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Thursday, September 27, 2007

How to change a water pump impeller...

The following was contributed by Randy Smith, owner of Attitude, a 1997 Beneteau 351 Oceanis. About 90% of overheating problems on diesel engines can be traced back to a bad raw-water impeller. Since the Yanmar 3GM30 is perhaps the most common diesel engine on mid-size sailboats built in the last 15 years, we thought it would be helpful to show you how to replace the impeller!

Even if you don't have a Yanmar 3GM30 on your boat (even if you have a
gasoline powered boat, for that matter), the impeller replacement is essentially the same on every engine. Find the raw water pump, take it apart, replace the impeller, go have a beer. Just like that!

Randy says:

The Yanmar 3GM30F is a wonderful 27 hp diesel used during the 90’s. She’s a solid performer if we stay on top of maintenance.


My Yanmar is a fresh water cooled engine, and the fresh water passes through a heat exchanger that is cooled with raw water. The most common failure of this system is the little rubber raw water pump impeller. Here’s how to replace it.

List of parts and tools:
Impeller: Yanmar part # 128296-42070 (Johnson #827)
Gasket: Yanmar part # 124233-4211
12 mm wrench
9/32” wrench
Impeller puller or needle-nosed pliers
Difficulty: Easy, less than 30 minutes.

The raw water pump has its own pulley and dedicated belt. The pump is on the forward starboard corner of your engine, or lower left as you look at the front.


It is necessary to remove the pump to get to the impeller. There are only two bolts and two hose clamps. Loosen the hose clamps (no need to remove). Remove the two bolts and lift the belt off of the pulley.


Pull the pump away from the engine far enough to spin it over so you can remove the 6 small bolts holding on the back cover. Be prepared for water from the hoses to run out of the pump when the cover is removed (Shouldn’t be more than a couple of cups).


Note the direction of the impeller flanges before pulling it out with an impeller puller or a pair of pliers. Also notice there is a key notch in the impeller when its time to install the new impeller.


Make sure the pump is clean and the pulley spins freely. Install the new impeller, again paying close attention to the direction of the flanges. I find it easier if I put a zip-tie around the impeller tight enough to get the flanges to lay over in the correct direction. The zip-tie will slip off as I push the impeller into the pump.

Using a new gasket, replace the cover and tighten the six small bolts. Spin the pump back around and slide the belt over the pulley. (Make sure it’s in the correct groove on the main pulley.) Install the two bolts, and adjust the belt as you tighten the bolts. Don’t forget to tighten the hose clamps.

I like to finish by cleaning out the strainer and filling up the hose with some water. It’s now time to fire up the engine and look for leaks!



For complete instructions on changing water pump impellers and any and all other repairs to Yanmar diesel engines, the new Yanmar shop manual was released on August 21, 2010. YOU CAN BUY YOUR COPY HERE.

12 comments:

Julian said...

Usually need to clean up the mating surfaces and remove any crud from the input side or it will break away and could damage the impeller at a later date. A little waterproof grease on the gasket may improve the seal. Worth changing annually, though my impeller shows little wear at the end of the year, as this is not an easy job at sea when you may be relying on your engine - else why is it on??

Anonymous said...

I've seen instructions for this process in a couple of places and both have advised to close the raw water valve prior to the procedure. Any thoughts?

Dave Guilford said...

Yes, you should always close your seacock before this procedure. I think it's important to mention this also, especially if you own an older boat: go through every seacock on your boat at least twice a year and open and close them several times. They have a tendency to freeze over time, and I've had them literally break off in my hand at the worst possible times.

Anonymous said...

You don't need to memorize the direction of the wheel bend (unless you are, like most North Americans, into color-coding and table-lookuping). Understand how it works once, and for the rest of your life you will never curse yourself for forgetting to mark the direction of rotation. Here is how it works: it squeezes water out before approaching the narrowing (where the segment is welded inside the cylinder) and expands, sucking water, when exiting the narrowing. The intake is where it sucks, the exit is where it squeezes. Since you know for sure where the water comes from (seacock) and where it goes (engine) you can figure out which direction the wheel rotates).

Jacob said...

Hello
Thank you for useful instrucation, Keep sharing informative stuff. I would like to hear more from you.

fullkeel said...

No one has mentioned retaining or replacing the key on the shaft?

jce.daams said...

Very interesting to view all the photos and read all the comments. Especially the comment of anonymous explaining how the water pump works. The explanation is accurate and to my opinion correct, it also contradicts the last picture of Randy's photo session: the flanges of the impeller point in the wrong direction!!

plumbing said...

If you are not comfortable with taking these measurements, you can always purchase a water fountain kit that contains all the necessary parts that are guaranteed to work properly with one another. This is always a great option if money is less of an issue or your aren’t concerned with getting the most efficiently tweaked system possible.

Anonymous said...

No, Randy's impeller is correctly installed as shown in the picture.
Contact me for further discussion.
rick10@tds.net

Anonymous said...

Apologies to Jce Daams, the flanges are in the wrong direction on the impeller in the picture showing the open impeller with the orange bucket below it. Noting that the coolant flow is from left to right, and that the impeller direction in this view is CCW due to the impeller assembly being turned inside out for the picture. When assembled it rotates CW same as the engine rotation.

plumbing said...

impeller shows little wear at the end of the year, as this is not an easy job at sea when you may be relying on your engine. How it works: it squeezes water out before approaching the narrowing (where the segment is welded inside the cylinder) and expands, sucking water, when exiting the narrowing.

solosailor said...

A related question: my engine is overheating, little evidence of water exiting with exhaust. Impeller is fine but the flywheel powering it is not turning. Suggestions please we have a good forecast this weekend!