raw water coolant flow rate at idle??

[james]

This is a question which may cause me to modify my fresh water flushing approach. First, if anyone can check my calculation, that would be great. Per a spec sheet I have for a C series 400 engine, raw water flow is 63 gpm (assuming that number is at rated rpm. So, doing the math, I calculate a flow of 14.5 gpm 18.7 gpm at an idle of 750 rpm.

A calculator I found online indicates that my city water connection via 5/8th’s 50 foot hose at 40 PSI will deliver 22 gallons a minute. Both those numbers seem high to me, but the math is correct.

Currently my freshwater flushing technique involves attaching a hose to the strainer, opening a fresh water input valve, starting the engine, then closing the thru hull.

If the above calculations make sense, I eliminate closing the boat raw water intake thru hull. That makes things a little simpler and eliminates 1 trip up and down the engine room ladder.

thoughts?

Topic

[marks737]

Rob,

This is my first winter with this boat and Cummins engines. I’ll try flushing both ways next season and see what happens. Thanks!

[Rob Schepis]

Mark, have you ever completed your flush with the seacocks left open and compared that which is being left behind in your coolers?

[marks737]

I have flush fittings on all 3 strainer caps. I bought a shorter length hose with a fitting and valve that connects to the strainer fitting and on the other end which I hold at the helm also with a valve fitting so I can reach the ignition switches and control the water shut off/on at the same time.

So my flush procedure is: 1. Close sea cocks. 2. connect hose to flush fitting on strainer cap. 3. Make sure hose valve at helm is closed. 4. Turn dockside water valve on. 5. Back at helm, simultaneously start engine and open hose valve fitting. When finished flushing, simultaneously close hose valve and shut down engine.

Note: The extra valve that’s installed at the end of the hose right at the strainer fitting allows me to close it so I can remove the hose from strainer without all the excess water that’s in the hose running out. Also, having the valve on the hose near the helm allows me to use the salt away bottle as well.

Hope I didn’t confuse anyone! I’ll have to add pictures sometime.

[Tony Athens]

SaltAway–IMO and waste of $$ and effort.

Even if your dock hose is 25-50% of the flow that pump wants to ask for at idle, , it does not matter–You can still get a 100% flush if you set it up right and UNDERSTAND the principles involved.

Tony

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David O

[David O]

Hi All,
I have 6BTA5.9M3 370HP engines. Anyone know if a standard (fairly good pressured) marina hose will provide enough freshwater to flush the engine at idle?
I don’t really want to go to the expense of fitting the flushing fittings if its not going to work!

The other alternative is for me to fit a salt-a-way fitting. I feel that this would be a distant second option.
Does anyone recommend salt-a-way flushing or is it a waste of time? (Should I not be able to use freshwater).

Any advice is greatly appreciated.

Cheers
David

[james]

I'll add one more thought

I always run the fresh water out through the strainer for a while when the engine is off. That flushes the line from strainer to thru hull and fills it with fresh water. Fresh water is lighter than salt water so it stays in that hose. guess what? Zero marine growth in the hose. As you can tell, I have a lot of passion about this for engine preservation. My friends at the docks think I’m going overboard, but I can assure you my maintenance bills tend to be about 1/2 theirs.

[David R Flamer]

I can’t argue with that

I set up a Y valve with separate shut offs and some braided s/s hose to the valves at the strainers. With another shut off valve on the hose itself it is pretty easy to be smooth with the water flow at shut down. With all of the shut offs, it’s pretty hard to leave something open.

Engine room start and stop switches would be pretty cool for this purpose. It would then be a one-person operation.

Another note: After the engines are flushed, I make sure to shut off the keyed master ignition switch and then hang the key on the sea cock lever. Remembering to get the valves open is never an issue. I also put signage on the bridge at the start switches as a second reminder (or in an emergency if the operator was not me) to get the sea cocks opened before the engines are lit the next time.

[Philip]

Even if you don’t shut you thru hull you are diluting any salt water significantly and will see great benefits – arguably the same as shutting the thru hull. Although you may not be getting a perfect 100% fresh water flush your math supports that you will have more fresh than salt water and when the engine shuts down you will not pressurize your salterwater pump as the fresh water will just go out the open thru hull. Just a little less valve movement….

For those that don’t fresh water flush you should consider it – you will never find anyone that fresh water flushed that says anything but positive benefits – cooling system stays healthy, zincs last much longer, coolers that have been serviced last longer between maintenance and come apart easily.

Phil

[james]

Further description on my process

David – good points about over pressuring the raw water circuit. My approach is a bit different as I am doing this solo. When my flush period, usually 10 minutes is done, I grab a bunch of extra hose, and fold it shut as I kill the engine, then I climb back down and reset all the valves.

Another thing which I’ve done which really makes it easier, is I screw a quick connect fitting onto the flush valve, then use that to connect the hose. That eliminates having to twist the hose while you get it attached in a tight engine room.

For safety, I’ve added a cap which I screw onto the valve, that way if I forget to close the flushing valve, I won’t have a water flow issue.

The benefits of the flushing really showed this last maintenance cycle. The aftercoolers, which had been heavily greased two years previously, came apart with hand pressure. We replaced the exhaust elbows, which were 20+ years old, and put new ones on with a dry section leading to a down hill down pointing shower. The Turbo’s looked great as well. No salt mist sitting around them.

[David R Flamer]

I still think you need to close the raw water intake if you want to ensure that fresh water only is introduced in to the raw water circuit.

I rigged up a system where I flush both engines simultaneously. While the fresh water pressure at my dock is pretty impressive, I am sure that I am not supplying 100% of the volume that each engine is drawing.

That said, the engines are not under load. I have checked the backing plates to the raw water pumps during this flush procedure and they do not get anywhere near warm. I am sure that there is plenty of water getting to the pumps.

If someone things otherwise, I am all ears.

My procedure does take two people however. When I am done flushing , the hose valve needs to be shut off at the same time as the engines are shut down or there would be too much pressure in the raw water circuit.

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Tony Athens

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