Power of 2GM20 raw water pump? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Old 10-01-2013
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Power of 2GM20 raw water pump?

I installed a T in front of the raw water filter which I use to flush my 2GM20R. On the way back to the dock, I fill several buckets with fresh water in the cockpit and let gravity supply the pressure to get the water through a garden hose, down to the motor at the T. Works like a charm but it's a pain to stop and get the water.

Decided to use the fresh water tank that supplies the forward sink, instead of the buckets. The tank is at about at the same level the motor, maybe slightly higher. If I fill the tank, the 3" fill hose which runs from the tank up to the deck supplies enough pressure to start water flowing through the garden hose to the T. Obviously, this pressure would drop as the water level goes down into the tank. I've used the system twice and it seems to work well.

Here is my question: Does the raw water pump supply enough pressure (suction) to draw the water through about 10 feet of hose from a tank at the same level? Obviously it does, as I've done it, but could I harm the pump doing this?

BTW, If you're wondering why I don't simply flush the motor out at the dock, I hate idling to do it, and would rather do it with the motor under load. Besides...It's one less thing to do at the dock!

Last edited by L124C; 10-01-2013 at 06:41 PM.
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Old 10-01-2013
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Re: Power of 2GM20 raw water pump?

Get yourself a cheapo IR thermometer. Take a few readings (head, block, exhaust elbow, cooling water effluent, et cetera) with seawater flowing through the system, switch over to fresh water and repeat the reading after a few minutes. You may have to refill your FW supply a time or two, but let it run long enough to get a significant effect (if there is one). If the temps haven't jumped up more than a few degrees (and I bet they won't) you're golden. My guess is that whatever reduction there is in flow will be more than compensated for by the engine's thermostat. As far as damaging the pump, whatever added stress the FW intake setup might be causing, it can't be any more that the added stress the pump endures while operating at WOT.
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Last edited by SlowButSteady; 10-01-2013 at 06:30 PM.
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Old 10-02-2013
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Re: Power of 2GM20 raw water pump?

I have set up my 2GM with a similar T piece, but do flush it at the dock. When done I pull the hose off at the dock tap with the engine still running and walk back to shut the engine down. The aim is to ensure that no water under pressure ends up in the wrong place, like the cylinders, but to also time the shut down so the impeller does not run dry.
The pump has enough grunt to draw all the water through the hose, which is some 50 feet long and not that much above the engine once I drop it off the tap, so I reckon yours will be fine drawing water from your sink supply.
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Re: Power of 2GM20 raw water pump?

Quote:
Originally Posted by arvicola-amphibius View Post
I have set up my 2GM with a similar T piece, but do flush it at the dock. When done I pull the hose off at the dock tap with the engine still running and walk back to shut the engine down. The aim is to ensure that no water under pressure ends up in the wrong place, like the cylinders, but to also time the shut down so the impeller does not run dry.
The pump has enough grunt to draw all the water through the hose, which is some 50 feet long and not that much above the engine once I drop it off the tap, so I reckon yours will be fine drawing water from your sink supply.
If I understand you correctly, the drop from the hose on the dock to your motor must be at least four feet. More than enough for a good siphon (similar to the pressure via the raw water intake and my bucket system). Not so in my case.
Before I devised the bucket system I was advised against pressuring the cooling system directly from the hose spigot, as water can still end up "in the wrong place". Search for the thread here if interested.

Last edited by L124C; 10-02-2013 at 04:44 AM.
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Re: Power of 2GM20 raw water pump?

Yeh, I suppose there is a bit of a siphon effect helping it, though not much as the dock floats about 18 inches above the boat's waterline, and the hose must climb up over the deck first.
I am very careful not to apply too much pressure, and don't put the tap on, or let it run, at any time the engine is not running.
Anyway I used this method on my previous Yanmars and a Perkins with no ill effect.
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