1985 125 hp Force bypass valve question

[erosenwinkel]

I have a 1985 Force 125 hp outboard (1258x5a) that I recently had rebuilt due to overheating . I believe the impeller was shot and wasn't pumping. Also when I was pulling the engine apart to take it to the machine shop I pulled off a cover then pulled out a spring and fished out a worn/completely stuck plastic plug (bypass valve) It was solidly seized up inside the bottom of the engine and it took quite a bit of work to get it out. It has since been replaced with a new spring and plastic plug. Does anyone have an idea what the working operation of this plug/valve is? Does it need to be replaced or inspected regularly? Did its initial imobility have a contributing role in the overheat that happened? I know the impeller was not in very good shape upon its removal. After putting the engine back together, everything works great. Water pumping like a firehose, engine nice and cool. Any further explanation greatly appreciated. Thanks!

 

[Frank Acampora]

Re: 1985 125 hp Force bypass valve question

I really don't know what the engineers were thinking when they designed this bypass valve.

Normally it is in the closed position, held tight against the seat by the spring. When pressure of the jacket gets too high, perhaps with the thremostat closed, it will force open the plastic valve and bleed water directly from the inlet into the leg.

The only problem is it is prone to corrosion and failure, just as yours did. However, it is a completely unnecessary assembly and later Force engines discontinued it.

The water pump acts as a centrifugal pump at speed and excess pressure will just increase the head, lessening the amout of water delivered and thus reducing the pressure. No harm can be done to the pump by high pressure. Similarly, head gaskets and water jacket gaskets are well able to withstand any pressure the pump can develop without leaking. SO: the pressure relief serves no purpose.

With the valve stuck closed, the only result is more water delivery to the jacket and head so no, a stuck valve will not result in an overheating engine.

 

[erosenwinkel]

Re: 1985 125 hp Force bypass valve question

Thanks a bunch for the clarification. Much appreciated!
Eric

 

[drpepper]

Re: 1985 125 hp Force bypass valve question

How did you get to the impeller, and how is it driven? Did you have to pull the engine? I have 1985 19? Bayliner with a Force 1258x5a. I just obtained this boat from my father who decided he was too old to mess with it and tired of paying storage fees on a boat in NV. This boat has been in storage for 9 years, and has not been in the water for about 10 years. Spent most of the day today working on getting it fired up. Actually, after cleaning the carbs, got her to run pretty good. However, although she runs well, she is having an overheating problem. Can anyone recommend a site that has good diagrams showing how the cooling system works? And before anyone asks, yes, I attached a hose to the intake using a flushing adapter. Even remembered to turn on the water.

Thanks in advance for the help.

 

[erosenwinkel]

Re: 1985 125 hp Force bypass valve question

There is an awesome step by step sticky at the beginning of this forum that is about as "full color" as you can get. Literally . . . step by step. I took the time and put a telltale on mine. Now I know at a glance if mine is cooling, great piece of mind. Eric

 

[drpepper]

Re: 1985 125 hp Force bypass valve question

That sticky is perfect. Between the instructions and the video's, even I should be able to do this.

Thanks a bunch!