replacing impellers before they break ?

J

jmunro123

Member
Feb 2, 2008
370
Gran Bend, Great Lakes
Boat Info
2004 Sea Ray 390 Motor Yacht
Engines
8.1's
I was reading a magazine about things you can fix before they break. One of the suggestions was to replace the impellers. however it did not say when. Our boat is a 2004 with about 140 hours on her. What is the suggested replacement time. The boat is in fresh water 6 months of the year.
 
Good practice is to purchase and follow the correct factory service manual.

It is inappropriate to perform service without those documents, without the correct tools, without appropriate knowledge or without appropriate experience.

On-line information is useful, but should not override the FSM.
 
I will be replacing my raw water impellers for the first time this year. I can only speak for fresh water boating. My experience has been I can get 3 years of service life out of my impellers. For me, that is around 200 hrs of use for the way I use the boat. HOWEVER, if you frequent shallow water running to approach a beach, where you are churning up the bottom, your water pumps are also sand and silt pumps.

My slip neighbor last year had 5 years on his 5.0's when he received an overtemp alarm. When the Technician pulled his raw water pump, there were no vanes left it looked like a rotor....which meant to me that 20 hrs prior to their failure, they could still pump some water to satisfy the engine temp. He uses his boat in shallow water each outing.

I would say you're due...if nothing else see what you have and replace them while you're there....whether you DIY or not. Depending on what type of cooling system you have, back flushing a heat exchanger on a close cooled system to get the vanes out can't be any fun.

ps - nice looking boat! Is that a sun screen over your windshield?
 
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Thanks Jeff for the advice. Yes that is a sun screen around the front windsheild. We don't use it that often but it does come in handy if we are tied up and want some extra privacy.
That advice is what I was looking for , I had no idea how long the impellers usually last. I will check the owners manual and talk to the mechanic. The boat will be commissioned in about 3 weeks and that should give me enough time to get any parts required.

Thanks
 
Every other year has been my practice. My 2004 has had three changes already. In my 5.0, it's off with two hoses, pull the belt off, three bolts and the pump is in my hand. Six screws, backer plate off, impeller out, impeller in, shot of WD-40 to prevent a dry start, new o-ring gasket, backer plate on, pump into place. It can be done pretty quickly, if the motor is cool and you're not rocking and rolling in a southerly here in Long Island Sound. I can do it in 20-30 mins. with the boat on land.

I always carry a spare so if I have to change it underway I could. If you have to do it in the water, just watch your waterline and intake hose. Under the right conditions, you can set-up a siphon on the intake line. You'll get that sudden shot of fear with lots of water puring through a 1 1/4 inch line into the bilge. :smt101:smt101:smt101
 
There was an entertaining discussion on this a while back here:

http://clubsearay.com/forum/showthread.php?t=15754

You may want to ignore the idiotic "mine are only replaced when they fail" advice... I doubt that's in any manual.

You are pretty lucky if you've got the original impellers in the pumps. However, if you have pieces missing, you are going to need to fish them out of the heat exchangers downstream. That's why it's good to change them before they start falling apart.
 
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wingless said:
Good practice is to purchase and follow the correct factory service manual.
Click to expand...

Good advice here but it contradicts what you said here!

wingless said:
Mine are only replaced when they fail. I split the raw water system and pulse flush the broken bits out of the heat exchangers.
Click to expand...

My factory service manual states to "Disassemble and inspect the seawater pump and replace worn components Every 300 hours or 3 years"

Congrats, you've learned a lot since February 26th!
 
FWIW - I rebuilt my raw water pump (raw water cooled in salt water 6 months) with new impeller w/plastic housing (merc stuff) 2 years ago. This would be the third year so when I pulled it apart yesterday - I was shocked that the impeller basically had taken such a set. It would probably cool, but I never chance it so I usually change them every two years (approx 200 hrs) - needed or not. I was also surprised that the salt water had eaten my housing and am needing to rebuild or replace the housing again.

If you replace the impellers only, look very carefully in the housing for nicks or chunks missing where the impeller blades travel. For a hundred bucks it makes more sense to replace the impeller and plastic housing.

Mark
 
Even though most pump manufacturers give a time period (or hours) to "inspect and replace worn parts" for the pump, many of them also state in the manual to remove the impeller if the boat is being winterized or sitting for a long time so it doesn't develop a set. Most people ignore that advice and just see the "every two years" part.

My manual actually says to pull the impeller every year (or 1500 hours) and inspect it so I have a hard time putting an old impeller back in a pump. Especially when it's a pain in the ass to get to. That's like inspecting the duckbill valves on the sewage system and putting the old ones back if they are ok... no thanks.
 
Four Suns said:
Even though most pump manufacturers give a time period (or hours) to "inspect and replace worn parts" for the pump, many of them also state in the manual to remove the impeller if the boat is being winterized or sitting for a long time so it doesn't develop a set. Most people ignore that advice and just see the "every two years" part. ........
Click to expand...
You are correct and I am guilty of that - and my "set impeller" proves that. I too would replace the impeller if I pulled it out every year. My feeling is that I winterize by feeding water thru the outdrive (b3 using muffs) using antifreeze with rust inhibitors. After I fill the system, I don't want to empty all this fluid now by pulling the water pump hoses off. So my personal experience says just replace it every two years. Last year I only put 60 hours but decided to change it anyway. Just my opinion
 
I replace mine every year. This year I did the whole kit. By checking things every year, you can catch stuff before they fail, like o-rings or gaskets too. Don't want to risk the whole drive to save $$ on a few pieces of rubber.
 
Four Suns said:
You may want to ignore the idiotic "mine are only replaced when they fail" advice... I doubt that's in any manual.
Click to expand...
The pot head is as correct w/ this as w/ his other posted BS.

The Mercury FSM for my engine states: Task: "Seawater Pickup Pump - Disassemble And Inspect", Interval: "Whenever Insufficient Seawater Flow is Suspected. (If Operating Temperature Exceeds Normal Range.)

This fully comports with my unwaivering, consistent advice that the pot head mocks, "inspect raw water flow at startup".
 
Two to three years is a reasonable amount of service from a raw water pump. Most Mercruiser raw water pumps have a phenolic plastic body. When servicing the raw water pump, it's is important that both the impeller and the plastic body are replaced at the same time! Not replacing the body may result in degraded performance and premature impeller wear. The kit for rebuilding these pump properly retails for just under $100.

Best regards,
Frank
 
jmunro123 said:
I was reading a magazine about things you can fix before they break. One of the suggestions was to replace the impellers. however it did not say when. Our boat is a 2004 with about 140 hours on her. What is the suggested replacement time. The boat is in fresh water 6 months of the year.
Click to expand...

Change now. I pulled mine last week as the boats getting launched in two weeks. Only got the boat last year but not sure when they were changed before. Purchased the new ones before I even looked. One is easy to change, the other is a pain in the a**s. They both looked good but changed them anyways. Kept one for a spare. My cost for each was about $30.00 soooo, small price to pay for peace of mind. Beyond that, I'm not an expert on these things so what appears to me that looks good, may be ready to fail anytime. At least I feel confident now that should'nt be a problem I have this season. As I use my boat a lot, there are a bunch of other things you can be blindsided with even with proper maintainance checks so, take the guess work out of the impellers when you can. I will continue to change every year, may be overkill, but still a small price to pay. My 2 cents worth (1.74 cents U.S) .
 
I just had the port engine impeller replaced on my 6.2 liter this week and learned that my Smart Craft system will tell you the water pressure being generated. My new impeller is generating about 4.0 lbs of pressure at idle while my starboard engine is generating less than 2 lbs. (actually it drops below 1lb at times) Based on looking at the water flow coming out of the exhaust, I would have assumed that they are pumping equal volumes of water, but I would be wrong.

My boat is a 2006 with 90 hours. (I bought it the end of last season and don't know its history, but I have to assume that the impellers were original)

I'm planning on changing my starboard next. The only question is whether to do it myself or have the marina do it. I want to see what the bill is for the port engine before I make any decision. If the labor is less than $300 I will have them do it.
 
fc3 said:
Two to three years is a reasonable amount of service from a raw water pump. Most Mercruiser raw water pumps have a phenolic plastic body. When servicing the raw water pump, it's is important that both the impeller and the plastic body are replaced at the same time! Not replacing the body may result in degraded performance and premature impeller wear. The kit for rebuilding these pump properly retails for just under $100.

Best regards,
Frank
Click to expand...

I agree with this, however I have a twist. I'll replace the impeller every year and the housing every 3. I average 120-140 years a year and this is my first boat with the impeller in the external raw water pump(rather than in the Alpha I leg). I keep a spare impleller on board as well.
 
Hey guys, Just wanted to update you on this. The impellers were changed today and they were still all there but they were cracked and disformed. Good thing I checked this out. The mechanic said they were done and it was almost certain they would start to break apart this summer.

Thanks Again, good call to change them. That likely saved me a big repair bill or at least a lot of inconvience.
 
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