1400 merc (78) water pressure in question

tramp666

Seaman Apprentice
Joined
Apr 15, 2007
Messages
47
Hi all, I finally have this thing running pretty good. After a few rounds with the carbs coming off and on I finally got the floats right. Thanks to you guys and the Boat Doctor, and Paul in Panama City Fl. Great advice but they refuse to touch it. So now I'm becoming somewhat of an x-pert with there help or lack of help depending how you look at it. Anyway... to the latest issue...
the water pump seems to pump more air than water at higher RPMs so I took the foot off inspected the impeller (new last year) and all was good so back together for another go around the lake. At low speed it pumps great and I'm confident it is cooling the power head. But at higher RPMs it seems to not pump as much water and I'm concerned that it may hurt the motor by not getting enough water to do the job. There is no alarm, no temp gauge, no pressure gauge just me guessing if it's going to melt down at any minute. So I go slow. At least until someone can shine some light on this new (to me) delema. Could this be a product of cavitation not letting the foot get enough water to pump or am I way off?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,074
Re: 1400 merc (78) water pressure in question

If the engine does not rev up and ventilate, it would be unusual for the water intakes to be affected.

The inline motors never had any real water pressure, but at high speed you should have 10-15PSI. Can you install a gauge? How do you know it is pumping air?

BTW - if it is pumping air the engine will seize very quickly...
 

tramp666

Seaman Apprentice
Joined
Apr 15, 2007
Messages
47
Re: 1400 merc (78) water pressure in question

When I say it's pumping air... I mean it looks like a mix of water and air running at lets say 1/2 to 3/4 throttle. I may be just paranoid. At low speed the water coming out is hot to touch and a solid stream. At speed it is hot to almost "steam like" and I'm concerned it's not enough to cool the power head. Now I've been running it for 2 years and it hasn't detonated yet. I'm just trying to make it right and reliable for my own piece of mind. If I was to put a pressure gauge on it were would it go?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,074
Re: 1400 merc (78) water pressure in question

The cooling water should never get that hot. You have a definite problem. It sounds like it is time to drop the gearcase, replace the impeller and see if that helps. If not you need to find the water jacket restrictions. Maybe you can detect hot spots with your hands on the block. At idle, the motor should run cool with the water no more than lukewarm. It wil be warmer at cruising speed, but never any steam.
 
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