Fresh water supply flow rate for Sherwood pump on CAT 3126 TA

[Marcus Teipel]

I subscribe to the value of fresh water flushing my CAT 3126 TA engines every time I return to port (the boat lives in a Salt Water environment).

 

I have purchased and installed 3 of Tony’s bronze fresh water flush caps for Groco ARG series strainers (one for each engine and one for the generator).

I consider my fresh water supply volume and pressure at the boat house to be strong (sorry no objective water flow rate data available) — I certainly don’t think its a weak water flow and would have been very happy flushing my previous trailered 454 engine with the water flow rate I get from my current dock.

 

My questions for the group arises from the following observation:

When I connect my fresh water supply hose to the bronze fresh water flush cap, and run the Cat 3126 TA at idle, and begin to close the through hull raw water supply I can see bubbles forming throughout the water canister of the Groco sea strainer. 

1).  This makes me worry that I might be supplying insufficient water supply to properly lubricate the Sherwood raw water pump?  Is this concern reasonable when the Sherwood pump is being supplied at idle by an average garden hose water supply?

2). Since the fresh water garden hose supply volume is clearly less than the water supplied by an open through hull, am I at much risk of contributing to engine and wet exhaust component overheat IF I run the engine at idle for approximately 5 minutes?

 

Thank you for your comments in advance.

— Marcus

 

Topic

[Marcus Teipel]

Thanks Gene.  

Upon reflection what you say makes perfect sense. 

[Tony Athens]

low flow dock hose & freshwater flushing

Dealing with fresh water flushing for at least 30 years has proven without any doubt that even if the dock hose only supplies 25% of what the seawater pump would normally suck at at idle, it still accomplishes the task,  you just have the run the engine a couple of minutes longer to flush out the salt water–Also because the engine load in so low,  heating has never  been  been an issue. As long as the back plate on the seawater pump stays cool, IMO you have enough water flow

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Marcus Teipel

[Gene Fuller]

The exact details probably don’t make much difference, but keep in mind that the pump RPM is generally not the same as the engine RPM.

[Marcus Teipel]

Update to CAT 3126TA Sherwood pump flow rate

My CAT 3126 TA has a Sherwood pump with a 17000 series impeller. At an idle speed of approximately 650 rpm the Sherwood 17000 series impeller should draw approximately 18-19 gallons per minute.  I have attached a reference document from Sherwood that illustrates the pump water flow.   I did a bucket test and determined that my 3/4” garden hose flows approximately 16.5 gallons per minute.   The attached video illustrates the bubbles that from when the through hull is completely closed.  The bubbles are likely cavitation “boiling” as a result of the engine driven raw water pump demanding more water flow than the garden hose can supply.   I did flush the engine with fresh water while keeping the through hull completely closed and did not notice an increase in temperature of the Sherwood raw water impeller backing plate.

[donald roth]

If there’s not enough water from the dock faucet, you’ll first see the hose collapse.  This doesn’t mean it’s not passing water though. Just that it’s drawing a suction.  It helps to use a large diameter hose and don’t choke the flow with small valves and fittings.  I’ve been flushing my motors like that for many years,  have never had any problems with impellers.  Leaving the seacock open insures no problems, like someone shutting off the hose, or hose kinking.  One thing to look at is possibly changing your HE zinc to aluminum, as it will be parked pickled in fresh water most of the time.

 

[Byron Biggs]

garden hose

yes you are getting into the pedantic area but thats ok.

The trial and error approach- inspect sherwood impeller( in practice this will be harder than writing it here),hook up garden hose, shut off thru hull, start eng at idle only and run for 10 or 20 minutes, monitor eng temps closely. Inspect impeller.  If no viable damage i would say you are good!

Eng approach-You need to have eng specs that specify minimum raw water flow at idle speed.  Probably hard to get.  As an alternative get sherwood pump specs for your pump that show flow rates vs pump rpm (guess this does not match eng rpm) and assume min value gpm (they will have liters to) is what your eng needs.  Now get a 5 or 10 gal bucket and accurately time what it takes to fill bucket.  Hopefully your garden hose gpm is greater than your min pump flow.

Now that is pedantic

Byron

 

 

 

[Marcus Teipel]

Hi Byron, 

Thank you for your reply.

 

I would like to be able to close off the seawater through hull completely in an effort to supply 100% fresh water — perhaps this approach is a little pedantic, but this is what I would like to accomplish.

I’m still wondering if I might NOT be supplying insufficient water supply to properly lubricate the Sherwood raw water pump?  Is this concern reasonable when the Sherwood pump is being supplied at idle by an average garden hose water supply?

Also,

Since the fresh water garden hose supply volume is clearly less than the water supplied by an open through hull, am I at much risk of contributing to engine and wet exhaust component overheat IF I run the engine at idle for approximately 5 minutes?

[Byron Biggs]

data missing but i would not worry

My eng 2006 QSB 5.9 380 (1000 hrs)

I made my own fresh water connections to the groco strainers but they function the same as Tony’s.

At the end of a trip I flush each eng with fresh water supplied by the marina garden hose for 3-5 minutes with the thru hull opened. I did this all season and cannot imagine my engines getting overheated at 600 rpm.

This procedure presupposes two difficult to obtain variables.  1-the pressure and flow rate from your garden hose and 2-the percent of fresh/salt water that makes it thru the eng with the thru hull opened.

With regards pressure and flow I have followed advice here and “assume” it is ok.  As far %fresh if you are concerned just close off thru hull each time.  I do not do that.

My two cents

[Author]

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