Water Pump Impeller Service Interval On Small Outboard Engines

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Author Topic:   Water Pump Impeller Service Interval On Small Outboard Engines

project13 posted 10-26-2009 02:26 PM ET (US)
I have had my [Yamhama 40-HP outboard motor] for five seasons and [running time of] around 250-hours. I [think] it is time to [service] the water pump impeller, but I wonder if [water pump impeller replacement] is necessary with a smaller motor, in the way it is with larger motor. Any thoughts would be appreciated. Thanks.
merc125 posted 10-26-2009 03:57 PM ET (US)
Probably not needed, but I would would do it just to make sure it comes apart, lube drive shaft into crank, and put never seize the on the bolts during reassembly. MartyD
jimh posted 10-26-2009 07:01 PM ET (US)
A good friend has a Yamaha 150-HP engine and I believe he went over ten seasons using the same water pump impeller. I think he just finally had it changed as a preventative measure; the original water pump impeller was still working. The water pump impeller in a Yamaha engine seems to be a component with a much longer life than you find in some other brands. Five years is not an unusual life span for a Yamaha.
I don't know how the engine horsepower factors into the equation of predicting the life span of the water pump impeller. The same rubber is probably used in the impeller in a 40-HP engine as in a 250-HP engine.
GRAND NUSSIE posted 10-27-2009 07:19 AM ET (US)
I got 17 years on the impeller on my 90 Yamaha. At that point, the pump was not working well at low speeds. But no "blades" broken off. I DON'T RECOMMEND YOU WAIT THAT LONG!
My 8 hp Merc is now 20 years old with the same impeller. Yes, I am worried. Yes, I plan to change the impeller as a winter project.
Dick
brisboats posted 10-27-2009 09:02 AM ET (US)
If it has been five years it is time. Even if the water pump impeller is still in good condition removing and replacing the lower unit every so often assures that you can service the water pump easily should it stop pumping. Every motor has different characteristics. I drop the lowers annually on my Merc V-6's the impellers in them seem to wear quickly and I want the peace of mind of a new one each season. My 10 year old kicker is on the original pump, looks like I need to at least drop the lower on that one over the Winter.
Brian
tedious posted 10-27-2009 09:41 AM ET (US)
The issue is not the water pump itself, it's getting the lower unit off to service it! If you go too long, you're going to have corrosion / frozen bolts / etc. I have a neighbor in Maine who hasn't had the lower unit removed in 15 years, and I am guessing it's going to be quite an adventure when it eventually needs to come off.
Tim
Tohsgib posted 10-27-2009 09:43 AM ET (US)
If you don't want to repaint your engine from the burn marks the torch left on it to remove your bolts, I recommend you at least remove them, add some grease and reinstall.
kwik_wurk posted 10-27-2009 10:59 AM ET (US)
As mentioned the bolts are the damning part.
On smaller units (10 hp or less) I have found that even if the impeller looses half it's blades you still get enough dribble water to cool the engine. Assuming you are aware of the cooling water tell-tale and what it's doing. (This is not true with higher velocity cooling systems on 40 hp and above. These engines need a lot more volume running through the system.)
The life of the impellers has always baffled me. I have only replaced one impeller on my kickers. I have opened them up several times, and put silicon grease on them and that's it. (Some are 12 years old.) -- However on my larger Cummins engines I find the impellers start to crack/tear after 2-3 years (~300 hrs).
The 90 Merc. goes in to the mechanic every 3-4 years because that is the frequency of a mechanical bug that I don't want to deal with. At that time I have the impeller replaced because it's a convenience.

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Author	Topic: Water Pump Impeller Service Interval On Small Outboard Engines
project13	posted 10-26-2009 02:26 PM ET (US) I have had my [Yamhama 40-HP outboard motor] for five seasons and [running time of] around 250-hours. I [think] it is time to [service] the water pump impeller, but I wonder if [water pump impeller replacement] is necessary with a smaller motor, in the way it is with larger motor. Any thoughts would be appreciated. Thanks.
merc125	posted 10-26-2009 03:57 PM ET (US) Probably not needed, but I would would do it just to make sure it comes apart, lube drive shaft into crank, and put never seize the on the bolts during reassembly. MartyD
jimh	posted 10-26-2009 07:01 PM ET (US) A good friend has a Yamaha 150-HP engine and I believe he went over ten seasons using the same water pump impeller. I think he just finally had it changed as a preventative measure; the original water pump impeller was still working. The water pump impeller in a Yamaha engine seems to be a component with a much longer life than you find in some other brands. Five years is not an unusual life span for a Yamaha. I don't know how the engine horsepower factors into the equation of predicting the life span of the water pump impeller. The same rubber is probably used in the impeller in a 40-HP engine as in a 250-HP engine.
GRAND NUSSIE	posted 10-27-2009 07:19 AM ET (US) I got 17 years on the impeller on my 90 Yamaha. At that point, the pump was not working well at low speeds. But no "blades" broken off. I DON'T RECOMMEND YOU WAIT THAT LONG! My 8 hp Merc is now 20 years old with the same impeller. Yes, I am worried. Yes, I plan to change the impeller as a winter project. Dick
brisboats	posted 10-27-2009 09:02 AM ET (US) If it has been five years it is time. Even if the water pump impeller is still in good condition removing and replacing the lower unit every so often assures that you can service the water pump easily should it stop pumping. Every motor has different characteristics. I drop the lowers annually on my Merc V-6's the impellers in them seem to wear quickly and I want the peace of mind of a new one each season. My 10 year old kicker is on the original pump, looks like I need to at least drop the lower on that one over the Winter. Brian
tedious	posted 10-27-2009 09:41 AM ET (US) The issue is not the water pump itself, it's getting the lower unit off to service it! If you go too long, you're going to have corrosion / frozen bolts / etc. I have a neighbor in Maine who hasn't had the lower unit removed in 15 years, and I am guessing it's going to be quite an adventure when it eventually needs to come off. Tim
Tohsgib	posted 10-27-2009 09:43 AM ET (US) If you don't want to repaint your engine from the burn marks the torch left on it to remove your bolts, I recommend you at least remove them, add some grease and reinstall.
kwik_wurk	posted 10-27-2009 10:59 AM ET (US) As mentioned the bolts are the damning part. On smaller units (10 hp or less) I have found that even if the impeller looses half it's blades you still get enough dribble water to cool the engine. Assuming you are aware of the cooling water tell-tale and what it's doing. (This is not true with higher velocity cooling systems on 40 hp and above. These engines need a lot more volume running through the system.) The life of the impellers has always baffled me. I have only replaced one impeller on my kickers. I have opened them up several times, and put silicon grease on them and that's it. (Some are 12 years old.) -- However on my larger Cummins engines I find the impellers start to crack/tear after 2-3 years (~300 hrs). The 90 Merc. goes in to the mechanic every 3-4 years because that is the frequency of a mechanical bug that I don't want to deal with. At that time I have the impeller replaced because it's a convenience.