Water flow slows and almost stops

[jwstandiford]

Hellow all. I have seached and searched for a thread that will help me with my problem and though I have found lots of helpfull information I am still experiencing the same problem.

First off, the motor I have is a 1978, Evinrude 25hp, Model # 25852.

I inherited this motor after my father in law passed and I know that it had been in storage for at least 7 years as they no longer owned a boat. From the first test I noticed this problem and have yet to get it corrected.

The problem: The motor starts and runs great with a good strong stream of water comming from the tel-tail. After 5-10 minutes of running at idle (test running in a barrel) the flow of water gets weak and seems like it will stop flowing completely if let run. As soon as the flow starts to dwindle the head starts to heat up rapidly so I shut it down.

The impeller seemed to be OK but I replaced it anyway. The stainless plate on the bottom of the pump showed some wear but I could not find a replacment. The t-stat was bad so that and the cover gasket were replaced. I blew 100psi air backwards and forwards throught the system while I had it appart and it seemed that the flow was not restricted. I replaced the hose coming from the head to the tel-tail becase it seemed kinked and cleaned out the tel-tail itself. After re-assembling and testing I recived the same results. I then removed the t-stat and tested again with the same results.

Any input would be appreciated.
Thanks,
JS

 

[JUSTINTIME]

Re: Water flow slows and almost stops

did u replace the impller housing?

 

[tashasdaddy]

Re: Water flow slows and almost stops

did you install the impeller with the vanes leaning the correct way?

 

[jwstandiford]

Re: Water flow slows and almost stops

I did not replace the impeller housing as it did not have any visible wear marks, and the impeller is installed with the vanes going the direction as specified in my manual. I figured that either of these would cause the water pump to not pump at all or pump with little pressure at all times. My issue is that I get good flow for several minutes and then as the motor warms up the flow weakens.

I had another of these motors (same model actually) that I purchesed with a friend and it had cooling system problems initially which ended up being a blockage in the block somewhere. In that case the eventual fix was blowing air through the system. The experience with that cooling system problem is how I remembered to check/ replace the parts that I did. But with that motor the blockage prevented the pump from moving very much water at all from the begining.

I just can not figure out what could be changing as the motor runs to cause it to lose pressure and flow in the cooling system as it warms up. Some times it will run for almost 10 min. before it starts to lose flow.

 

[Broken1]

Re: Water flow slows and almost stops

I had an old Merc once that the impeller turned on the hub. I guess the friction caused the rubber to loosen on the hub and after it had enough, the rubber started spinning on the hub.

 

[freddyray21]

Re: Water flow slows and almost stops

correct me if I am wrong, but until the thermostat opens the water coming out of the tell tale is from the bypass. Once the thermostat opens the water then goes through the head and the passageways. If those are blocked then the water would not go through. I would pull the thermostat and make sure I had water not just air through all the passageways. Insects including wasps have been known to crawl up the telltales and build nests in the passageways. Just a thought.

 

[jwstandiford]

Re: Water flow slows and almost stops

I get the same result with the t-stat out. It will run fine for several minutes with a strong flow, but then the flow starts to weaken and the head starts to heat up.

 

[mikesea]

Re: Water flow slows and almost stops

I agree with previous poster,be sure engine continues to pump water.Does your test tank have enough water to submerge the waterpump,it does sound as though the pump is becoming airbound,or for some reason just not pumping water,odd that it stops after a few minutes,,remove the t-stat cover after it stops pumping to see if water is getting to that point,Ive seen when there is a plugged system the tell tale will blow steam,you get a waterlock and the water heats to steam.If you lose the water to the t'stat,I'd look at the pump again,you might need the plate replaced

 

[freddyray21]

Re: Water flow slows and almost stops

If it pumps good initially then it is pumping okay. Could be if you are running the prop in the tank you are causing an air pocket in the tank where it's sucking air instead of water. I would still check all the passageways to see if they are clear.