[wichi]

I have a Mercury 25hp efi fourstroke thats having water pressure issues. Replaced water pump, blew air in peehole and doesnt seem to have any obstruction. After replacing water pump psi started great went about 300 yards and same problems started occuring. The pressure just dropped to 0 with little water coming out. It seems to work off and on. Sometimes great pressure then for what seems like no reason just quits. It was running fine in idle yesterday after blowing compressed air through the pee hole, then i trimmed motor down and all of a sudden nothing. Water pressure dropped. Forced water through intake while lower housing was off and water came out fine. Removed houses last night and forced air through system, and again no obstruction. Could this be a thermestat issue? Local dealer said no, to replace pump. When I took it apart the old one was in good shape but went ahead and replaced with new. Any Help or ideas would be greatly appreciated. p.s. The motor is only two years old.
thanks

[wichi]

I figured out the problem. After removing thermostat and forcing water through system still no signs of blockage, sand or build up. I removed lower housing unit and forced water through lower unit. When doing so I discovered a pin sized hole in the lower water pump housing. When high water pressure was applied it shot a stream of water out. How this pin hole developed on a two year old motor I have no idea, but finding it saved me hundreds of dollars and time lost at shop. Hopefully this will never happen to anyone, but if your losing water pressure when replacing water pump take a look it will save you alot of headaches down the road.