Should the engine bay blower be always on?

[a64pilot]

Originally Posted by Elie

I agree completly on this idea. In fact too much heat in the small engine space, may create problems like overheating of alternator(its murder!). But, powerfull fans are noisy. I'm lookin for some sort of thermostatic switch that would start the fan only when temperature reach a certain point. But wher to find this type of thermostatic fan?...

Buy an adjustable thermostat separate and wire it into the fan, then when set temperature is reached, fan comes on.
There are many of course, quick look on Amazon found this one for $10, seems it will handle a 20 amp load at 14VDC, but I just did a quick glance
https://www.amazon.com/12V-Programma...ble+thermostat
I can't hear my blower over the Diesel engine, even at idle. You guys must have some really noisy blowers?

[a64pilot]

Originally Posted by jakkum

A 4 ltr engine, 4 stroke, moves 4 ltr of air, every 2 revs. So running at 2000 rpm it moves 4000 ltr of air every minute.
What does a blower move?

So your intake is at the top of your compartment?
Mine isn't either, but the hot air is. I figure it will cost me about $5 a year to maintain the engine room blower like the factory built it.

There are I guess two ways to look at this

1. Factory was stupid and wasted time and money installing a blower unnecessarily
2. Factory knew what they were doing

[Caliber40]

I run mine while operating and for 20 minutes after shut down. I have a variable timer so I can regulate the after run time.

Blowers are cheap on eBay....I keep 2 or 3 as spares....expect to change them every 1000 hours of blower run time.

If they reduce heat a little why would you not want one?

[jamhass]

Some use a blower to specifically cool the alternator

[wrwakefield]

We use an engine room exhaust blower mainly to push heat into the cockpit enclosure when boating in cooler weather.

Of course, it can be diverted outside the enclosure when needed for venting heat, fumes, etc.

One consideration perhaps worth noting for those of us with automatic [or manual] fire extinguisher systems in the engine room: The fire extinguisher should be wired to kill the engine(s) when activated [with a manual override switch...] and any exhaust blowers should be wired to this same circuit.

The goal being not to suck out all the extinguishing gas before it has had time to have effect...

Cheers! Bill

[boatpoker]

Originally Posted by wrwakefield

We use an engine room exhaust blower mainly to push heat into the cockpit enclosure when boating in cooler weather.

Of course, it can be diverted outside the enclosure when needed for venting heat, fumes, etc.

One consideration perhaps worth noting for those of us with automatic [or manual] fire extinguisher systems in the engine room: The fire extinguisher should be wired to kill the engine(s) when activated [with a manual override switch...] and any exhaust blowers should be wired to this same circuit.

The goal being not to suck out all the extinguishing gas before it has had time to have effect...

Cheers! Bill

Narrow inlet, in the dark, beam seas, shitty weather. Think I want to make the decision when to shut down an engine not some automatic system.

Directing leaking exhaust gasses into a cockpit enclosure seems less than wise to me.

[a64pilot]

Originally Posted by jamhass

Some use a blower to specifically cool the alternator

I had thought to do that too, and I asked the alternator builder about it and his answer was, yes it will help, but to blow the air at the rear of the alternator as that is where most of the heat is. I didn't know that.
My alternator makes good power, but the temperature protection kicks in in less than 10 min or so which limits power quite a bit, if I can cool it, maybe I can get it to make more power

[wrwakefield]

Originally Posted by boatpoker

Narrow inlet, in the dark, beam seas, shitty weather. Think I want to make the decision when to shut down an engine not some automatic system.

Directing leaking exhaust gasses into a cockpit enclosure seems less than wise to me.

Very valid points, Boatpoker...

No one should design, implement, or use such systems casually...

The override switch on auto-engine shutdown is a critical component in the fire suppression system. You can just shut off the auto-shutdown function entirely, or over-ride it to re-start the engine(s) once a fire is extinguished. Your choice.

Regarding possibility of CO and exhaust gasses being vented from the engine room: as with inside the boat, there is a combination CO/smoke alarm in the enclosure [and the engine room; 7 total on the boat...] And of course, if the air smells bad [e.g., fumes], we divert the airflow to outside of the enclosure... Otherwise, it has proved to be a good source of heat when motoring from the outside cockpit in winter...

Full disclosure: We often wimp-out and use the inside [pilothouse] steering station in cold wx when motoring...

Thanks for making sure everyone understands the possible repercussions of these choices.

Cheers! Bill

[a64pilot]

Originally Posted by wrwakefield

One consideration perhaps worth noting for those of us with automatic [or manual] fire extinguisher systems in the engine room: The fire extinguisher should be wired to kill the engine(s) when activated [with a manual override switch...] and any exhaust blowers should be wired to this same circuit.

The goal being not to suck out all the extinguishing gas before it has had time to have effect...

Cheers! Bill

I believe some boats at least are wired this way from the factory. I helped a couple on a Big Sportfisherman this Summer, a 65' Viking. Their engines wouldn't start, turns out they had an overheated battery, the fire suppression system had detected that, closed the huge air louvers, removed power from the blowers and disabled fuel to the engines and armed, but luckily not fired the fire bottles.
My little sailboats automatic fire extinguisher discharges on an overheat, I think it has a strip of metal that melts like a buildings fire sprinkler system

[wrwakefield]

Originally Posted by jamhass

Some use a blower to specifically cool the alternator

We ducted the engine room fresh air inlet to end just above the alternator. [It is passive- no blower...]

The engine [and exhaust blower when on] pulls in quite a bit of air over the alternator. I haven't done enough measurements to be meaningful, and the alternator still diverts to lower output about 15 mins into a new cycle [when starting from an ambient temp engine room...]

I do monitor the engine room temp, and it consistently stabilizes at 115°F. That drops almost 5° if the exhaust blower is on.

The alt temp needs to be documented more closely with and without benefit of the fresh air duct in close proximity to see if this was a worthwhile addition... But it can't hurt...

Cheers! Bill

[wrwakefield]

Originally Posted by a64pilot

My little sailboats automatic fire extinguisher discharges on an overheat, I think it has a strip of metal that melts like a buildings fire sprinkler system

A64,

Our Kidde FyreWatch suppression system is also triggered as you describe. It also has an electrical contact on the activation system that fires a relay which is wired to power the shutdown solenoid on the engine on the relay NO contacts, and kill the exhaust blower on the NC contacts.

Simple but effective. [Yet they are proud ($$) of this capability...]

May none of us ever discover how well it all works... [Everything tests OK... except popping the bottle; can't afford that on a routine basis... We do have it weighed annually, or whenever close to a service facility, however...]

Cheers! Bill

[a64pilot]

If a bottle fires with the engine running, its almost instantly sucked through the engine and gone, does shut down the engine though. Like someone else said an engine is a pretty effective air pump
I have three of those bottles, one in the engine room, one in the Laz with the generator and one in the electrical compt behind the breaker panel. That one I think has a good chance as its a confined space with no airflow through it.

[roverhi]

Have had two boats without Mechanized engine room ventilation. Have had to power for more than a day with both, one in oppressive heat in the doldrums, without any problems. Engine rooms had significant openings to the lazarette so cracked the hatch to increase ventilation. If I had a gasoline engine would run the blower constantly.

[Safari38LH]

Originally Posted by Terra Nova

Run it whenever the engine is running and for awhile after engine is shut off.

I run a blower if running the engine for more than a hour. After shutdown someone told me to turn off the blower before the engine room cooled off so you don't suck moisture in with no heat to dry it out. Makes a lot of sense.

[Terra Nova]

Originally Posted by Safari38LH

...someone told me to...

OK, whatever.