osco to mercruiser

[777memaw]

I have a 1978 mercruiser 350 260 HP. I had osco manifolds with center riser. The dealer told me I could use the mercruiser center riser that is for 1983 to 2002. Well I got the manifolds and they only have 4 bolts my engine has 6 bolts. He says they will work but can't tell me how to plumb them since my set up has 3 hoses. Does anyone know if these will work on my engine and have a diagram as how to plumb them? My osco took water in at the bottom of manifold out the top back to engine and out the riser .

 

[Bondo]

Re: osco to mercruiser

Well I got the manifolds and they only have 4 bolts my engine has 6 bolts. He says they will work

Ayuh,.... Manifolds are rigid enough, you'll never miss those 2 bolts...

Donno what you've got for available ports on those manifold/ risers,...
You might possibly need a different T-stat housing....

 

[777memaw]

Re: osco to mercruiser

Thanks Bondo. Does anyone know how to plumb this with 3 hoses?

 

[legoman67]

Re: osco to mercruiser

Thanks Bondo. Does anyone know how to plumb this with 3 hoses?

so you have closed cooled manfolds im assuming?

if so you need one port on each side of the manifolds, this hooked into the closed cooling loop that also goes through your block. then you need the correct plate that goes between the manifold and riser to block the seperate circuits from mixing in water passages in the connection(for when both are raw cooled), then the third hose which is raw water needs to go to the port on the riser, which allows it to exit with the exhaust...

 

[777memaw]

Re: osco to mercruiser

The water comes in the out drive no antifreze. It comes out off thermostat housing to bottom of manifold out the top of the manifold back to thermostat housing then from thermostat to riser. The gasket between riser and manifold is closed no water goes directly from manifold to riser.

 

[777memaw]

Re: osco to mercruiser

My thermostat housing has 6 hoses coming out of it. They are all above the thermostat I think thermostat sits in intake manifold right? So if I want to go to one hose going to manifold I should be able to use the top two hoses since all 6 are above the thermostat and block off the other four hoses right or am I full of it??????

 

[777memaw]

Re: osco to mercruiser

anyone know?

 

[Bondo]

Re: osco to mercruiser

You might possibly need a different T-stat housing....

Ayuh,... Post a picture, or see my quote...

 

[777memaw]

Re: osco to mercruiser

I can't post pictures not that smart!!! OK I was wrong the thermostat is in the top of the housing. I can not find a housing that brings water in the starboard side and out to the water recirculating pump on the same side. All I need to know is if I can plug 4 of these 6 outlets and run the other two to the bottom of the manifolds and what gasket to use for the riser, I have gaskets with 2 holes and others with 4 holes.

 

[legoman67]

Re: osco to mercruiser

put it back the way it came appart, the only thing different if any will be the locations of the ports on the manifolds and risers.

 

[777memaw]

Re: osco to mercruiser

I plumbed it the same way it was with 3 hoses to each side. I can't imagine why I couldn't have done it ewith one or two hoses. Branded new mercruiser manifolds runs great but with the temp gauge at 160 risers are to hot to leave your hand on for very long. Do you think this is normal????

 

[legoman67]

Re: osco to mercruiser

is there water flowing through the risers?

 

[777memaw]

Re: osco to mercruiser

Yes there is water to the risers. Water goes from thermostat housing to bottom of manifold out the top of the manifold back to the engine thru the thermostat then to the riser. It has a block off gasket between the manifold and riser.

 

[777memaw]

Re: osco to mercruiser

anyone