Changed impeller but won't pee at full throttle

[cajunman83]

I just got finished changing the water pump on my 1999 25 Mercury, which included the impeller, housing, faceplate, gaskets and seals and it pumps water but not good. I've checked the tell tale for obstruction and there is none. I've flushed the system with the water hose from the copper water pipe and got it to pee and then did the same flushing from the tell tale and had water running out the copper pipe.

It pumps at idle but takes about 5-10 seconds before it starts peeing. I can run about 1/2 throttle and it'll do fine too. The real problem is when I'm all out. After about 45 seconds or so of running full throttle the pump seems to sputter out and quit. Lots of steam is coming out, like the water is being boiled. When I bring it down to idle again it takes about 5 seconds for it to start peeing again. And the water is SCALDING hot!

I have no idea what else to do. (besides succumbing and bringing it to the shop) The motor doesn't have a thermostat so that's not the issue. I made sure the keyway was in correctly too. I turned the drive shaft clockwise to assure proper impeller installation. Made sure nothing is blocking the screen on the foot. I made sure to have good a good connection between the water pump and the bottom of the motor as well as to the water pump. And now I'm STUMPED!!

 

[1nebel0]

Re: Changed impeller but won't pee at full throttle

I going for the long shot here as everything you have written, makes where it should work....I have found that if you don't use a factory Merc impeller that sometimes they don't work right. Don't ask me to explain it because I can't. All I can think is the hub is spun and stops working under a heavy load...try a new impeller..you are looking at $20 and change versus $100 an hour..Make sure you have a gasket under the metal plate and on top of it...Everything you listed is correct...please post if you resolve the issue as we all will learn from your situation....Steve

 

[cr2k]

Re: Changed impeller but won't pee at full throttle

Pull the intake screens on the drive and see if there is anything in there.

 

[Maxz695]

Re: Changed impeller but won't pee at full throttle

Was your last impeller in one piece when you removed it?

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

1nebel0: The water pump kit was purchased from my local Mercury dealer at their parts counter and came with the gasket, face plate and new impeller which I replaced.

cr2k: I've checked that also. That was one of the very first thing I checked.

Maxz: Yes all one piece. It looked fine except for the fact that the veins had a little curve to them. It also had a date stamp on the rubber (1999) the same year as my motor.

 

[Maxz695]

Re: Changed impeller but won't pee at full throttle

View attachment 92213View attachment 92214View attachment 92215View attachment 92216I don,t know how long you owned your engine and if the previous owner may have had an eploded impeller. When was the last time you knew it to work correctly? This I posted on another post this morning maybe it can give you insight RE: Particles from a previously broken impeller can be floating around inside your engine allowing water to flow at times and block passages at other times. They can be lodged and unknow and unrecognizable and then suddenly come free and block passages agin. Flushing and backflushing may help, but even after I did this and thought I had it. I was waiting on new waterpump a base, and I had a powerhead gasket set so I deciede what the heck why not do all the gaskets. I after lifting the powerhead found a peice of old impller and something eles not sure. I also found a piece in the exhaust port cover.

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

It was working correctly when I bought it and when until about 2 weeks ago when it just seemed to quit. I had ran through some sand and figured that's what did it in. The last step seems to be to tear it apart as shown in the pictures above. How hard of a job is this and what parts would I need?

 

[Big flop]

Re: Changed impeller but won't pee at full throttle

Are you sure there's no thermostat?
Can you post serial number?

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

Positive. The Mercury shop insisted there was one but it seems that there were two head covers for that motor and mine doesn't have one. I bought the stat after giving him the S/N and him insisting there was one but sure enough when I got home there wasn't. I just have a threaded hole coming out of the cover that goes to a plastic 90 elbow that connects to my rubber telltale hose.

0G928965

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

I know the plug looks bad, and I plan on changing it as soon as this pumping issue is solved.

 

[Big flop]

Re: Changed impeller but won't pee at full throttle

And no thermostat in the top of the block
between the coils and flywheel?

 

[1nebel0]

Re: Changed impeller but won't pee at full throttle

I am not shifting my bet on Maxz 695...Pull the power head as you need to eliminate the possibility of what happened to him......can't wait for you to figure it out as this is a good lesson for everyone..

 

[Big flop]

Re: Changed impeller but won't pee at full throttle

I see that water cover with no thermostat.
it is sounding like internal restriction.
it's not to hard coming apart,I would
recommend OEM service manual.
And you'll figure your parts list as you go.
Take lots of pictures for later reference
Was the sealing surface under base plate gasket
in good shape? If it's pitted it will suck air.
Is anything mounted on the transom in front
of the lower unit? A transducer or speedo pickup,
Anything that will put air in cooling system?

 

[j_martin]

Re: Changed impeller but won't pee at full throttle

It's verry unlikely for a paddle pump to pump well at slow speeds, and fail at higher speeds. Also, good water flow at slow speeds pretty well rules out an obstruction.

The steam is a clue. Either it is failing to get water, ie there's something that's entraining air in the wake being picked up by the pump, or combustion gasses are getting into the water jacker, ie bad head gasket, cracked cylinder, etc.

just my 02
John

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

Bigflop: I'll check on that stat but I'm pretty sure, no. Also, if it's sucking air, logically when I kill the motor it would water would leak where air was coming in, correct? Because there's not water that I can tell. Only thing it could be is a minuscule break in the seal not big enough to let water out.

J_martin: What do you mean something that's entraining air in the wake being picked up by the pump? Or did you mean entering? Also I hope it isn't a cracked cylinder cus she purrs like a kitten. Great power and idles as long as I want it to and never dies. A cracked cylinder would mean water entering, right? A bad head gasket would cause water to get in the cylinder as well, correct? Thus, I would see rust deposits in the chamber, right? Just trying to rule out every possible thing.

I went up to the Merc shop yesterday and they couldn't give me any help....of course cus they want my business. They did, however, try and sell me a brand new 4-stroke..haha

 

[Big flop]

Re: Changed impeller but won't pee at full throttle

If this a problem from air getting into the
cooling it would be coming from down low.
If the gasket under the the plate the impeller is on
was not sealed good (pitted housing) it would suck air and
Or exhaust, If something is mounted on the transom in
front of the lower making air bubbles into cooling water.
If the water that is cooling the motor has air in it
it can't pull the heat out.
I would check this out and if it all looks good
Then you have to think about top end restriction.

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

Big Flop: I checked what you suggested and all seems fine.

I removed the water jacket cover and exhaust manifold this evening and found a lot of buildup on the exhaust ports. There was also some sand blocking clogged in water port hold as well as a tiny pebble blocking another. There were some other ports available for some water flow however. I'll get the gaskets tomorrow and check for better flow. Hopefully this solves my problem!!

 

[1nebel0]

Re: Changed impeller but won't pee at full throttle

I think he is about to tell us that he got it....this will be a good one for the books...Thanks cajunman for posting...

 

[cajunman83]

Re: Changed impeller but won't pee at full throttle

I sure as heck hope so....there's not too much else I can change!