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Old 19-01-2017, 09:30   #1
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Should the engine bay blower be always on?

Ever since I purchased the boat, the blower has never turned off when the engine is running. Is this normal?

The reason I am asking is because its starting to sound different and I am guessing it has more hours on it than it should.

My previous boat had the blower on a relay to shut off after a set period of time.
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Old 19-01-2017, 09:36   #2
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Re: Should the engine bay blower be always on?

Even for a gas/petrol engine the blower only needs to run for 5min or so before starting then not at all.

Maybe there isn't a big enough air inlet to the engine compartment and the blower makes up for this.
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Old 19-01-2017, 09:40   #3
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Re: Should the engine bay blower be always on?

Unless you have a gasoline engine, heat problems or fumes, the blower doesn't need to be run at all. Some people run their blower for engine room cooling in warm climates or to solve a fume problem.
I have 4 diesels in my engine room and rarely run the blower. And then only to clear some unwanted smell, like curing paint.
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Old 19-01-2017, 09:47   #4
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Re: Should the engine bay blower be always on?

Some boats like mine use the blower to exhaust excess heat, if you blower inlet is at the top of the engine compt, that is what it is for, the ones to eliminate fumes of course draw from the lowest point in the bilge.
Blowers are real cheap, I run mine as the manufacturer intended, lower engine room temps have to be a good thing
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Old 19-01-2017, 09:53   #5
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Re: Should the engine bay blower be always on?

High engine room temps cause the air to be thin (less oxygen per cubic foot) and degrade engine performance. I don't recall the exact recommended max temp but I think it's 140 F. Run the blower all the time if needed to keep it cool in there. Maybe someone else can chime in on the exact max temp recommendation.
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Old 19-01-2017, 09:58   #6
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Re: Should the engine bay blower be always on?

Run it whenever the engine is running and for awhile after engine is shut off.
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Old 19-01-2017, 10:02   #7
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Re: Should the engine bay blower be always on?

I like to run it to extract the heat, unless it's cold out. A separate switch is nice.
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Old 19-01-2017, 10:12   #8
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Re: Should the engine bay blower be always on?

I've never run my blower. 18 years in San Francisco. Diesel engine. Runs great. Blowers were a holdover from gasoline engines. Useful to remove heat and smells. If you have smells you have other issues. Heat removal is good. I never had that issue.
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Old 19-01-2017, 10:20   #9
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Re: Should the engine bay blower be always on?

my diesel engined boats have never had one. my gasoline powered boats i left it on while running , prestarting and other times when fumes could well be an issue.
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Old 19-01-2017, 10:43   #10
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Re: Should the engine bay blower be always on?

At this point in this discussion, someone usually jumps in with equations showing how many CFM the engine moves, vs. the amount a blower moves.

At any rate, I'm convinced that my puny little blower doesn't make much difference one way or the other if the engines are running. If not, it's kinda loud and annoying. I might consider using it to cool the engine room faster after shutdown, but I'm not convinced it's a match for all the thermal mass in there anyway.

Also, a blower large enough to make a difference might compete with the engines for air, if the ventilation wasn't adequate.
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Old 19-01-2017, 10:56   #11
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Re: Should the engine bay blower be always on?

Quote:
Originally Posted by epiic View Post
Ever since I purchased the boat, the blower has never turned off when the engine is running. Is this normal?

The reason I am asking is because its starting to sound different and I am guessing it has more hours on it than it should.

My previous boat had the blower on a relay to shut off after a set period of time.
In the same manner as is the case on our boat, on the 409 the blower, mounted in the transom is connected to a vent tube that runs to the upper portion of the engine bay while two "static" (i.e. unpowered) vent tubes run from the transom to the lower area. The blower is designed to extract hot air from the engine bay and ensure the engine, while in operation, is receiving relatively cooler ambient air. That ensures the engine runs cooler itself and combustion is more efficient. FWIW there are rarely "unnecessary" parts on a boat. Most are included by the designer/builder to fulfill a specific, intended, purpose.
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Old 19-01-2017, 10:58   #12
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Re: Should the engine bay blower be always on?

This is an interesting topic of discussion and perhaps a thermal/mechanical engineer may chime in but I am pretty sure that there is a direct relationship between the volume of the engine compartment and the effectiveness of the blower to remove heat, as well as the capacity of said blower. Also, air has to be able to enter the engine compartment too.
I personally will only use the blower when running the engine for more than an hour or so to remove unwanted heat. My engine compartment is not all that large and excess heat is probably not desirable. If I had a huge compartment like you find on large powerboats, or large center cockpit cruisers, than probably doesn't make that much difference. Of course, I am thinking diesels here.
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Old 19-01-2017, 11:43   #13
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Re: Should the engine bay blower be always on?

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Originally Posted by Adelie View Post
Even for a gas/petrol engine the blower only needs to run for 5min or so before starting then not at all.

Maybe there isn't a big enough air inlet to the engine compartment and the blower makes up for this.
A blower wont counteract a flow restriction issue. It's not a positive displacement pump.

There is usually enough leakage for this not to limit engine power. Any pressure tight engine room will have an inlet.
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Old 19-01-2017, 11:55   #14
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Re: Should the engine bay blower be always on?

Most engine rooms are not classified as explosion proof. The use of a blower is more about feeling safe.

However the ABYC calls for a ventilation blower where heating systems are fitted. No mention of a blower in the ABYC fuel system docs.

Our blower is most useful for clearing the engine room when our espar heater is not combisting correctly. I usually complete my preventative maintenance on the fuel misting mesh before this happens.

We also use our blower for a minute prior to staring our engine, generator or espar heater. If there was a combustible atmosphere present the electric arcing on the blower brushes would ignite them. Propane is the only flammable gas that would cause this.
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Old 19-01-2017, 12:41   #15
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Re: Should the engine bay blower be always on?

I have a small blower that I hoped would remove heat from the engine compartment. I have a switch in that area and so forget to use it. I bought a button thermostat, the type used on hot water services and plan to attach it to the motor somewhere so that the fan turns on when the engine gets hot and off when it cools a little. One day I migt put it on.
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