fresh water cool engines

[salmonee]

If the engine is fresh water cooled, does that mean you can start the motor w/out having the boat in the water? I assume this is the case, because it has a radiator for cooling the motor. Right?

 

[slasmith1]

Re: fresh water cool engines

You still need to hook it up to the muffs becaus it still uses raw water through the heat exchanger to keep it cool. you just don't have any raw water going through the block.

 

[erikgreen]

Re: fresh water cool engines

To be accurate, you can start it up without muffs very briefly and not damage the engine, but you will damage the outdrive if you have one. It requires water flow to not melt certain internal parts and to cool the exhaust.

The engine has a small amount of coolant water in it, along with the cylindrical (usually) heat exchanger. But that small amount of water heats up pretty quickly, so more than a 10-30 second run will damage the engine too.

Now if you have a system like a keel cooler, then you probably have enough thermal mass to run for a couple of minutes without damaging the engine, and since keel cooled boats are typically inboard, you won't damage the drive/prop/shaft. But you might still melt part of the exhaust if you have a "wet" exhaust.

So practically speaking, you need muffs, a tank, or to have the hull sitting in water to start the engine.

I don't think I've seen a boat yet with a radiator, although there are some with heater cores. Boats generally aren't air cooled, they exchange heat with the water.

Erik

 

[QC]

Re: fresh water cool engines

Salmonee,

The radiator confusion may have come from an analogy I made comparing a fresh water cooled engine's "heat exchanger" with a radiator. The heat exchanger is where the "closed" or "fresh water" part of the cooling system (surrounding the engine) is cooled by the lake or sea water (often called raw water).

With a typical radiator the engine coolant is cooled by ambient air which is never seen on a small boat. The air is drawn across the radiator either by a fan or vehicle motion or both. In the case of a marine engine with fresh water cooling, the closed system's heat is cooled by ambient water that is drawn up from the lake or ocean by the "raw water pump" and pumped into a fairly large cylinder that is about 4 - 6 inches in diameter and 12 -18 inches wide and it's called a "heat exchanger", from there the raw water usually cools the manifolds and exhaust and then exits back to the lake. Inside the heat exchanger there is a series of tubes that contains the engine coolant which is pumped by the engine's traditional water pump. This pump is usually called the circulating pump as it simply circulates coolant throughout the engine and through some sort of heat exchanger. On your car that heat exchanger is called a radiator (see above) and on a boat it is called a heat exchanger oddly enough . . . Both could technically be referred to as radiators as they both radiate heat, or heat exchangers as they both exchange heat. One from engine to air, and the other from engine to "raw water". Hence the confusion.

The raw water pump is the one with the rubber impeller. It can be located in the drive in the case of a Mercruiser Alpha and most OMC drives, or the raw water pump can be mounted on the front of the engine in the case of a Volvo or Mercruiser Bravo, or a traditional inboard. In all of these cases, the rubber impeller would be damaged very quickly by running it out of the water without some sort of water supply directly to the raw water pump such as "muffs". Muffs are a set of rubber thingees that fit over an outdrive's water intake grates and allow a garden hose to supply water similar to what would happen if those grates were under water . . .

 

[salmonee]

Re: fresh water cool engines

Salmonee,

The radiator confusion may have come from an analogy I made comparing a fresh water cooled engine's "heat exchanger" with a radiator. The heat exchanger is where the "closed" or "fresh water" part of the cooling system (surrounding the engine) is cooled by the lake or sea water (often called raw water).

With a typical radiator the engine coolant is cooled by ambient air which is never seen on a small boat. The air is drawn across the radiator either by a fan or vehicle motion or both. In the case of a marine engine with fresh water cooling, the closed system's heat is cooled by ambient water that is drawn up from the lake or ocean by the "raw water pump" and pumped into a fairly large cylinder that is about 4 - 6 inches in diameter and 12 -18 inches wide and it's called a "heat exchanger", from there the raw water usually cools the manifolds and exhaust and then exits back to the lake. Inside the heat exchanger there is a series of tubes that contains the engine coolant which is pumped by the engine's traditional water pump. This pump is usually called the circulating pump as it simply circulates coolant throughout the engine and through some sort of heat exchanger. On your car that heat exchanger is called a radiator (see above) and on a boat it is called a heat exchanger oddly enough . . . Both could technically be referred to as radiators as they both radiate heat, or heat exchangers as they both exchange heat. One from engine to air, and the other from engine to "raw water". Hence the confusion.

The raw water pump is the one with the rubber impeller. It can be located in the drive in the case of a Mercruiser Alpha and most OMC drives, or the raw water pump can be mounted on the front of the engine in the case of a Volvo or Mercruiser Bravo, or a traditional inboard. In all of these cases, the rubber impeller would be damaged very quickly by running it out of the water without some sort of water supply directly to the raw water pump such as "muffs". Muffs are a set of rubber thingees that fit over an outdrive's water intake grates and allow a garden hose to supply water similar to what would happen if those grates were under water . . .

Thanks for the clarification. Very well put.