Volvo Penta D4 (& D6) Fresh water flushing

[npm108]

For DPH flushing , I tape off the main inlets and then have used a piece of 15mm HEP20 (Acorn) plastic plumbing pipe which has a connector to a hose pipe quick disconnect. Simply push that up the inlet hole at the bottom of the DPH drive (15mm) is a perfect fit and you have your out of the water flush solution

 

[ss2016]

I have a VP D6-400/DPI. It has 300 hours after 4 years. The boat sits in English Channel salt water April to October. I am wondering if I really should rig up a system to flush the system through with fresh water every few weeks especially when its NOT going to be used for a couple of weeks or more. I will never be one of the 'enthusiasts' who does this every time the boat is used, but then I note that no one in my marina seems to do it.
So, my question is this. Are a few flushes during the summer going to SIGNIFICANTLY defer raw water system maintenance problems later in the engines life, or are they just making work? The engine is of course fully flushed/antifreezed at the end of each season. It is also designed to operate in salt water.
A subsiiary question. If I decide to implement a system I can introduce water at the strainer which sits before the impeller. The pontoon hose supplies a steady flow but not as fast as the impeller sucks it in on tickover. I presume that provided there is flow no harm will be done to the impeller or the elbow particularly if done on a cold engine. Is this correct?

PS I really dont want to install a VP Nutri Salt system.

 

[kashurst]

I found it worth doing if I knew I wasn't going to be using the boat for a few months. It gets the salt water out and slows build up of deposits.
Ideally you need the fresh water feed from the hose pipe to keep up with the engine throughput. I used a 25 litre container as a buffer tank, filled it first with water, then start the engine and let it consume water as fast as it wants - which was a bit quicker than the hose flow. So with the hose filling the buffer tank it will still ultimately empty the buffer tank. However by that time a lot of fresh water has gone through the system. So I used to switch the engine off when there was about 20% left in the buffer tank. I used this set up to winterise the engines - except obviously put an anti freeze mix in the tank and didnt refill it.

On the last boat it was easy to pull off a hose to the gearbox cooler as it was the first point sea water goes into the engine. On a previous boat I made a polycarbonate disk with a skin fitting and hose etc that fitted into the sea water strainer, replacing the normal plastic top.

 

[MapisM]

I am wondering if I really should rig up a system to flush the system through with fresh water every few weeks especially when its NOT going to be used for a couple of weeks or more.
I will never be one of the 'enthusiasts' who does this every time the boat is used, but then I note that no one in my marina seems to do it.

Agreed, fresh water flushing while the boat is being used regularly is way OTT and bound to make no meaningful difference.
As a rule of thumb, I also do it when I don't plan to use the boat for at least a couple of weeks.

Ref. the first of your questions, I'm not aware of any "scientific" test comparing engines wear of flushed vs. non-flushed boats, but having owned several boats on the lake, I can be positive that in the long run salt does make a difference.
And not only to engines, BTW: I installed the "BodgeFlow" (as the forum eventually christened the flush system - long story!) also on the genset, the airco chiller, and even the shaft seals.
In other words, after flushing everything, I have no salt water anywhere inside the boat - something I very much like.

Now, it's true that this creates a bit of work, but a good preparation makes a massive difference.
For instance, I had genset/chiller/shaft seals directly connected to the pressurized onboard fresh water circuit, and all I have to do for flushing each of them is close one valve and open another.
For the engines instead, initially I also attached a hose from the dock supply to the strainer, but afterwards I upgraded that with a T installed along the main fresh water pipe going from the tank to the pump, with a large-ish (1") diameter flexible pipe and a quick coupling connector, attaching that to the strainer.
This way, the engine impeller sucks as much water as it demands while flushing, and all I have to do is move this pipe to the other engine when I'm done with the first one, which takes less than a minute.
If you would want to optimize that even further, you could have two of these pipes, leaving them permanently connected to the strainers and reducing the work to turning a valve.
The reason why I preferred NOT to do that (aside from being only marginally more efficient) is that my strainers are near the e/r entrance, and pipes permanently attached would have been a bit in the way of access - but YMMV.

This direct connection to the boat fresh water tank addresses also your last question on the flow capacity, which is plenty enough when running the engines at idle.
That said, I never had any problem also when I used a dock hose for flushing the engines.
But in this case, be sure to have a strong enough hose, that doesn't squeeze if and when the impeller wants to draw more water than the dock can supply.
Otherwise, you risk to get the flow restricted, potentially even blocked, which is bound to make no good to the impeller and the rest of the cooling system if you don't notice that promptly and shut the engine down!

 

[ss2016]

Thank you both! Two really helpful posts. I will get a polycarbonate extra cover made up for the strainer and I like the idea of the buffer tank. That had not occurred to me. It would be nice to use the boats own fresh water tank but I will have to investigate how practical that would be.

(If I were ordering a new boat again a few simple mods and some intelligence from VP would make this so simple!)

 

[ingenious]

Interested in this as I do have a VP Nutri-salt fitted which I have Ben religiously giving the 45 second burst at the end of each day's use and it fairly eats up the €50 a litre additive.