Raw Water Pump Replacement Options

[Blackacre]

I'm looking for some troubleshooting advice pertaining to my Yanmar 3GM engine on my 1986 Hunter H34.

Last year I cleaned out & replaced the impeller and gasket on the raw water pump because the engine was overheating (see pictures). The impeller was destroyed (broke into small pieces). I thought the problem was fixed but now about 40 engine hours later I'm having the same problem. I replaced the impeller again but the engine continues to overheat. I confirmed the following;

- swam under the boat and cleared out the water intake seacock.
- Opened and shut the seacock valve and opened the relief valve and water flows out.
- Cleaned out the sea strainer
- Ran the engine with pump attached and then disconnected the water line running to the engine and no water was flowing.
- Blown air backward through the line connecting to the water pump inlet and the line was free and clear.


Questions;

- Is it possible that the pump is simply not creating enough suction. Possibly due to scarring along the inside walls of the pump?
- is the sea strainer a possible problem and should I replace it with a modern style?
- if I do replace the pump assembly should I replace it with the OEM or is there a better alternative?
- should I flush out the heat exchanger and if so how could I do that? It appears to me that I would disconnect day water hose and blow out the line in the same direction that the water pump flows or should I go in reverse?
- I'm aware of the two different pump styles based on the year. Mind is the one with a paper gasket and a pin that holds the impeller in place. the other style appears to have a screw through the shaft of the impeller. Is that a better alternative?

Assumptions:

- My best guess is the pump is running dry which causes the impeller to overheat and fails. I don't yet know why the pump is running dry.

 

[joker460]

Have you disconnected the inlet hose at the pump and looked for water flow when you open the water intake valve? There may be air in the intake side.

 

[Allan12210]

Check to make sure the sea strainer lid is evenly tightened and not sucking air. Sometimes I have tightened one side of the lid more than the other and it results in a stream of bubbles causing the pump to lose prime. You might need a new cork gasket in that lid. Tighten evenly.

Regarding cleaning the heat exchanger...after closing the seacock, drain the seawater from the exchanger via the little valve on the back of it. You can then pull the front cap and see the end of the exchanger tubes. I use a 1/4" by 16" long drill bit to clean the individual tubes running the drill motor slowly and pulling back and forth every inch. Don,t go through the back.The drill is just undersize enough to remove a considerable amount of scale but not cut through the sides. You should be able to reuse the same cap gasket and close it back up. I don'think this affects your pump failure but is good maintenance for later.

 

[ice breaker]

On our Fisher Panda, we started to loose prime to the cooling pump after leaving the boat for a week. There is a rubber shaft seal ( that I was not aware of) on the inside pump shaft. Once you over heat the pump this seal is likely melted and will need to be replaced. Once we replaced the seal we have not had any problems since. I am not sure if your pump is built this way or not, but it would be worth looking at. We have a Johnson pump on the FP gen set.

 

[Blackacre]

Have you disconnected the inlet hose at the pump and looked for water flow when you open the water intake valve? There may be air in the intake side.

Yes I did. No water. does this mean this is a blockage? How much water should be coming through the hose and sea strainer?

 

[Dan Johnson]

If...

you remove the hose from the thru-hull and open the valve, you should have a gusher about 4 inches tall. If not, run a round file or something else (Phillips head screwdriver) down the valve when open, or use compressed air (tire inflator, etc) to blow out any debris. I've had a plastic bag and weed sucked up and a mud dauber nest built over the winter that blocked water flow. If you're eating impellers, it's a water flow problem, which also leads to the next issue--the heat exchanger.

Allan covered how to clean out the heat exchanger. When you open up the front cover, you may find inpeller pieces--they could be blocking water flow and causing the overheating.

 

[Blackacre]

Thanks for the advice. I didn't realize that I needed to prime the raw water pump. How do I do this? I assumed it would self prime. Why won't air work its way though the system?

I will check the sea water strainer and gasket to make sure I'm not sucking any air.

Does anyone have an opinion about back flushing the hoses running to and from the sea water strainer and possibly the heat exchanger?

 

[rfrye1]

Raw water blockage.

I had a similar issue with raw water blockage. Working backwards, I found a small fish had been sucked up pass the thru-hull and was in the hose between the thru hull and the strainer.

Bob.

 

[Blackacre]

Today I cleared out the intake lines, sea cock and flushed out the heat exchanger. I'm not sure if there was a blockage but I can confirm that there isn't anything in there now.


Next steps;

I plan on cleaning and reinstalling my sea strainer with new gaskets. The old gaskets were in bad shape but not likely leaking very much.

The attached pictures are of the current raw water pump and impeller. When reinstalled if the problem continues I will replace the pump. I read a few other post about the cam of the pump getting warn out and losing suction. When and if I need a new pump I plan on replacing this pump with the newer version which is said to be more powerful.

Engine Yanmar 3GM30 (F) "Pre EUR Model"
New Version: Johnson Pump F4B-903, 10-24509-01. Impeller Johnson 810B

 

[Blackacre]

One more issue. I want to replace the raw water pump but I understand that Yanmar changed the water pump on the 3GM30F engine around 1997 when they switched manufacturing over to the EU. The engine serial numbers start with an E if built after 1997 and is also indicated with a -YEU after the number such as 3GM30F-YEU.

I would like to know if the new water pump will fit on my only engine fro 1986.

I believe this same issue pertains to the 2GM20F engine

 

[joker460]

Give these guys a call: http://www.depcopump.com/catalogs.php

They supply the pumps for a very reasonable price and they are very helpful.

 

[Claude L.-Auger]

Looking at the first picture makes me wonder if the cover is showing enough wear and tear to create a void and prevent the impeller from doing its job correctly. You could try to clean the back side of the cover and put it on the pump with a new gasket. Worked for me on my 3GM30F. Good luck

 

[Blackacre]

Everything is back in the boat and there doesn't appear to be any issues with the pump.

I also notice that there is a purge valve on the backside of the heat exchanger. Opening this valve allows the water to Passthrough and what I assume is to remove any air caught in the system. I ran the engine with this valve open until there was a steady stream of water with no air bubbles coming out the hose.

I downloaded the detailed specs of the new pump and compared it to the old pump. The only difference appears to be where the hoses connect. Otherwise the specs appear to be the exact same. I plan on buying the new pump and installing it keeping the old pump for a backup. I'll update this posting for others.

Attached is a few pictures of the sea strainer I cleaned out with vinegar and baking soda. As well as the valve noted above.

 

[Blackacre]

Looking at the first picture makes me wonder if the cover is showing enough wear and tear to create a void and prevent the impeller from doing its job correctly. You could try to clean the back side of the cover and put it on the pump with a new gasket. Worked for me on my 3GM30F. Good luck

Thanks for the tip. I polished the cover and installed a new gasket with the last impeller. I just think the pumps cam is worn out and it's losing suction. Still works for now though.

 

[joker460]

You may also want to add a speed seal. It saved me on many occasions when I was experimenting with rotating the orientation of the pump. You can see it on my pump modifications here http://beneteau.sailboatowners.com/...d=259&cat_id=182&aid=8165&page=article&mn=352

Good to hear everything worked out.

 

[splax]

You need to have the belt tensioned correctly or the pump will not cause the water to flow. The belt itself has to be in good condition. replacing the belt and impeller every couple years is not a bad policy.

 

[Blackacre]

You need to have the belt tensioned correctly or the pump will not cause the water to flow. The belt itself has to be in good condition. replacing the belt and impeller every couple years is not a bad policy.

How does one correctly tension the belt? The Yanmar dealer said to just put a firm pressure on it and tighten down the bolts. I would say I have less then 1" of play on my pump belt and just over 1" on the main belt. I would imagine over tensioning the belts and can damage the bearings and pulley assembly and two little tension can risk damaging the belt itself.

I agree, new belts are cheep insurance. I also carry with me a spar set and spare impeller.

The fast access conversion Joker mentioned is a nice feature.

 

[splax]

Blackacre,
I thought I had tensioned mine correctly after I examined the impeller while underway, but I was wrong. After restarting I got the temperature alarm, then saw the belt wasn't turning well enough. I used a tool handle to tension the pulley very firmly and tightened the nut. The belt still had 1/4-1/2" play. I use the green belts from NAPA, high quality and less expensive.

 

[Dan Johnson]

H34 3GM30F Raw water pump option...

After seasons of removals, the Phillips head srews that hold the back plate to the pump housing were pretty well stripped out. I replaced them with 4mm SS bolts with lock washers (they did have to be shortened with a Dremel cut-off disk). Wanted to use hex set screws but couldn't find what I wanted. Just a thought...

 

[kloudie1]

Exactly, Dan.. I found the correct size, even, at my local Ace Hardware..