Merc 7.5 Cooling Problem

n26panache

Cadet
Joined
Sep 2, 2009
Messages
7
Start of the season and there's no water running out of the outboard. It's a 1984 Merc. 7.5 HP two-stroke

Searching these forums I've found plenty of replies to this same problem which suggest replacing the impeller. That was the first thing I thought of as well, so I already did that - though the old one looked like it was in decent shape, actually.

I've run water back through each section of the system. So there doesn't seem to be any blockages.

I've tried flipping the blades of the impeller both ways.

The best I can get is eventually a tiny bit of water spitting out of the little pee hole and lots of exhaust smoke coming out of there as well (since I've had it, the motor has always run pretty smokey generally).

One fellow boater mentioned to me on the way home that maybe it's just the thermostat doing it's job - it's about 5 degrees today and the water's still pretty freezing, so maybe no water needs to run? I just never remember seeing the motor running without water coming out (and is there even a thermostat on these things anyway??).

My only other idea is that because I only ran water "down" the system from the top, maybe there's a hole in the tube and it's preventing the water from coming "up". Tomorrow I'll try blowing water "up" (i.e. the proper way) and see what happens.

Any other thoughts?
 
Last edited:

Wingedwheel

Lieutenant Junior Grade
Joined
Jun 16, 2009
Messages
1,071
Re: Merc 7.5 Cooling Problem

I'm having the same problem, with the same outboard. I did everything exactly as you have done.My cup and plate looked fine Did you put the engine in the lake and test or just a tank? I'm wondering how deep in water this engine needs to be to get pick-up. I'm not a novice to outboard repair, but this is baffling.
 

Wingedwheel

Lieutenant Junior Grade
Joined
Jun 16, 2009
Messages
1,071
Re: Merc 7.5 Cooling Problem

I'm just wondering if you had it deep enough in your test tank or did you actually drop it in the water?
 
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