Engine Flushing Using Pressurized Dock Water

[firehoser75]

My boat (new to me last fall) came with fresh water garden hose spiggots on the top covers of the Groco sea water strainers and the previous owner used them regularly to flush the 2002 Cummins 6BTA M3 main and the Onan Gen Set. However, I am worried about this. Could there be a problem pushing pressurized dock water (pressure anywhere from 50 to 100 psi) into the running engine? Also for the 6BTA, the 5/8 inch hose is “flattened” somewhat by the demand for cooling water even at idle. If I read the specs correctly, even at idle there is normally a flow of 10 gpm. The “garden hose’ cannot provide this flow. Would it be a good idea to use an RV style pressure reducer and possibly a larger hose (3/4 inch)?
I posted this a reply to an older post, but no replies other than another forum member interested in the answer. I would like to hear whether or not my concerns have any validity or whether I should continue to use this method of flushing.
Thanks,
Tom

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[Rob Schepis]

Russ sounds like you answered your own question in that Yes you can leave the thru-hull open. After doing your flush, pull some zincs and give it a “taste test” and then you’ll know..

1 user thanked author for this post.

Russ

[Russ]

Tony, I am going to add a flushing system to my engines and plan on doing it via introducing the water thru an installed fitting in the sea strainer cap and have wondered about the need to close the thru hulls once the dock water is on and the engine running if I flush one at a time?

Assuming the fittings and fresh water supply hose continue to carry adequate volume (which they should based on the amount I get just washing her down after an outing) my reasoning is that 1) the fresh water flow at our dock seems to greatly exceed the volume of water coming out the exhaust when we have flushed the engines as part of winterization/storage on the hard, 2) the snorkel on the bottom during that process never stops spraying out the sides despite a good seat so the flow out the exhaust wouldn’t seem to be low due to lack of water from the yard supply – which is less than the flow at the dock supply, 3) the lighter fresh water will displace the salt water in the strainer before the start up and continue to displace during the flushing time after engine start due to the sheer volume so the flushing water should remain all fresh water. So in short, if the incoming supply of fresh water exceeds the engines demand wouldn’t it continue to also “flush” the sea strainer intake hose also and therefore only supply only fresh water to the engine?

[Tony Athens]

Sure it will work but is seems like quite a bit of effort to accomplish..

What most do not realize is that is does not take much water to flush the engine at an idle– Maybe 2+ GPM for a few miniutes.. Sure the pump may want a few times that, but all you have to do is keep the impeller WET and water flowing thru the engine, although it maybe be less that it would normally get from the bottom of the boat.. If the supply is low, just run the engine longer.. While flushing with a less than hi-flow hose bib or “flat hose”, just put the hand on the back of the seawater pump–If cold, then you are pumping plenty of water..

Tony

[Steve]

The method you described is much simpler…..but in theory would this work as well? Run a hose from the groco cap adapter to a large bucket in the cockpit or on the dock. Run the fresh dock water hose into the bucket as well. Close the seacock and start the engine. I’d think the raw water pump would only take from the bucket what is necessary and at the proper flow. So as long as you keep plenty of water in the bucket, wouldn’t it be the same as sucking it up the thru hull? …..or would the distance, unprimed, and uneven path of the hose from the groco to the bucket cause problems? If it did work, couldn’t you add a little salt away into the bucket to help clean the system?

[firehoser75]

Thanks for the Advice

I appreciate your help and advice. Sometimes the obvious is not so obvious (to some of us) and with experience we gain knowledge and confidence :). As usual, good advice all around.
Thanks again,
Tom

[Tony Athens]

#1 and most important when flushing an engine–NEVER pressurize the system. When you hook up the hose, the thru hull must be open.. It goes like this.

Engine OFF— Hook up the hose–Thru hull open— Turn on the hose ( water goes out the bottom of the boat so there is no pressure in the system) –Now, start the engine– then you can close the thru hull–Yes, if the hose is small and long, the hose bib is too small and / or the flow from it is too low for the engines needs, the hose will flatten–Hurts nothing as you are still getting enough water to flush the engine……

Run for a few minutes but now comes the trick — Hose off and engine off at the same time–Then OPEN the thru hull.. If you can only do one at a time, shut the hose off first and then the engine.. A few SHORT seconds of no water will hurt nothing………………..

Tricks/upgrades down the road———–Replace the HOSE BIB at the dock with a full flow ball valve–Use a shorter dedicated 3/4″ ID hose for flushing.. Be sure the attachment on the Groco strained does not restrict the water flow…….And last, never pressurize the system by having hose running w/ the engine off unless the thru-hull is open to allow water to go out the bottom of the boat————think about it..

Tony

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