difference between a impeller and water pump?

[IneedAnewScreenName9886691]

is a impeller (sp?) and a water pump the same item on a 89 merc 175 :-?

Thank you for in advance!  

[ernel]

The impeller is the main part of the water pump. It is what picks up and moves the water into the motor.

[Ben]

Yes.

In laymens terms, the impeller is the rubber thingamajig inside the water pump that moves the water.

The water pump is the complete assembly.  Unless the gaskets, O-rings, etc are broken or the housing is damaged, you can usually just replace the impeller.   I usually replace the entire assy the first time and impeller the second, then the entire assemble again the next.  However, I also replace mine every two years and grease the driveshaft spline.

[IneedAnewScreenName9886691]

Thanks guys!

When I bought this boat the old owner told me he replaced the impeller in the '89 Merc two years ago. My mechanic when I told him I got an 89' Merc said "you gotta replace those water pumps every two years for preventitive reasons" he said they were notorios for going out.

[RatONaStick]

Oops, too slow.

[Glenn]

hydrillagorilla2, your mechanic shoots from the hip.  He's dead on right.  Stick with him.  He's good people.

[IneedAnewScreenName9886691]

Thanks Glenn!  It has been hard finding one I like.  This guy has been working on my boat for a year now and I think he is good as well.  

Thanks for the vote of confidence, cause when it comes to these things- you never know.  

[jb_from_texas]

if your motor is running fine and the water outlet on the motor is expelling the water as it always has/should, can there still be a problem in the assembly?

Ben, has there been times you swapped out the impeller for preventative reasons only and realized there was a problem with it, without any symptoms to indicate as such?

[Ben]

Strickly as preventive maintenance, I also change my LU lube twice a year, but I also fish all 12 months of the year.  First thing I do on any used motor I buy before putting it in the water is change the LU lube and the water pump.  A $30 impeller or a $50 kit every couple of years is a hellava lot cheaper than a fried powerhead or a spoiled fishing trip.   A also like to pull my LU and grease the drive shaft spline so why not just do both at the same time.

I've seem too many people run theirs untl the water pump quits (that can be years and years) and then can't get the drive shaft out of the crank where it has rusted in there.  Another problem with running one till it quits is when it does quit, it usually comes appart, sending chunks of rubber up into the block to stop up water passages causing it to run hot after putting new pump in or creating hot spots.

The people I really love most though are those that always crank their motor at the ramp and rev it up a couple of times before launching the boat, I guess just to make sure it's going to crank after they launch it.  Doing that fries the tee total crap out of a water pump.  Only takes a few seconds for that impeller running dry like that to make things nice and hot in there.

[IneedAnewScreenName9886691]

Ben,  Thank you again for bestowing your wisdom upon us.  You truly have been a great resource for me getting to know bass boats.  

Best regards,

Hydrilla

[jb_from_texas]

yes, thanks Ben.  i asked the questions so i would know, if anything, what to look for (other than the motor not expelling water) in between swaps.  And also what to look for once you pull the old one out, showing evidence of potential problems down the line.

[Ben]

Not expelling water out the pee tube is not really an indication the pump is not working. Dirt dobbers love ready made holes and those pee tubes make good nest. If they are a problem where you live keep a nail or something in the hole. As for visual indications, that's what water pressure guages are for, I don't run without one. Well, except for my 4hp merc, 9.9 Johnson and 25hp Merc tiller motors. If the motor has a steering wheel or stick connected, it has a water pressure guage and Tach. Two manditory items in my boats.

I've never known one to go bad in two years unless, that why I swap them that often. If you run in a lot of shallow water where it sucking sand and silt into the motor, that will eat one up pretty quick and cranking one up dry will fry one in a heartbeat but other than that, they usually last the two years. As for what to look for, just not much too the things, and if you get the kit, they usually have everything needed to make it like new again unless the housing itself is damaged in some way.

As for what a bad pump looks like that's still pumping and hasn't come apart year, the blades will have dryrot cracks in them if you bend them a little extra, or the tips will be rubbed/melted off or made real thin from wear or heat. The blades are also no longer pliable, they get so hard they keep almost the their full bend when you take them out of the housing. Plastic housings you want to check for being melted and cranks.

[joeuknow]

I have a 2001 Mercruiser 5.0 and there's apparently a fresh water or raw water pump on the engine block that's driven by the serpentine belt.  Is there also an impeller in the Alpha One leg?  If so, what's the difference between an impeller in the leg and a fresh or raw water pump on the engine block??

[WRB]

Inboard auto engine vs outboard boat engine with a lower unit submerged in the water. 

Tom

[TnRiver46]

Impeller is a rubber spinning wheel (or so I thought). Then again we’ve always used the terms interchangeably when referring to outboards 

[Krux5506]

On 6/8/2006 at 7:04 PM, Ben said:

Not expelling water out the pee tube is not really an indication the pump is not working. Dirt dobbers love ready made holes and those pee tubes make good nest. If they are a problem where you live keep a nail or something in the hole.

Ugh...Had that issue this year. Fired up my motor and had it running for a minute or two before I realized it wasn't peeing water out. Quickly shut off and tried to figure it out...Finally realized the tube was closed shut with dirt. Cleaned it out with a little file tip and it worked fine. Then later noticed my bilge outlet tube was plugged too! By the way that dirt smells absolutely horrible lol

[J Francho]

15 years running !!! 

[king fisher]

Pictures of a new impeller for 70 horse Yamaha outboard, and one I just replaced on the water pump of a C32 Acert Caterpillar Diesel marine engine.  I replace both every two years or sooner, depending on engine hours.  The CAT impeller costs $700, a complete pump runs around $4000.  Hope this makes outboard owners feel better about preventive water pump expenses.