omc cooling system, still learning

[maxxman04]

came across a very helpful diagram here showing the closed loop cooling system, with center rise manifolds, which is exactly what i'm using. what i don't understand, and it's probably a simple explanation, is how raw water factors into this. it comes thru just the risers, according to the diagram, goes thru the H/E, but that's it. i'm wondering if this is to just provide cooling to the coolant in motor? again, that's probably the answer, but i need to be sure before i hook all up and hit the water with a mistake. also, i understand i need a raw water pump. i thought this was the impellers job, although i have something attached inline from the raw water intake hose (below starboard exhaust manifold) that also has my power steering hoses attached. is this the above referenced raw water pump? how does that work? i have ordered a manual, but it's taking some time to get here. any help, answers, ideas, are greatly appreciated. thank you.

 

[Don S]

Re: omc cooling system, still learning

what i don't understand, and it's probably a simple explanation, is how raw water factors into this. it comes thru just the risers, according to the diagram, goes thru the H/E, but that's it. i'm wondering if this is to just provide cooling to the coolant in motor?

The water does 2 things, cools the AF side of the Heat exchanger similar to how air does blowing over the radiator of a car.
The water also goes through the manifolds and riserss and exits the riser to cool the exhaust so it doesn't burn all the hoses.

 

[maxxman04]

Re: omc cooling system, still learning

thanks don, that makes perfect sense. but am i supposed to have a raw water pump, or do i just need to make sure hoses are hooked up correctly and call it good?

 

[Don S]

Re: omc cooling system, still learning

Yes, you have a raw water pump. What year and model engine and drive do you have?

 

[maxxman04]

Re: omc cooling system, still learning

it's an 898 series 350 v8, same series outdrive from late 70's/early 80's. i pulled entire setup from an old boat a gentleman was parting out. i've converted from the end rise to center rise exhaust, using BARR manifolds and risers. all that is installed, rather easily. now i'm installing the cooling system. i know about the engine water pump, and the impeller in outdrive. but there is that part i mentioned at beginning of thread, with my power steering lines going thru it, as well as what i assume is a water hose, coming in from outdrive.

 

[Don S]

Re: omc cooling system, still learning

Your title to this thread is omc cooling system, still learning
An 898 is a Mercruiser. OMC and Mercruiser are two different companies. Like Ford and Chevy. Only OMC went out of buisness over 10 years ago.
Sooooo, What ya got for an outdrive?

 

[maxxman04]

Re: omc cooling system, still learning

it is in fact an 898 merc setup. my deepest apologies for the confusion. i'm not sure why i listed as omc. again, my apologies to you don, and everyone else. BIG brain fart.

 

[gadget73]

Re: omc cooling system, still learning

mystery part sounds like the power steering cooler. Those are usually on the raw water side, between the transom hose connection and the heat exchanger.

 

[maxxman04]

Re: omc cooling system, still learning

i believe you are correct. i'm still a bit confused tho as to whether or not i'm supposed to have an engine mounted raw water pump. i pulled everything from a running boat, so naturally i assume i have everything. others have stated that i need a pump, others yet say the outdrive impeller does that job. am i missing something?

 

[Don S]

Re: omc cooling system, still learning

You should have a Mercruiser 1 drive, and the raw water pump is in the outdrive..... BUT, if you have an OEM closed cooling system with the manifolds being cooled with antifreeze, then you probably have an engine mounted belt driven raw water pump. You just have to look.

 

[maxxman04]

Re: omc cooling system, still learning

thank you don. i know the outdrive has a water pump (impeller) in it. the cooling system is oem, and i swear i got everything from donor boat, but never did see a pump on engine, so i guess that means i need one? thank you for your patience with me.

 

[maxxman04]

Re: omc cooling system, still learning

so after a few days of searching, asking, i've come to the conclusion that my FWC system does not need an engine driven raw water pump, as the sterndrive pump serves this purpose, but please correct me if i'm wrong. otherwise, i'll find out in a couple weeks when all is done, and i take my first trip out. thanks again to all of you and this site, it has been invaluable.

 

[gadget73]

Re: omc cooling system, still learning

If its got a seawater pump in the drive, you don't need one on the motor. I have seen odd cases where an Alpha (drive impeller type) was fitted to a boat that didn't have one originally, and for whatever reason a ski boat style transom pickup was used along with a belt driven seawater pump. I honestly don't know why that was done, but it was. Basically as long as something is pumping seawater, you're good. If it came in it's current configuration originally, then it must have worked.

 

[Don S]

Re: omc cooling system, still learning

The reason for the engine mounted pump with a full closed cooling system is because the small outdrive raw water pump does not have enough volume to cool a full system. It works fine with a block only (aka half system). But with block and exhaust manifolds, it's just not big enough in warmer water.
I had a full system on a boat with only the outdrive pump, but was fine. Of course I was in Alaska, and the warmest the water got was 50?.

 

[maxxman04]

Re: omc cooling system, still learning

you guys rock!!! thanks for all the info. i did forget to clarify tho, and again i apologize, it is a closed loop HALF system for the block and manifolds. the risers are raw water. i hope i'm stating this right, still trying to get the wording and all right, so i don't sound too dumb. thanks again.