Engine Ventilation Fan always on - SailNet Community
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post #1 of 25 Old 06-27-2019 Thread Starter
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Engine Ventilation Fan always on

My friend bought this boat.
2003 Beneteau 361

It is a diesel I believe Yanmar.

It is very loud in the cockpit due to the ventilation fan.

This is the first boat I've been on that wired the fan to be always on.

Is it recommended, necessary?

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post #2 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

Not necessary.
Normally when the engine starts or, alternativly, when the key is turned on.
Because the engine is expected to be on those fans are not quiet, nor are they economical.

They are on 24/7? whilst the engine isnt on? while the boat is alone on the dock/mooring?

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post #3 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

Weird... Should be on when key switch is turned... if not re wire or add a on off switch. But it should be on and probably withdrawing air from the engine compartment.
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post #4 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

Quote:
Originally Posted by davidpm View Post
My friend bought this boat.
2003 Beneteau 361

It is a diesel I believe Yanmar.

It is very loud in the cockpit due to the ventilation fan.

This is the first boat I've been on that wired the fan to be always on.

Is it recommended, necessary?
Our batteries are in the engine room. The temp gets up to 100-110 on a hot day. So we wired a 6" computer fan to blow cooler air in. Its completely silent and uses next to nothing in elec.
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post #5 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

Glad for this question because I am also confused.

I've got a fan in my diesel engine compartment on my sailboat that I never turn on. Maybe I'm wrong. I believe it is set to exhaust air not supply it. I'll admit I don't understand the whole idea.

When we re-powered a diesel powerboat, one of the big concerns was getting enough air in. My understanding is that diesels consume a lot of air. Intuitively, don't you need to fill those cylinders up with air, compress it with oil, cause an explosion, and then exhaust the whole mess through the usual wet exhaust? Doesn't this amount to the diesel being a multi-horsepower vacuum cleaner sucking all the air out of your engine compartment? We actually increased the size of the air intake for the power boat engine compartment to be sure it wasn't starved for air based on recommendations from the diesel manufacturer.

So what's the idea with an exhaust fan on a diesel? I get it for gas, fumes igniting and blowing you up, seems like a fine idea to avoid that .
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Last edited by capecodda; 06-27-2019 at 08:12 AM. Reason: fix
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post #6 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

Diesel engines especially old ones... don't smell good. Further they are in confined spaces which get hotter an hotter. Exhausting air will mean that cool clean air will find it's way in and replace the hot sticky air. Smells and some heat are exhausted. If you blow IN to the engine box...some of the smelly hot air will likely find its way into the cabin. YUCK. Wifey complained of diesel smells so I reverse the fan and the smell is way way less... tolerable. Engines need combustion air so it makes sense to do "air changes" in the engine room.
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post #7 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

My current boat has a fan, for exhaust only. I also have a vent which directs the air pulled by ol' Perky over the alternator, and then it get used by the engine. The fan I have set up on a manual switch to exhaust the engine bay once the engine is shut down to exhaust the fumes and dissipated heat from the engine. That helps quite a bit, to reduce the fumes and heat down below.
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Last edited by SV Siren; 06-27-2019 at 08:47 AM.
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post #8 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

OK, then it seems to me the fan would be best used right after the engine is shut down.

No need to run it while the engine is running. A fraction of HP of exhaust cannot compete with many HP of engine vacuum, but after you shut down, the engine is still hot and maybe smelly, exhaust could cool it down for an hour or something like that?

So is that the proper use?
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post #9 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

My boat had a nice older squirrel fan. It would draw some amps too.
I removed it and went fanless.
Its port is the run for the solar wiring.
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post #10 of 25 Old 06-27-2019
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Re: Engine Ventilation Fan always on

The exhaust fan in a Diesel engine compartment serves two purposes. First, they provide for continuous fresh air flow, so any exhaust leak is more likely to be evacuated than enter the salon. This evacuates general odors better too. Neither are absolute. They also provide a better supply of cooler air than the 100+ degree compartment air it would otherwise be inhaling. Cooler air is more efficient combustion and cooler engine compartment temps are better for longevity. Some motors, like ours, actually have intercoolers specifically designed to cool the intake air.

The exhaust fan should always be running, when the engine is running. Not really following the OP. I canít believe it runs 24/7, so fix that, if itís the case. If the engine is running, itís hard to imagine the fan is whatís causing all the noise.
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