Closed Cooling System (Half)

[Lawrencemd]

I would like to get your opinion on the setup of a half closed cooling system for my 250 6cyl boat engine. What I was thinking of implementing is keel pipes cooling the engine and trans oil cooler (closed system) and cooling the marine manifold by pumping in raw water from a thru hull fitting into the marine manifold then out and into the wet exhaust. A seen in the below pic. What size pump do u think I would need for the raw water side (in gph)?

[mwatts]

I always respect guys who attempt to do DIY practical keel cooling... ;)

A few thoughts:

You might have a better chance of a good answer in the "DIY Marinizing" section
Where's the thermostat? It will be hard getting the engine at a good operating temperature without a thermostat. As it looks now, it will probably run too cold. Never leave the thermostat out when designing your own cooling system.
The thermostat should connect to a valve which will redirect coolant from a continuous flowing loop to the engine, so it starts to get cooled too. You don't want the coolant standing still in the keel pipes, as it could get very cold, putting strain on the engine if it suddenly starts flowing to the engine.
You could use a heat exchanger, cooled by the fresh water, as an alternative to the keel pipes.


Just my $ 0.02. There are bigger experts on this forum with possibly better ideas, but the design you currently have is sub-optimal I think.

[thudpucker]

Watts says good things.
My experience with a 327 Chevvy engine in Cook inlet AK with just the Heat exchanger was great. You dont need a Keel Cooler.
One more thing you might want to add is a Water Pressure guage to the Engine coolant. It will tell you about trouble before the engine temp guage will.

You just cannot run any engine without a T-stat. With the Heat exchanger and normal 50/50 Anti-freeze mix you'll have an engine that might outlast you!

Make sure your sea water pump is accessible for cleaning and have a good strainer on the inlet.

[steele m.a.]

I'm building a similar system right now . It's for a 240 ci. mercury straight six .
Original , the engine pumps raw water up , through itself and it's exhaust system , and then overboard . I live on the West Coast , on Vancouver Island
and this type of cooling leads to internal corrosion . What I'm doing is modifying the original to have a closed system . In order to do this , some
things have to change . The best way to cool glycol based fresh water
is to pump it through a heat exchanger that is bathed in cold seawater .
Instead of putting an external keel cooler out where it can be damaged ,
what we're doing is mounting aftermarket automotive transmission coolers
inside the hull , with open ports bringing raw water in around them .
The raw water surrounding these radiators enters and exits these dedicated
radiator housings as a function of forward boat speed .
The modifications required to the original stock hull involve fiberglassing in
radiator containment boxes inside the bottom surface of the hull , underneath the floorboards , and creating raw water passages at either end of these cooler boxes to allow raw water to enter and exit as much as possible .
In Canada's cool waters , this is effective .
This doesn't solve your exhaust pipe cooling problems though . The effectiveness of a marine raw water exhaust cooling system is that it
is sacrificial , basically you are simply pouring cold water all over a hot exhaust pipe , and throwing out the result .
This is very effective , if hard on the exhaust system , but there is almost
no way around it .
For the same engine cooling glycol to be used to cool the exhaust header
sounds like it would work , but doesn't .
The exhaust header is much hotter than the engine , and boils off your
system's precious ethylene glycol .
markalfredsteele@yahoo.ca