So i run a jet so i know how that is cooled. I know how a outboard is cooled. But how is a traditional I/O or V drive cooled?
Do they ahve a traditional water pump or whats up?
Raw water cooling (Uses water directly from jet, pickup through block)
Closed water cooling (Uses a closed loop system with heat exchanger) Heat exchanger is cooled by raw water.
I got this for you on a boat survey site
There are two basic types of cooling systems.
One is what is called a closed system. This is a system where fresh water or antifreeze type coolant circulates inside the engine. This system is similar to a car engine where the antifreeze in the radiator is circulated through the engine.
The second type of cooling system is called a raw water cooling system. In a raw water cooling system seawater is circulated through the engine instead of fresh water or antifreeze and that sea water cools the engine directly. When the boat is used in a fresh water lake this system is excellent but when a boat is used in salt water the salt water circulating inside the engine tends to shorten the life span of the engine.
Closed Cooling System with heat exchanger
Why are cooling systems important in boat engines? Salt water circulating inside an engine will shorten the life span of the engine. In addition overheating problems associated with boat engines are very common and often result in engine failure.
Since the fiberglass hulls on most boats will outlast the engines, the condition of the engines and their expected life span becomes a primary concern. Replacement of a gasoline engine will commonly cost $5000 to $10,000 depending on the type of engine and the labor involved. Diesel engines will cost about three times or more that this to replace.
Raw water Cooled system
The cooling system has a direct correlation to engine life expectancy . The type of cooling systems becomes a factor in older boats. Estimated engine life for a fresh water cooled inboard engine is 1500 hours and for a salt water cooled engine is less than 1000 hours.
With a fresh water cooled engine, the engine is cooled within a closed system by antifreeze coolant. The coolant exchanges the engines heat to sea water within a heat exchanger. Salt water or raw water is pumped into a heat exchanger which cools the coolant which then circulates throughout the engine. This works very similar to a radiator in a car where the coolant is cooled by the car fan or by air as the car is driven. In a heat exchanger the salt water or raw water is what cools the engine coolant.
In an engine that is directly cooled by salt water, corrosion and rust build up inside the engine. This restricts the water way sometimes causing the engine to operate at higher temperatures, and may corrode the internal cooling system of the engine causing engine failure. A fresh water cooled engine does have its own problems to contend with, like maintenance of the cooling system, so there are plus and minuses to each type of installation.
Just a few words on outboard engine here. All outboard engines are raw or salt water cooled. They are subject to the type of corrosion caused by salt water. However since they sit vertically salt water drains from them naturally. While this does provide some protection to the cooling system of the engine, the engine will still deteriorates internally due to exposure to salt water.
Last edited by Jet Mad; 05-22-2011 at 01:40 PM.
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I/O's have either a raw water pump in the drive or have a pump attached to the front of the engine somewhere (not the normal car style water pump although they can have that also.) It will either pump water thru the engine in an open cooling system, like your jet only a little more to it than that, or pump the lake/sea water thru a heat exchanger on one with a close cooling system. V-drives have a raw water pump, usually run off of the cam, at least on most of the setups I've seen, then to the engine like your jet is plumbed.
Last edited by gregb; 05-22-2011 at 01:29 PM.
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My boat has a water pick up through the hull just in front of the transom. There is also a belt driven marine water pump for when there is not much ram effect from the pick up.
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To be more specific on this, I/Os have a rubber impeller that needs to be replaced from time to time and a pickup on the lower unit... (Volvo drives have the easiest set up I have seen on an I/O for changing the impeller)
Ouboards have a rubber impeller that needs to be replaced from time to time and the pickup on the bottom of the leg, sometimes relocated with a low water pickup...
V-drives (a man's boat) has a rubber impeller run off of the cam/timing gear and a pickup at the back of the hull OR on the plate... External plumbing from the pump to the typical car pump inlets...
My nephews mastercraft has a typical car water pump on his 350 chebby and a external rubber impeller pump to feed the car mota pump... Also has a heat exchanger on the cold water inlet that cools the velvet drive...
Last edited by 2manymustangs; 05-23-2011 at 03:40 PM.
Just attached a catheter from all the beer drinkers on the boat directly to the heat exchanger.
Late model Bravo or Volvo I/Os have a recirculating pump on the front of the block that is identical to the auto type except they are marinized. There is also a belt driven raw water pump, which supplies lake water to the engine.
When the engine is cold, the thermostat is closed and cooling water is circulated through the engine by the block mounted pump. As the engine warms, the thermostat opens and the heated water is dumped overboard. This water is replaced by the raw water pump. The thermostat maintains the proper engine temperature.
Engine cooling systems with a heat exchanger are similar to a car...the system is sealed, has a coolant overflow tank, and the coolant is circulated by the block mounted pump. The system also has a raw water pump. The coolant is routed through a heat exchanger...the device has inlets and outlets for coolant and raw water. The heat in the coolant is transferred to the raw water and dumped overboard.
Last edited by rrrr; 05-24-2011 at 11:59 AM.