Should the engine bay blower be always on?

[Cheechako]

Originally Posted by Tortuga's Lie

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.

A proper blower installation has an inlet, with a hose running down a bit. The fan/exit sucks hot air (rises anyway) and the inlet allows cool air entry low via the hose.

[Cheechako]

Originally Posted by dlymn

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.

Yes, a "snap disc" thermostat should work well. They are available in various temp ranges. I've used one for an exhaust temp alarm before... so I know if the cooling water has stopped! The elbow temp rises and sounds the alarm.

[Terra Nova]

A simple on-off switch does not seem o be overly difficult to learn to use properly, and at an appropriate time, for most of us.

[epiic]

Originally Posted by a64pilot

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.

Mine is mounted at the top.

It was really hot today so I am guessing it was struggling to keep up.

It's rated for 150 CFM.

[Hudson Force]

I run my blower when my diesel propulsion engine is running simply because the heat exchanger for my refrig/freezer is in my engine room. I use a cheap $25 plastic blade blower that last me about 6 years between replacements.

I choose what is efficient and significant for my situation. I expect everyone to do this.

[markpierce]

My diesel engine draws air into the engine compartment. Rarely use the exhaust fan unless entering the compartment with the engine hot.

[boatpoker]

Originally Posted by leftbrainstuff

No mention of a blower in the ABYC fuel system docs.

See ABYC H-2, Minimum blower capacity, page 8

[Dockhead]

Mine has a thermostat, but it runs all the time, unless I manually shut it off.

It's a big one with a big duct out the transom, and it makes a very large difference in engine room temperature.

A hot engine room is definitely not a good thing, neither for the efficiency of the diesel engine, nor for the health of the gear you have mounted in there, including the alternators.

[Tortuga's Lie]

Originally Posted by Dockhead

A hot engine room is definitely not a good thing, neither for the efficiency of the diesel engine, nor for the health of the gear you have mounted in there, including the alternators.

Good point about the alternator.......they definitely like it cooler

[GordMay]

Originally Posted by SteveInMD

... Maybe someone else can chime in on the exact max temp recommendation.

The maximum temperature of the engine room should never exceed 140 degrees F, within 3/4" of any electrical equipment (ie: Alternator); and should never exceed 115 deg. F anywhere in the engine compartment.

[rwidman]

Now that that's been settled ......................................

On a gasoline powered boat, the blower doesn't blow, it sucks. "Sucker" doesn't sound right so it's called a "blower". It is designed to suck possible gasoline vapors from the bottom of the engine compartment. There will be a tube from the lowest part of the engine compartment to the blower and another tube from the blower to vents in the hull. You can put your hand or a tissue next to the vent and see or feel the air moving away from the boat.

The blower should be run for five minutes before starting the engine(s) and after fueling and before starting the engine(s).

If you have some sort of blower with a diesel engine, you'll have to figure it out unless your boat came with instructions. The first hint is whether it pressurized the engine compartment or creates a vacuum (as with a gasoline engine). Running the engine in a partial vacuum doesn't seem like a good idea. I would think if anything, a fan would be used to force additional cool air into a diesel's engine compartment.

My diesel boat has no blower.

[Crew of Turning]

I have thought of installing a couple of computer fans in the engine compartment of our boat. The idea was to push the warm out into the cabin in the spring and fall to lift the temperature. Have not done but has anybody tried and got results?

[Hudson Force]

Originally Posted by rwidman

Now that that's been settled ......................................

On a gasoline powered boat, the blower doesn't blow, it sucks. "Sucker" doesn't sound right so it's called a "blower". It is designed to suck possible gasoline vapors from the bottom of the engine compartment. There will be a tube from the lowest part of the engine compartment to the blower and another tube from the blower to vents in the hull. You can put your hand or a tissue next to the vent and see or feel the air moving away from the boat.

The blower should be run for five minutes before starting the engine(s) and after fueling and before starting the engine(s).

If you have some sort of blower with a diesel engine, you'll have to figure it out unless your boat came with instructions. The first hint is whether it pressurized the engine compartment or creates a vacuum (as with a gasoline engine). Running the engine in a partial vacuum doesn't seem like a good idea. I would think if anything, a fan would be used to force additional cool air into a diesel's engine compartment.

My diesel boat has no blower.

rwidman's observations here are clear and valid; however, many might not consider the term blowing to be directional. I would think a "blower" could move air in or out of an engine room. The blower that moves hot air out of my diesel engine room does not create a partial vacuum. I have places where air can enter by means of an open opposing vent as well as unsealed doors and lockers leading from my forward cabin, aft cabin and center cockpit.

I would elect to have the air from my engine room expelled with cooler, fresh air entering. Blowing air into my engine room would increase the heat, odors and potential carbon-monoxide entering my cabins.

This concern would be true for my thoughts about "Crew of Turnings" plan to blow air from his engine room into the cabins. I don't believe that this is a safe plan regarding potential CO poisoning.

[rwidman]

Originally Posted by Crew of Turning

I have thought of installing a couple of computer fans in the engine compartment of our boat. The idea was to push the warm out into the cabin in the spring and fall to lift the temperature. Have not done but has anybody tried and got results?

That would not be a good idea. Your engine compartment would normally have some fumes or smells, and in the case of a gasoline engine, possibly gasoline vapors.

It's not terribly difficult to tap into the engine's cooling system and run the coolant through a heater in the cabin, similar to how a car heater works. I believe you can buy these ready to install.

[a64pilot]

You want to have the engine room at a slight low pressure, that way any smells or fumes or hot air will be drawn out and some air will be drawn in from the inside of the boat, even if your engine room is vented.
If it were at a slightly higher pressure, then hot air and any fumes and or smells would be forced out of the engine compt and blown into the inside of the boat, even if the room is vented.
I do not want any hot air inside of my boat, cause I am forever seeking warm weather, and I can do without any smells either.

The very slight negative pressure will have no effect on engine performance, and or it will be canceled out by having cooler air, we operate at seal level of course and I would bet that a blower and or engine intake air results in a no more than 100 or 200' pressure differential, which is negligible, you don't lose measurable power going up in altitude 100' in your car.
But my argument is the manufacturer spent money putting it there, if it wasn't needed, then why did they waste the money?