensive and to make matters worse they're very difficult to find! I have to agree with your mechanic. The real wear and tear is heat cycles anyway. We run them and when they cool the metal rusts and flakes a little every time also we have winter. Did you ever run your boat before putting in the water after the winter layup? Nothing but rust colored water for at least a few minutes.
 
Greetings fellow boaters, I just recently replaced my manifolds and risers in my 2010 280 sundancer. I have a single 350 MAG with cats. Someone recommended I install a fresh water flush kit to extend the life of the manifolds and risers. Does that really make that much of a difference? Spoke to mechanic at the marina and he said no. Easy job but doesn’t really help. He also said to replace man and risers every 5 yrs. Seems a little early to replace. Any thoughts? Thanks

Let's think about it this way.
  • We know that salt water is highly corrosive, more so than fresh water. Note how much longer parts last in fresh water locations.
  • Salt water tends to have more "critters" and minerals.
  • Yes, engines will take in the saltwater during operation.
  • But for most of us, engines spend most of their time sitting at the dock or on a trailer.
  • If you don't flush your engines they will be sitting there full of salt water, marine life, and minerals corroding things.
  • By flushing with fresh water, you are setting up the engine to sit idle with the least amount of highly corrosive salt water sitting in it.
Is a fresh water flush the be-all, end all that solves all engine ills? Eh, probably not. But it's also the best chance you have to help reduce corrosion and blockages from salt water and marine life - the critters can't live the fresh water so they won't grow in inside of a fresh-water flushed engine. The next level would be to also use a salt remover like Salt Away during your engine flush. The time commitment and effort is not great; it takes me total of 12-14 minutes to flush my engine and generator after an outing, including getting out and putting away the hose.

Here's some info on flushing, and the merits from Tony Athens, a Cummins engine specialist, owner of Seaboard Marine, and general diesel engine guru. He coined the term "marine age" to describe the effects of salt water sitting in marine engines when they are inactive.

https://www.sbmar.com/featured-article/marine-age-the-real-age-of-a-marine-diesel-engine/
https://www.sbmar.com/articles/the-benefits-of-fresh-water-flushing-your-marine-diesel-engine/
 
My personal experience says replace every 5 years

Incident 1:
I brought my 280 to Marine Max Quincy to trade up to a 350. When Marine max went to start it the next day to test it, it hydro locked, water in the engine from a busted manifold. They took 10k right off the trade to fix the engine. The manifolds were 8 years old.....

Incident 2:
The new 350 I owned started overheating when I throttled down. It was 7 years old. So I decided to bite the bullet and replace the manifold and risers myself. The lower drain on the manifolds were completely clogged with rust flakes. Parts were pricey but the boat immediately ran great!

Flushing may slow down the rust problem. But are you really going to flush the salt out every time you use the boat???
 
What @b_arrington said. If you are diligent and do it every time, and more importantly YOU think it's worthwhile, do it. And if you plan to keep the boat for another 5 years. Good selling point for resale as well, shows me as a prospective buyer you took care of your boat, even though I have no idea if you ever actually flushed it.

Previous boater bud of mine used to flush both of his engines after every use AND add salt cleansing/neutralizing stuff. Took him about an hour to flush.

Reminds me when I was looking for the last boat of all of the Neuta Salt Volvo Penta systems I saw where the tanks were empty. Brokers loved to point it out, and then I'd say "But both are empty?". "So when was the last time you used it?"
 
My personal experience says replace every 5 years
Flushing may slow down the rust problem. But are you really going to flush the salt out every time you use the boat???

Yes, I do for both my main engine and generator. It doesn't take long, and I can usually do it while performing other closing-up stuff.

I am, however, running a different type of engine so my incentives may be different. I have a big aftercooler, marine gear/fuel cooler, and heat exchanger to protect.
  • An aftercooler is $4100.
  • An aftercooler core is $2000-$2400.
  • A heat exchanger is $4100.
  • A gear/fuel cooler is $1100.
So I'm protecting upwards of $9300 in parts alone. I'd say investing ~15 minutes of time to fresh water flush is time well spent.
 
Ferrous metal is difficult to protect, once salt is introduced electrolysis begins, rinse all you want rust wont stop
 
Greetings fellow boaters, I just recently replaced my manifolds and risers in my 2010 280 sundancer. I have a single 350 MAG with cats. Someone recommended I install a fresh water flush kit to extend the life of the manifolds and risers. Does that really make that much of a difference? Spoke to mechanic at the marina and he said no. Easy job but doesn’t really help. He also said to replace man and risers every 5 yrs. Seems a little early to replace. Any thoughts? Thanks
 
In saltwater, manifolds and risers should be replaced at least every 5 years. I have the perko flush kits on both engines. Flush with salt away after every run.

Especially important with the cat manifolds. Lots of small cooling passages to plug up and the cats get up to around 2000 degrees at full tilt.
 
I think the approach to flushing is tempered with how often you use the boat, how easy your flushing system is setup, and how closely you follow directions. @b_arrington is spot on with the merits of flushing. But you need to know that there are risks as well.

When I first bought the 340, I was happy that a Perko flushing kit had already been installed on it and the previous owner was emphatic that they flushed after every outing. I learned later that the reason for this was that the guy worked on an Alaskan crabbing boat, so he was away from the boat for long stretches of time.

So I learned to use the flush kit, which only allows a brief period of time between shutting the engines off after flushing, and shutting the water off. The design of our gas engines does not leave as margin for error as diesel engines seem to. One day, I took too long to shut the water off, and water filled part of the exhaust system, which resulting in a hydro locked engine. Through the solid advice of friends on this site and 'in the real world', I was able to clear everything out and avoided catastrophic damage to the engine. But after that panicked evening (and the cost of a new starter, new plugs, and bilge cleaner), I concluded that as long as I start the engines on a regular basis (usually once per week), that is better for me than risking that situation again. I live and work very close to the boat, so I am fortunate in the regard.

So, I don't use the flushing system with normal use. Since it is already installed, if I was gone for a month, I would use the flushing system prior to leaving. But I would be very quick about shutting the water off after the engines are off!

So the summary is that if you use the boat often, I would not consider a flush kit a must have. If the boat sits in the water for long periods, then the value of a flush system starts to increase. Good luck!
 
Last edited:
I think the approach to flushing is tempered with how often you use the boat, how easy your flushing system is setup, and how closely you follow directions. @b_arrington is spot on with the merits of flushing. But you need to know that there are risks as well.

When I first bought the 340, I was happy that a Perko flushing kit had already been installed on it and the previous owner was emphatic that they flushed after every outing. I learned later that the reason for this was that the guy worked on an Alaskan crabbing boat, so he was away from the boat for long stretches of time.

So I learned to use the flush kit, which only allows a brief period of time between shutting the engines off after flushing, and shutting the water off. The design of our gas engines does not leave as margin for error as diesel engines seem to. One day, I took too long to shut the water off, and water filled part of the exhaust system, which resulting in a hydro locked engine. Through the solid advice of friends on this site and 'in the real world', I was able to clear everything out and avoided catastrophic damage to the engine. But after that panicked evening (and the cost of a new starter, new plugs, and bilge cleaner), I concluded that as long as I start the engines on a regular weekly basis (usually once per week), that is better for me than risking that situation again. I live and work very close to the boat, so I am fortunate in the regard.

So, I don't use the flushing system with normal use. Since it is already installed, if I was gone for a month, I would use the flushing system prior to leaving. But I would be very quick about shutting the water off after the engines are off!

So the summary is that if you use the boat often, I would not consider a flush kit a must have. If the boat sits in the water for long periods, then the value of a flush system starts to increase. Good luck!
Never heard of anything like this. How did the water enter the cylinders?
OP use the flusher every outing
 
If the raw water impeller is in good condition, fresh water will be pushed out through the inlet (B3 leg or through hull strainer) once the engine is shut off.
 
Never heard of anything like this. How did the water enter the cylinders?
OP use the flusher every outing
If the water runs long enough with the engines off, the exhaust lift mufflers in my boat will fill. Water will look for the easiest way to get out and the increasing backpressure means that water will find an open exhaust valve.
That's why you have around 10 seconds after the engine off to turn off the water. My marina has very high water pressure (80psi), so I have less than 10 seconds.
 
If the water runs long enough with the engines off, the exhaust lift mufflers in my boat will fill. Water will look for the easiest way to get out and the increasing backpressure means that water will find an open exhaust valve.
That's why you have around 10 seconds after the engine off to turn off the water. My marina has very high water pressure (80psi), so I have less than 10 seconds.
My apologies, it says 15 seconds, but I have less, this is from the Mercruiser manual in the section on flushing:

Screenshot-2022-07-27-095525.gif
 
I think the approach to flushing is tempered with how often you use the boat, how easy your flushing system is setup, and how closely you follow directions. @b_arrington is spot on with the merits of flushing. But you need to know that there are risks as well.

When I first bought the 340, I was happy that a Perko flushing kit had already been installed on it and the previous owner was emphatic that they flushed after every outing. I learned later that the reason for this was that the guy worked on an Alaskan crabbing boat, so he was away from the boat for long stretches of time.

So I learned to use the flush kit, which only allows a brief period of time between shutting the engines off after flushing, and shutting the water off. The design of our gas engines does not leave as margin for error as diesel engines seem to. One day, I took too long to shut the water off, and water filled part of the exhaust system, which resulting in a hydro locked engine. Through the solid advice of friends on this site and 'in the real world', I was able to clear everything out and avoided catastrophic damage to the engine. But after that panicked evening (and the cost of a new starter, new plugs, and bilge cleaner), I concluded that as long as I start the engines on a regular basis (usually once per week), that is better for me than risking that situation again. I live and work very close to the boat, so I am fortunate in the regard.

So, I don't use the flushing system with normal use. Since it is already installed, if I was gone for a month, I would use the flushing system prior to leaving. But I would be very quick about shutting the water off after the engines are off!

So the summary is that if you use the boat often, I would not consider a flush kit a must have. If the boat sits in the water for long periods, then the value of a flush system starts to increase. Good luck!
I think the approach to flushing is tempered with how often you use the boat, how easy your flushing system is setup, and how closely you follow directions. @b_arrington is spot on with the merits of flushing. But you need to know that there are risks as well.

When I first bought the 340, I was happy that a Perko flushing kit had already been installed on it and the previous owner was emphatic that they flushed after every outing. I learned later that the reason for this was that the guy worked on an Alaskan crabbing boat, so he was away from the boat for long stretches of time.

So I learned to use the flush kit, which only allows a brief period of time between shutting the engines off after flushing, and shutting the water off. The design of our gas engines does not leave as margin for error as diesel engines seem to. One day, I took too long to shut the water off, and water filled part of the exhaust system, which resulting in a hydro locked engine. Through the solid advice of friends on this site and 'in the real world', I was able to clear everything out and avoided catastrophic damage to the engine. But after that panicked evening (and the cost of a new starter, new plugs, and bilge cleaner), I concluded that as long as I start the engines on a regular basis (usually once per week), that is better for me than risking that situation again. I live and work very close to the boat, so I am fortunate in the regard.

So, I don't use the flushing system with normal use. Since it is already installed, if I was gone for a month, I would use the flushing system prior to leaving. But I would be very quick about shutting the water off after the engines are off!

So the summary is that if you use the boat often, I would not consider a flush kit a must have. If the boat sits in the water for long periods, then the value of a flush system starts to increase. Good luck!
I think the risk is related to what kit you have installed, and how you use it.

Mine is a bronze strainer-top water inlet with a valve. They way I do it, I never shut off my sea cock and therefore there is no risk of either water starvation nor of overpressurization. I hook up the water, start the engine, then open the fresh water valve. I flush, then stop the engine and let the fresh water run a bit longer. That backflushes the strainer as well.

I know someone that closed their seacock to flush and kept the water running when they shut off the engine. The water pressure cracked their plastic strainer body.

There's no harm in leaving the seacock open. Sea water is not going to get up into the engine while sitting at the dock. Fresh water is lighter, so it's not going to "fall out" and be replaced with seawater. Sure, there may be some mixing at while flushing but the dilution is minimal and better than leaving the seawater in the engine.
 
"Mine is a bronze strainer-top water inlet with a valve."

Does anyone know what make/model I need to buy to add this to my seacocks?

I watched a video a while go that describes exactly what @b_arrington described; leave the seacock open.
 
"Mine is a bronze strainer-top water inlet with a valve."

Does anyone know what make/model I need to buy to add this to my seacocks?

I watched a video a while go that describes exactly what @b_arrington described; leave the seacock open.

What strainers do you have?
I have GROCO strainers and use these
https://www.sbmar.com/product/groco-arg-series-bronze-cap-with-freshwater-flush/

edit:
and I too never close my seacock when flushing. All positive pressure goes out the bottom of the boat.
 

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