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| Why not radiators??? I know this will... |
| Author |
Message |
    
J. Zinn
| | Posted on Monday, April 16, 2001 - 02:12 pm: | 
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Why aren't standard automotive closed cooling systems used on inboard motors? Seems to me that you could easily mount a radiator with enough ventilation and fan cooling to keep the engine temps down, and this would eliminate the nonstop heat riser corosion problems. There must be a reason for this, otherwise it would be standard practice. I have been building automotive engines for years and just can't seem to think of a valid reason why these systems aren't incorporated into boats. Please explain.. THANKS |
andrew (andrew)
| | Posted on Tuesday, April 17, 2001 - 11:49 am: |
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J. Zinn,
I will take a stab at it...
Quote:Why aren't standard automotive closed cooling systems used on inboard motors?
Many inboard marine engine installations do used closed cooling systems. Rather than using air, they use water in one of the following methods:
- An inboard heat exchanger type which circulates the closed loop engine cooling water through a heat exchanger. The heat is disipated from the heat exchanger by overboard water that is also pumped through the heat exchanger and then discharged back overboard or out through the exhaust. The heat exchanger contains tubes that allow maximum surface contact for cooling, but no actual mixing.
- An outboard heat exchanger or keel cooler, where the engine cooling loop is piped outside the hull to be cooled by the outside water before returning inside the boat and back to the engine. This could be done with pipe, but is most often done with a manufactured keel cooler that provide maximum surface area for cooling and minimum resistance.
- A combination of the first two methods by which there is an engine loop and a keel cooling loop that transfer heat in an inboard heat exchanger.
The first method is probably most common is small and medium sized boats.
Also check some of the web sites of companies that sell heat exchangers, keel coolers, and fresh water cooling kits.
The "standard" method of cooling that you are probably refering to is raw water cooling, where the overboard water is simply piped through the engine. This method does cause corrosion and salt, silt and mud buildup in the block and manifolds. It can also cause a variance in temperture in the engine, thermostats can help reduce that problem. But... if one wants to get away from raw water cooling, the solution is one of the water cooled methods, not a radiator.
Quote:Seems to me that you could easily mount a radiator with enough ventilation and fan cooling to keep the engine temps down
The prime difference in the function of a marine engine versus an automotive engine is that the marine engine is working at close to its rated load almost all the time. An automotive engine is only working at close to full load when accelerating or climbing a hill. An automotive engine has the added benefit of additional forced airflow across the radiator when travelling at speed, which would generally correspond with the high load conditions. This in itself does not mean that you cannot run a "non-moving" radiator cooled engine at high continuous load... it is done frequently in applications where stationary engines run a pump or generator. The major problem with trying to use a radiator cooling on a boat is that the limited size and available ventilation of an engine room or engine compartment make it very difficult to provide enough air for cooling and combustion. Rememeber that boats are built to keep water out, a requirement that makes it difficult to provide for a lot of air and heat exchange.
An lastly... the big reason why to use the body of water that you are floating on for cooling... because it's there... The ocean, lake, river that the boat is floating on is such a magnificent heat sink that it would be a shame not to use it. The trick is to minimize the corrosive effects of the water or at least limit them to an inexpensive component like a heat exchanger.
Thanks.
Regards,
Andrew Menkart
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Andrew (Andrew)
| | Posted on Tuesday, April 17, 2001 - 03:40 pm: |
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The cooling diagram didn't come out too well, so I will try it again here. By the way it is reprinted from INBOARD MOTOR INSTALLATIONS IN SMALL BOATS by Glen L. Witt, originally 1960, reprinted 1975 and other.
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Andrew (Andrew)
| | Posted on Wednesday, April 18, 2001 - 10:50 am: |
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J. Zinn,
Here is a German web site with a fairly complete description of fresh water cooling options...
Regards,
Andrew Menkart
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miro
| | Posted on Monday, June 25, 2001 - 10:29 pm: |
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An additrional note - the exhausts of inboards are usually cooled with the cooling su=ystem exhaust water. This is quite important especially in wooden boats which is where most of this stuff was developed historically |
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