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Old 12-10-2012, 20:41   #1
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Engine compartment air fan is noisy.

I have an inline fan blowing air out of the engine compartment. It make's a lot of noise ( and that's being polite !). It's operated by an on/off switch. Could I use a rotary potentiometer type switch to cut down it's speed and hence the noise ? Where can such a switch be purchased ?
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Old 12-10-2012, 21:10   #2
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Re: Engine department air fan is noisy.

If it is a diesel engine, you do not require a blower. Turn it off.
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Old 12-10-2012, 21:26   #3
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Re: Engine department air fan is noisy.

A blower is typically used for a few minutes prior to starting the engine. It removes volatile gases which may accumulate from petrol/gasoline engines or, if they are not isolated from the engine room, from battery banks.

If you are worried about volatile gas/or suffocants otherwise, install a gas detector which will record gasoline vapour, carbon monoxide, LPG, refrigerant gases etc.
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Old 12-10-2012, 22:08   #4
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Re: Engine department air fan is noisy.

Is this the kind of inline fan you're talking about?

If it is, it should be pretty quiet. You can replace it with a new one for less than thirty bucks.

Order it here: Rule 4" Inline Blower 12V - MFG#240
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Old 13-10-2012, 11:32   #5
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Re: Engine department air fan is noisy.

Let me give you the full story. I had a survey on my sailboat yesterday, and the surveyor said my diesel engine was being starved of air. He suggested running the fan to blow air into the engine compartment. So... could I get an answer to my question please - if you know one. THX.
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Old 13-10-2012, 11:39   #6
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Re: Engine department air fan is noisy.

I can understand the increased air supply for the diesel, but there can be other reasons too. I use the 3" Rule #140 just to keep the heat down as my air heat exchanged refrig/freezer shares the engine room space. These little plastic blowers often only last about five years with a lot of use, but they only cost $25 to $30. Sometimes they get real noisy before they fail.
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Old 13-10-2012, 11:43   #7
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Re: Engine department air fan is noisy.

Yes you can use a rheostat. NAPA autoparts sells them... old school heater rheostat with bracket. My boat has one of those in line blowers and it's pretty darn noisy.... although i dont hear it with the engine on... maybe it's going bad too...

The fan sucks air out usually. If your engine cant get enough air, you need more inlet open area. Is the engine just sucking air from the bilge?or are there any openings to allow air into the engine compartment?
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Old 13-10-2012, 11:45   #8
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Re: Engine department air fan is noisy.

my guess is that fan is blowing air OUT of the engine not in
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Old 13-10-2012, 11:45   #9
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Re: Engine department air fan is noisy.

Your ventilation does not need to be powered. Add some vents that have no fans. You will need to cut a suitable area that allows air into your engine space and then put louvers, a grating or something similar to keep from going through the ventilation hole that you cut. It does not need to be something very large either.

I am surprised your boat manufacturer did not provide adequate passive ventilation.

What it sounds like is that you may not be getting is adequate cooling to your engine space, given your engine is starving of air. An engine space whose air temperature is far above ambient air temperature is not a good thing for a number of reasons. Passive ventilation is always better than powered ventilation if it is practical.

Explosive gasses other that gasoline fumes can be found in and possibly explode in an enclosed space such as your engine space. So you want to keep some sort of forced draft ventilation in your engine space, but you won't have to run it all the time if you create adequate passive ventilation.
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Old 13-10-2012, 12:25   #10
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Re: Engine compartment air fan is noisy.

You might want to use passive intakes and outlets if you engine is being starved of air.



I have never been on a boat that required an active (electric or otherwise) intake.
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Old 13-10-2012, 12:47   #11
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Re: Engine compartment air fan is noisy.

We have a blower that blows into the engine compartment and works very well too. We have on occasion needed to motor across the English Channel which can take 14 hours. Running the engine for that length of time heats up the engine compartment to the point that even the cushions on top are warm. Therefore we run the blower which is directed at the batteries first before the air moves on to the engine.

Those running large alternators or hot alternators with external regulators might also benefit from additional cooling.

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Old 13-10-2012, 14:25   #12
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Re: Engine compartment air fan is noisy.

Google DC Motor speed control.

Edit: Read this.
http://www.passagemaker.com/magazine...ponent&print=1
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