The Hull Truth - Boating and Fishing Forum

Go Back   The Hull Truth - Boating and Fishing Forum > BOATING FORUMS > The Boating Forum
Search

Notices

Random Quote: i jus took a reel nice dump
Reply
 
Thread Tools Search this Thread
Old 07-04-2011, 12:52 PM
  #1    
Senior MemberCaptains Club MemberPLEDGERPLEDGER
 
Join Date: Jan 2006
Location: Maui and SoCal
Posts: 7,106
Default Why do impellers look fine but not work well?

I've just done another water pump impeller change and as usual, the one coming out looks just fine, but the new one outperforms it. Why? I know the vanes are curved from being in the housing, but as soon as you put the new one in, they are curved too. But looking at the old impeller closely, I find nothing that would make me say "Oh, that's why", even when the new impeller is in the old housing.

I have found that the more often you use the boat, the less often you have to change impellers. I talked to a charter operator yesterday about how often he changes his on boats that are used daily and he said "Almost never. The lower units wear out before the impellers go bad." What am I missing? Does the rubber weaken from sitting but stay fresh if used constantly? That does not seem to make any sense.
__________________
Kern O.
kerno is offline   Reply With Quote
Old 07-04-2011, 12:59 PM
  #2    
Senior Member

 
Join Date: Mar 2003
Location: Quebec, Canada and Pirates Cove, OBX, NC
Posts: 19,248
Default

The rubbery in the impellor loses its 'memory' and soften ups and its effectiveness is reduced as it no longer seals tight when spinning at a high speed
__________________
.[________________________________




auguste is offline   Reply With Quote
 
Old 07-04-2011, 02:00 PM
  #3    
Admirals Club Captains Club Member
 
Join Date: Feb 2002
Location: Morehead City NC
Posts: 3,718
Default

They do last longer the more you use them. The average boaters puts less than 100 hrs a year so they sit for long periods of time in the bent position and lose their ability to pump enought to keep the motor cool.
Plus it's impossible to change offshore so it's just preventive maintenance
__________________

28 Enviboats Custom Cape Lookout Express
300 Suzuki Single- 50 MPH
parrott is offline   Reply With Quote
Old 07-04-2011, 03:14 PM
  #4    
Senior Member
 
Join Date: Feb 2005
Location: Bagdad, Florida
Posts: 257
Default

Kerno,

Next time you change an impeller, look at how it fits into the housing. Even though the housing the impeller fits into is round, the shaft and impeller do not fit directly in the center. There is an offset which means some of the impeller fins are compressed more than others. When the shaft is turning this gives the impeller fins sort of a squeege/paddling motion. When the motor is not running, some of the impeller fins stay compressed more than the others. If the motor sits for a long time, these over compressed fins tend to stay more bent than the others and they and loose their effectiveness. They may look okay but they no longer do the squeege thing even though they are going through the paddling motion.

Dennis
dmeswi is offline   Reply With Quote
Old 07-04-2011, 03:23 PM
  #5    
Senior MemberCaptains Club Member
 
Join Date: Jul 2005
Location: easley sc
Posts: 1,552
Default

so lets say your boat is going to sit for 6-8 months you could take the impeller out and let it sit uncompressed inside..

just a thought ..
ctoolman is offline   Reply With Quote
Old 07-04-2011, 03:26 PM
  #6    
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Dec 2001
Location: Upstate SC, USA
Posts: 8,546
Default

Check your cam plate. If it's old and worn, it will affect how well the impeller works.
__________________

1988 Black Watch 30 Express
Wolakrab is offline   Reply With Quote
Old 07-04-2011, 03:30 PM
  #7    
Senior Member
 
Join Date: Apr 2009
Posts: 1,708
Default

Older impellers are fatigued. At speed, impeller blades do not open fully. this decreases the volume of water the vanes can deliver to the cam, hence lower volume.

I used the blue Barco Blue impellers once. Softer, easier to replace, but softer vanes do not pump as much. Great spares though.
54bullwinkle is offline   Reply With Quote
Old 07-04-2011, 05:08 PM
  #8    
Senior MemberCaptains Club Member
 
Join Date: Feb 2002
Location: Orange Park, FL
Posts: 973
Default

Impellers go bad due to lack of use and curve memory sets in. My engines are ran every week for at least 5 minutes each on the muffs, never less. I change my impellers every 2-3 years only because I'm told to. The old ones come out looking brand new, no curves. Been doing this for close to 20 years. Run the motors weekly and you will see a lot fewer problems.
__________________
2005 Caravelle 280 CC, Twin Suzuki 175's
Shel is offline   Reply With Quote
Old 07-05-2011, 01:51 AM
  #9    
Senior Member
 
Join Date: May 2011
Posts: 582
Default

Quote:
Originally Posted by dmeswi View Post
Kerno,

Next time you change an impeller, look at how it fits into the housing. Even though the housing the impeller fits into is round, the shaft and impeller do not fit directly in the center. There is an offset which means some of the impeller fins are compressed more than others. When the shaft is turning this gives the impeller fins sort of a squeege/paddling motion. When the motor is not running, some of the impeller fins stay compressed more than the others. If the motor sits for a long time, these over compressed fins tend to stay more bent than the others and they and loose their effectiveness. They may look okay but they no longer do the squeege thing even though they are going through the paddling motion.

Dennis
+1
puppy is offline   Reply With Quote
Old 07-05-2011, 05:16 AM
  #10    
Senior Member
 
Join Date: Jan 2006
Location: Sunny florida
Posts: 10,861
Default

Interesting observation and explanations.

Makes sense though. When normally soft parts get stiff, they don't work as well.

(WAIT a minute..THAT'S not correct either....)
billinstuart is offline   Reply With Quote
Old 07-05-2011, 05:23 AM
  #11    
Admirals Club
 
Join Date: Jan 2009
Location: Iowa
Posts: 7,692
Default

Quote:
Originally Posted by billinstuart View Post
Interesting observation and explanations.

Makes sense though. When normally soft parts get stiff, they don't work as well.

(WAIT a minute..THAT'S not correct either....)
__________________
Lund 1850 Tyee
Mariner 150 HP
Lowrance electronics
MinnKota trolling motor
Best part ITS PAID FOR
davidkuhlmann is offline   Reply With Quote
Old 07-05-2011, 06:13 AM
  #12    
Senior Member
 
Join Date: Sep 2010
Location: Richmond/Topping VA
Posts: 275
Default

Quote:
Originally Posted by billinstuart View Post
Interesting observation and explanations.

Makes sense though. When normally soft parts get stiff, they don't work as well.

(WAIT a minute..THAT'S not correct either....)
Hmmm...depends on the model year of the parts in question.
Uncle John is offline   Reply With Quote
 
 
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 



©2009 TheHullTruth.com

Powered by vBulletin® Version 3.7.6
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.2.0