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1985 25hp Mariner cuts out after approx 5 minutes

billwww

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"I just had my carb rebuilt, w

"I just had my carb rebuilt, with a new float and I also replaced a stuck-open thermostat. Previously, the engine would over heat and was hard to start. Starting in now no problem. The repair shop showed no obstruction in the cooling. But, after I got the engine back from the shop and put back on the boat, have noticed that after 5-10 minutes, steam starts to come from the lower unit. The previous owner had the water pump replaced on 2005, if that means anything. Also noticed that when the engine cuts out, the bulb in the fuel line gets soft. When I pump it up while the engine is running, the engine starts to run smoother, but only for a few seconds, until it begins to stop again. Have noticed when I replaced the thermostat, the small chamber that the stat sits in does not seen to have any openings under the stat. Is the water supposed to run thru the stat? I need my motor before winter comes.
HELP"
 
"Bill, the waterpump impeller

"Bill, the waterpump impeller is due for a change again and pumping the bulb and having it "come back to life" indicates a bad fuel pump.."
 
"Graham, thanks for the infor

"Graham, thanks for the information. I know how to remove the fuel pump, but is it a big job to repair the waterpump? I know the lower unit must be removed, is there a step-by-step instruction available somewhere?"
 
"Bill pulling the lower and re

"Bill pulling the lower and replacing an impeller etc is a fairly easy job. But as you elude to, it is a series of steps.

It really is best to grab a Seloc's manual for your model. 35 bucks for the book can save hundreds in case of an "oops"..."
 
"Thank you Graham for all your

"Thank you Graham for all your help.
I replaced the water pump impeller, and found that the old one looked as good as the new one. I replaced it anyway. The engine starts quickly, runs well at idle, slow and medium. The water flow from all ports looks good when running slow and medium, but when I open up full, the water spout from the bottom of the engine housing, reduces to a dribble and then turns to steam. Also, steam comes from the exhaust.
If I reduce speed to slow or idle, the water stream returns to normal and the steaming stops.
When steaming, the engine does not run rough, but I am afraid of what could happen.
What do you think?"
 
"Bill, that definately indicat

"Bill, that definately indicates a problem. The steam means it isn't getting enough water to the powerhead and it's overheating.

Since the impeller was in good shape the problem definately lies elsewhere.

What was the condition of the water cover gasket? the seal at the top of the water cover where the water tube enters? possibly a hole in the water tube itself (have seen it) - seal where the water tube enters the exhaust plate up near the powerhead could be shot.

It sounds like somewhere between the impeller and the powerhead you are "leaking water". I suspect that when the impeller is turning at lower rpm the leak is not severe enough to impede the water getting where it needs to go but as soon as you crank it up you are losing enough that it can no longer cool things down.

You have done the easy fix, which was the way to go, unfortunately it wasn't the problem. You are most likely going to have to pull the powerhead and separate the exhuast housing (leg) to ensure everything is intact.."
 
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