I installed a compartment suction fan after installing an external alternator regulator. The alternator was running much hotter as it was working much harder with the external reg. and needed cooler air inside the engine housing.
Last edited:
I never run the blower fan, it serves no purpose and its noisy.
I am intrigued by @Ralph Johnstone duct work. We have a high output alternator in a tiny engine compartment. Increasing air flow over the alternator is good for the alternator. Not sure I would add a suction fan as it would compete for air with the diesel. I'd just let the diesel draw the air in over the alternator.
I am intrigued by @Ralph Johnstone duct work. We have a high output alternator in a tiny engine compartment. Increasing air flow over the alternator is good for the alternator. Not sure I would add a suction fan as it would compete for air with the diesel. I'd just let the diesel draw the air in over the alternator.
Given the amount of air and therefore ventilation from an operating diesel which inherently draws lots of air for combustion, it would have to be a huge fan to contribute any value toward cooling.
It's been recommended to me to have two fresh air ducts placed to help cool the alternators. That is coupled with an exhaust fan to remove hot air from the engine compartment. I'd have to go look at the specs, but it's not a huge exhaust blower.
dj
p. s. I run twin alternators...
dj
p. s. I run twin alternators...
I have a high output alternator with external regulation. I installed a suction fan to pull hot air from the alternator and exhaust it outside. It is only a 3" or 4" fan and the exhausted air is very warm. The end of my hose is right next to the alternator.
Originally I had no exhaust fan and the engine compartment heated to over 175 F. This was way too hot as I found out when my engine compartment halon extinguisher was triggered. Now with the exhaust fan my compartment runs about 135 F.
Originally I had no exhaust fan and the engine compartment heated to over 175 F. This was way too hot as I found out when my engine compartment halon extinguisher was triggered. Now with the exhaust fan my compartment runs about 135 F.
It really depends on where the air flow is. In my engine compartment the vent hoses lie aft of the engine and low, very close to the air intake for the diesel and very far away from the alternator. The cooling the fan would add would be trivial.
Always wondered who was spying on me when I was at working late at night installing my Cooling Exhaust Fan™. Too similar to be coincidental. Either that or great minds really do think alike. My original temperature was about 150℉ and dropped near to 100℉. My Balmar ARS-5 then able to put out more amperage as it was set up to start reducing output at alternator temp. of 180℉.
The entire underside of the engine is open to the bilge area and draws air over the cold hull surface. The surface area is quite big and does a nice job of supplying cool air to the engine. With all that cross- sectional area for air flow, I doubt there is any drop in air pressure within the engine enclosure, which BTW, also doubles as a Nike shoe box:
Always wondered how much air a Yanmar 2GM20F draws at cruising RPM:
Not a lot of combustion air intake for a diesel engine compared to a 3" Detmar axial fan. The flow from the exhaust fan is something less than open flow (158 CFM) as the manufacturer does no include a fan curve.
Engine compartment blowers for diesels are applicable while under way not at start up like gasoline engines. Diesel is producing vapors capable of ignition when heated to 120f. If there is a leak and it’s onto the block then the diesel is producing ignitable vapor. This is where a blower would come into play. Keeping the concentration of the vapor below its combustible concentration. Interestingly diesel needs only 1/2 the ratio of vapor to atmosphere as gasoline and requires almost 1/2 the ignition source temperature of gasoline. It’s claim to fame is that it’s needs a lot of energy to produce vapor (120f) but once there, it’s very dangerous.
My Beneteau was wired so that the blower runs when the engine runs. Both the intake duct (no blower) and the exhaust duct (powered) exit through the transom.
I confess that I don't use mine, because it doesn't work, the switch (which I think is the blower switch) has no wires on it, and I don't even know where the blower is located or where the ducts are. 
Maybe I should look into this.
Maybe I should look into this.
Last edited:
I use my engine room (it is actually a walk in engine room) exhaust fan to circulate air when working in there, more than anything. If I were serious about an engine room or compartment fan, it would blow in, not out. Diesels require a lot more air that you might imagine.
@MikeHoncho Thanks for the reminding us that diesel is not as safe as we might to believe. It piqued my interest so I read up on the explosive properties of diesel. The Lower Explosive Limit (LEL) of diesel is 1% and the upper level is 6% according to OSHA. Below 1% by volume diesel will not ignite and above 6% it will not ignite.
Curious about what 1% would look like in my engine compartment, I calculated the rough volume at 41,472 in3.(about 2'x4'x3' = 24 ft3). A fluid gallon has 231 cubic inches. If my math is correct (and sometimes it is off) it would take about 1.79 gallons vaporized to reach a 1% level. (414.72/231= 1.79). That is quite bit of diesel.
Meanwhile, with the diesel running at cruising speed (using @Ralph Johnstone's calculation) the engine is consuming 31.42 ft3 of air per minute. In my engine compartment the air is being changed every 45 seconds (24ft3/31.42ft3 = .76).
If my logic is correct the engine would have to vaporize more than 1.76 gallons per minute to reach a 1% level. That's a lot fuel to vaporize. In order to attain that rate the injector pump would have to fail and spray diesel on the exhaust manifold or a very hot alternator. And then it would need an ignition source.
I think a fire or explosion from diesel inside our small engine compartments with small diesels is a low probability event, however that does not negate the possibility. Promptly dealing with and fuel leaks and a clean bilge and engine compartment might well be the best preventative measure. Incidentally, propane gas leak sensors are also sensitive to diesel vapors and will sound an alarm.
The more likely scenario for diesel explosion might be while fueling a near empty tank on a hot day. Vapors in the tank could reach explosive levels and a spark from static electricity generated while fueling could trigger an explosion. Boats with twin diesels of a larger hp might be more problematic as one diesel could spray fuel onto the other causing the ignition.
Another issue worth considering is how a small fire onboard could ignite the diesel and cause the fire to rapidly expand.
Note, the calculations here are rough back of the napkin calculations and not meant to be definitive. The goal is to put the issue Mike raised in context, yes it is a concern, no it is not as much of a concern as gasoline, propane, and other flammables onboard. Almost all of the organic solvents we use, Acetone, mineral spirits, alcohol, etc. are combustible and explosive at some level. Some are safer than others.