96 Merc 125 outboard

[charlie2]

My Dad owns a 1996/97 Cajun with the Merc 125. For several years now he has had a problem with the cooling alarm. I had a red light installed as he cannot hear the alarm. When the motor is at full throttle for more than a few minutes the alarm goes off. In all other operating conditions it's fine. It has good water flow and pressure. We have been told that the motor needs some disassembly to have the water passages cleaned. Is there a way to flush this motor and is the temp sensor a possible fault?

 

[Barnacle_Bill]

Re: 96 Merc 125 outboard

Sounds like a bad popit valve. Has it been replaced?

 

[Texasmark]

Re: 96 Merc 125 outboard

Pop the cover and look at powerhead from the rear. Upper left corner of rear of engine on the water jacket cover is a cover with a small diameter top portion, a straight portion and a larger diameter portion on the bottom. It is held in place with 6-8 screws.

Under that cover is the t-stat and the poppet valve. While you have the cover off to inspect/replace them, you can answer your question about how dirty your water passages are and whether you think they need cleaning.

I just answered a similar question a couple of days ago and had more things to do while you are on the subject. Might look it up in this section of the site.

Mark

 

[charlie2]

Re: 96 Merc 125 outboard

Thanxs for the information, my Dad has had work done on this motor in the past with no mention of a poppet valve. i am a automotive mechanic and do not have much experience with marine motors. In viewing some of this forum I now understand how this cooling system works. I think you may have nailed the problem and will let you know how we make out with it. "Happy NEW YEAR" Charlie

 

[Texasmark]

Re: 96 Merc 125 outboard

The poppet gets pushed off it's seat with water pressure and opens a large non-temp controlled passage in the powerhead's cooling system. Since it is supposed to activate at around 2500 rpm's and water pressure is around 6 psig at idle and 12 roughly at full throttle, somewhere between those numbers is the design goal. Biggest problem with them that I could imagine would be that the valve is stuck to the housing and requires more than that pressure to unseat. This could be do to marine environmental contamination. Possibly a good cleaning with a tooth brush and mild soap and water is all that's required.

On the other side of the coin, one could be punctured by crud in the water supply, but that wouldn't necessarily cause your problem..............buttttt it could (thinking through it) if the hole were big enough to let some cooling water (but not enough) through thus reducing the pressure differential and keeping the valve on it's seat.

On the cover gasket, I have been into mine several times and still use the OEM gasket mainly because I don't have a local supplier and when I get involved in a project I want to finish it. I use blue RTV (from autoparts store) and ensure that I get a thin coating on all areas that look to have been disturbed and have had no problems with leaks.

Mark