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Another water pump question

7/31/18 @ 10:31 AM
User since 5/8/02

I have a 1994 Mariner Magnum 40HP tiller.

I put a new impeller in it in early 2017, old one was gone.

When I am running at idle or slower speeds, I get a good healthy stream of water.....about 97% of the time.

Sometimes the stream will stop for a few seconds, then start right back up again. It's hard to tell if I am getting a good stream of water at full speed, since there is so much splashing around that area, I can't tell.

Is this normal for the stream out the peephole to stop once in a while, then start back up again ?

I make sure that the tube from the top of the engine is clear and it seems to be, I've cleaned it out a number of times.

The water coming out is very, very HOT, which I assumed it would be.

Otherwise, it runs out good. 

Could the impeller be going bad that quick ?

5/12/19 @ 4:43 PM
User since 5/8/02

Okay, this will be my final post on this subject since we have found and solved the problem. Maybe it will help other people.

After a mechanic literally tore down the motor after finding very small pieces of impeller in the water cooling jackets, he also found a bunch of mud, dirt in the jacket, mostly in the lower jacket where you needed to pull the top portion of the motor off. 

Had the motor out today and this thing pees like crazy now. The water is barely warm to the touch where before you could not hold your hand under the stream because it would scald you. I've had this motor going on 3 seasons now and I don't think it has ever operated like this before, apparently the previous owner either didn't know it or just didn't care.

So, if anybody has any problems with overheating or not peeing like it should , that may be an option. Not a cheap option, but sometimes you have to do it to resolve in issue.

5/6/19 @ 3:14 PM
User since 6/1/09

I fish Big Muskego all the time Have-a 50ETec. No problem with mud ,just have to watch certain areas with the weeds. Trim up and run to certain areas and then use trolling motor.When I had the 50 Merc.I carried a 12in. Length of #12 wire and used it to clean out the discharge pee hole once in awhile because it would get clogged with slime once and awhile.ETechas a bigger discharge hole and no problems!

5/6/19 @ 12:23 PM
User since 5/8/02


The impeller is the thing that I can and will do when it needs it, however this was a little more involved and required a knowledge of outboard motors more than I have. I needed to get this fixed sooner than later so I don't have any more issues in the immediate future. 

5/6/19 @ 12:09 PM
Ed Franko
User since 5/6/15

I would have it checked out or replace it yourself as a  impeller is much cheaper that a motor rebuild.

Big Ed’s Guide Service
(573) 692-6710
5/6/19 @ 11:11 AM
User since 5/8/02


I had the motor to a guy you is in the process of fixing my situation.

He tore the whole thing down and found some very small pieces of the impeller in the cooling jacket, but mainly he said there was mud and dirt in the cooling system.

Now I do fish Big Muskego quite often, but I didn't think that running thru that water would so this.  He wasn't sure of how long it would take to get that stuff in the cooling system. He literally took the head off to get at the bottom cooling jacket and got that all cleaned out.

My next question is does anyone who fishes waters like Big Muskego ever have this problem periodically ?

9/27/18 @ 3:10 PM
User since 12/26/10

I had that same motor years ago,in 45 HP form.Any interruptions in pee stream indicate a floating obstruction in cooling system.That motor should pee steady,and should be able to hold hand over stream for a good time.

The only outboard that water came out hot,was a 25 HP Mercury.That model has the overboard indicator after the thermostat,and you could see the thermostat open and close by the strength of pee stream.

It would be a great idea to replace all the water jacket gaskets on that motor,they are know to leak.Also check the parts for warping.If the water cover jacket on the cylinder head says"power dome combustion chamber",that is a design that goes back to the 50s.One of the reasons OMC used to tout their lost foam casting process.Less gaskets to leak.

9/27/18 @ 12:44 PM
User since 5/8/02


How big were the pieces of the impeller that you pulled out of your motor ?

I'm going to have a guy pull my water cooling jacket off and find out what's happening.

9/4/18 @ 3:02 PM
User since 6/9/06

I'd say you need to remove the cylinder head(s) and look for the old impeller pieces in the water jacket passages.

You'll need new head gasket(s), torque spec and bolt pattern tightening sequence.

Good luck.


9/4/18 @ 2:41 PM
User since 5/11/18

I'd be willing to bet you still have peices of the old water pump in the cylinder head cooling passages. This is what happened on my 40hp Yamaha, pulled the cooling jacket off and found tons of rubber impeller peices stuck should always have a steady stream no spray.

9/4/18 @ 12:47 PM
User since 5/8/02

So I have had the rebuilt parts out for a number of times since I replaced the impeller and a few other gaskets, and it really did not make much of a difference. There does seem to be more water coming out of the p-hole than before, but at high wide open throttle, it is more of a heavy spray than a stream of water. Up to about 25 mph, it is a steady stream, after that up to about 31 mph, it is a heavy spray. After running for a while, the water is still extremely hot, I would not want to keep my hand in that stream for more than 5 seconds. 

When I replaced everything, I even backflushed the water jacket by pushing water thru the p-hole until it came out of the water tube that goes up into the power head.  

I have not gotten the high temp warning since replacing all of the gaskets however. I don't know if there is anything else I can do on this. I will just have to watch it. 

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