Used impeller has weak flow at idle, but fine at cruise / WOT???

[Fordiesel69]

I know I will be flamed for this question........but.....:facepalm:

I got a used 165HP outdrive complete, and the first thing I did was take the pump housing off and inspect. The impeller was in perfect shape and felt soft and nice. The housing and upper gasket was perfect so I reassembled and torqued. It works and cools except at slow-no-wake speeds....just a tiny amount of flow.

I have two known good used water pump kits I just changed, I wonder what part is causing the low flow as it all looked good.

 

[Brentathon]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

I would NEVER split a drive and look at an impeller without changing the impeller. They're only like $10. I'm always surprised when people do that.
Drive impellers should be considered a part like a gasket or O-ring....."consumable" parts.

 

[Fordiesel69]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

I understand your point 100%, but the drive case was FULL of 50% water / oil mix. The problem was no quad o-ring. I wanted to slap it together, put cheap gear lube in it and try it out. Good news is no water intrusion now that the quad ring was replaced, and no gear rust.

Problem is no marina local sells the impeller seperate, and I need to get it cooling for this weekend. I have a 1yr old impeller that has maybe 30 hrs on it. But I hate to swap it in if somthing else could be an issue and have it do the same thing. If we conclude that it is indeed just a fatigued impeller, I would be willing to try again and plan on ordering a new one on the internet. Like I said the gaskets, seperater plate, and housing looked excellent!!

I have replaced many impeller that were perfect. I feel the internet over stresses the whole yearly thing. 3-5 yrs in fresh water is more realistic. Brackish/saltwater, then yes each year.

 

[scipper77]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

I'm just curious how you checked the flow while cruising / WOT ? I check my flow on muffs in the driveway so I pretty muck can only see the flow at idle or slightly above./

Also, if the impeller fins are weak (bent over with a good set in them) I could see them not maintaining a good seal while pumping water.

 

[Brentathon]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Ohhh...with this additional info: ".... I need to get it cooling for this weekend....", then all bets are off for getting sound/proper advice.
Desperation changes the whole game, ya know? It comes down to opinion, at that point (i.e What would you do? or What should I do?)

 

[Don S]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

The problem was no quad o-ring. I wanted to slap it together, put cheap gear lube in it and try it out

That is normally done by doing a pressure test. Look up in the adults only sticky at the home made testers. Just running it in the water one time may not show a leak.

Problem is no marina local sells the impeller seperate,

That's a good thing, because you are going to need the gaskets as well as the impeller, or it will suck air when on plane and overheat.

I have replaced many impeller that were perfect. I feel the internet over stresses the whole yearly thing. 3-5 yrs in fresh water is more realistic. Brackish/saltwater, then yes each year.

I have customers bring in impellers all the time that they think are good, only because the vanes aren't cracked or missing.
Problem is, they miss the most important test. Do the vanes straighten out completely within 10 minutes. To many people don't understand how a rubber vane impeller works.
The vanes straightening out and bending over is what make it a pump. If the vanes will not straighten out at low speed it doesn't pump enough to cool the engine.

 

[paultjohnson]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Did you only run your boat once since you had taken it apart? Im asking cuz last year, after my my boat sat all winter. I started it in the drive on muffs, first start of the yr. My 143 deg stat let the engine get up to about 165. That never happens on my boat. I started it 2 days later, and the temp stayed at a perfect 140-145 like usual. [with same impeller] . It was like the rubber impeller just had to be worked a little bit, and the vanes became flexible again and did its job after that. I used the boat a few time without issue, temp stayed in the low 140s. Had to pull the drive a month later to replace lower shift cable. Then i replaced all the bellows, water hose, impeller, gaskets etc. As general maintenance. I had it apart and wanted to be safe then sorry. I dont understand, you have 2 good water pump kits???

 

[Fordiesel69]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Did you only run your boat once since you had taken it apart? Im asking cuz last year, after my my boat sat all winter. I started it in the drive on muffs, first start of the yr. My 143 deg stat let the engine get up to about 165. That never happens on my boat. I started it 2 days later, and the temp stayed at a perfect 140-145 like usual. [with same impeller] . It was like the rubber impeller just had to be worked a little bit, and the vanes became flexible again and did its job after that. I used the boat a few time without issue, temp stayed in the low 140s. Had to pull the drive a month later to replace lower shift cable. Then i replaced all the bellows, water hose, impeller, gaskets etc. As general maintenance. I had it apart and wanted to be safe then sorry. I dont understand, you have 2 good water pump kits???

I have 2 used genuine mercruiser water pump kits that are 1 season old. One was run very minimal maybe 30hrs at most, and the other maybe 50 hrs. So I could swap those in. I see your point now with the bend of the blades. Mine looked good and soft, but I bet the do not straighten back out and apply enough pressure to the housing.

I have ran it 4 times, and have simply not idled it. Just start and power up on plane and stay there. No overheating. I just shut it off when I bring it down to idle, of put in neutral and rev to 1700 RPM. That will give it enough flow.

 

[paultjohnson]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

I have 2 used genuine mercruiser water pump kits that are 1 season old. One was run very minimal maybe 30hrs at most, and the other maybe 50 hrs. So I could swap those in. I see your point now with the bend of the blades. Mine looked good and soft, but I bet the do not straighten back out and apply enough pressure to the housing.

I have ran it 4 times, and have simply not idled it. Just start and power up on plane and stay there. No overheating. I just shut it off when I bring it down to idle, of put in neutral and rev to 1700 RPM. That will give it enough flow.

Look at Dons post ..He gave you a great 'splanation and some pics. And unless your piggybank is REALLY REALLY empty. Get a NEW impeller. The rest of the kit is probable useable. Impellers issues are just too hard to diagnose,by looking at em, and so [relatively] inexpensive. Skip groceries for a day an go new.

 

[Fordiesel69]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Will report back after this weekend.

 

[HT32BSX115]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

The (Bravo) impeller below has about 20 hrs on it.........

 

[scipper77]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

The (Bravo) impeller below has about 20 hrs on it.........

20 hours over how many years? Or maybe it was run dry at some point? Sorry just trying to figure out why a 20 hour impeller would look like that/

 

[fossill]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Looks like that one was run dry by the way the edges are melted.

 

[Pete104]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Anti-freeze can do that.

 

[Fordiesel69]

Re: Used impeller has weak flow at idle, but fine at cruise / WOT???

Well it is fixed now. I was a moron, the impeller was soft alright, so soft it would not put hardly any pressure onto the housing. I could pull it out and put it in without any effort. The good "used" one I put in was literally like new and I could hardly get the housing on without the use of a little dish soap.