Just want to see what length of time the impeller on Volvo MD7A
Johnson water pump might last. I put a rebuilt one in it ten years
ago and it is still pumping what appears to be adequate water
amount. I have put about 470 hours on the engine in ten years.
I hear all the stories replace every year???? But it is working
and I am of a mind don t fix it....but I feel there must be some
wear and as to time frame and wear amount I would like input.
Thanks Jim
Sailonthesea@aol.com
Water pump impeller
Moderator: Jim Walsh
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Larry DeMers
Re: Water pump impeller
You run a risk of damage from a failed or partially failed impellor. Never mind the problem of recovering the lost paddles off the impellor. They will lodge in the cooling passages and partially block water flow. That itself could be a big expensive repair bill to clear them out, depending on where they lodge...but by the time you notice that the water has stopped flowing, you may have already warped your head due to overheating in localized areas.
This is foolish economy in my opinion. Do you change your oil every 100 hours or less? Hope so..well, changing the impellor every year or two is a darn good idea also. Now you don't put that much time on the engine..I believe you said 500 hours in 10 years, so ~50 hours a year. With that figure, I would expect that waiting even 3 years to change the impellor would be ok, provided that the water you run in is clear..not silt or sand filled, and you remove and inspect the impellor twice each year (look at it closely, physically bend each paddle back each way and inspect for *any* deformation, pits or cracking at the paddle root..replace it immediately if you see anything at all suspicious).
My practice is replace the $12 part (I use the Blue Nitrile Globe impellor, as they can run dry for quite some time, which makes them a tougher product than the competitiors..less likely to fail) every year to two years, and reserve the old one for a spare if it shows no wear at all. I would probably agree that in your case and probably mine also, changing every year may be a bit excessive. But it just depends on the hours of use and clarity of the water being pumped. If you are in silty water, that will wear the impellor far faster than up here in drinking water clear Superior. I suspect that is why some folks change out the impellors yearly. Their environment is tougher on the gear.
But certainly going 10 years on an impellor is asking for trouble.
Last hint. If you stow the boat for a period of time..like over winter, remove the impellor from the pump and store it away safely. The impellor, if not removed, will take a set to it's paddles from the nonuse, and will not recover from it, leaving one paddle bent back about 60 degrees all winter. When it runs with this condition, both chambers on either side of the deformed paddle will not pump water, which cuts your water output in half almost. At some point, that could cause hot spots to form in the engine, and that could cause warping or other problems.
Hope this helps.
Good Sailing!
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
demers@sgi.com
This is foolish economy in my opinion. Do you change your oil every 100 hours or less? Hope so..well, changing the impellor every year or two is a darn good idea also. Now you don't put that much time on the engine..I believe you said 500 hours in 10 years, so ~50 hours a year. With that figure, I would expect that waiting even 3 years to change the impellor would be ok, provided that the water you run in is clear..not silt or sand filled, and you remove and inspect the impellor twice each year (look at it closely, physically bend each paddle back each way and inspect for *any* deformation, pits or cracking at the paddle root..replace it immediately if you see anything at all suspicious).
My practice is replace the $12 part (I use the Blue Nitrile Globe impellor, as they can run dry for quite some time, which makes them a tougher product than the competitiors..less likely to fail) every year to two years, and reserve the old one for a spare if it shows no wear at all. I would probably agree that in your case and probably mine also, changing every year may be a bit excessive. But it just depends on the hours of use and clarity of the water being pumped. If you are in silty water, that will wear the impellor far faster than up here in drinking water clear Superior. I suspect that is why some folks change out the impellors yearly. Their environment is tougher on the gear.
But certainly going 10 years on an impellor is asking for trouble.
Last hint. If you stow the boat for a period of time..like over winter, remove the impellor from the pump and store it away safely. The impellor, if not removed, will take a set to it's paddles from the nonuse, and will not recover from it, leaving one paddle bent back about 60 degrees all winter. When it runs with this condition, both chambers on either side of the deformed paddle will not pump water, which cuts your water output in half almost. At some point, that could cause hot spots to form in the engine, and that could cause warping or other problems.
Hope this helps.
Good Sailing!
Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior
Jim Lewis wrote: Just want to see what length of time the impeller on Volvo MD7A
Johnson water pump might last. I put a rebuilt one in it ten years
ago and it is still pumping what appears to be adequate water
amount. I have put about 470 hours on the engine in ten years.
I hear all the stories replace every year???? But it is working
and I am of a mind don t fix it....but I feel there must be some
wear and as to time frame and wear amount I would like input.
Thanks Jim
demers@sgi.com
-
Ken Cave
Re: Water pump impeller
You probably do not have a raw water filter installed on your boat-which is even more concern in inspecting and installing a new inpeller every other year. I know, they are a bitch to get at-but it is necessary to inspect.
Also, check out your pump to see if you have any leakage there. If you see any, replace the pump pronto as the old ones have a tendancy to leak into the engine.
The new pumps are built almost bullet proof-and can be purchased darn near wholesale through Marelco in Seattle for about $140.00 delivered
Their phone number is 206 545 4224 and the part number is F35-B-9-1035157-3 pump and two clamps number 01-43238. It will take some modifications to install this pump as it is a little longer than the old pump but it is worth the trouble!
Hope this helps
Ken Cave CD28 #227
Anacortes, WA
bcave@whidbey.net
Also, check out your pump to see if you have any leakage there. If you see any, replace the pump pronto as the old ones have a tendancy to leak into the engine.
The new pumps are built almost bullet proof-and can be purchased darn near wholesale through Marelco in Seattle for about $140.00 delivered
Their phone number is 206 545 4224 and the part number is F35-B-9-1035157-3 pump and two clamps number 01-43238. It will take some modifications to install this pump as it is a little longer than the old pump but it is worth the trouble!
Hope this helps
Ken Cave CD28 #227
Anacortes, WA
bcave@whidbey.net