engine compartment ventilation

[hrifraf]

I am a relatively new A25 owner, and I have a question about ventilation in the engine compartment. My boat has the original Volvo MD3B engine.

In the documentation that came with my boat there is a Volvo service bulletin about engine compartment temperatures. The Bulletin states that the maximum temp should be 140 degrees. My boat has an engine compartment thermometer, which regularly reads over 160 degrees after a couple of hours of running.

The Bulletin states; "A condition for good engine function is that the temperature in the engine room is kept as low as possible in order to avoid smoke, output losses and problems with the electrical equipment". I haven't noticed any of these problems, but am concerned about them anyway.

I was wondering if anyone has tried to enhance their engine compartment ventilation by adding a fan to one of the vent ducts, or by some other means.

Cheers;
Harald
hrifraf at gmail dot com

[DougSea]

Hi Harald, and welcome to AOG!

I have a very different boat but since I have the setup you're asking about I thought I'd share.

Our 35 has large air inlets in the hull sides for "normal" engine air and ventilation. It also has a pair of clamshell vents with 3" hose and in-line blowers. These are set up with one as an exhaust and one as an inlet. It was this way when we bought it and I've just assumed that the inlet hose in particular would help stir up the air in the engine room and promote even cooling. Also, as hot air rises, you'd want the exhaust blower to draw from as far up in the compartment as practical.

I don't find the need to use the blowers often, but if I'm going to be staying aboard after a long run when everything is warm I use the blowers to bring the engine room temp down, and by extension, the floor of the saloon. I also use them on very hot days, again to boost the cooling of the engine room beyond the normal airflow.

I mentioned my thru hull side vents at the beginning of this post since I'm not familiar with your boats engine room air supply. If you ONLY have the clamshells and you place blowers in the lines you would be restricting airflow UNLESS the blowers were on. Just something to be aware of.

[N4QC]

This is a repost...

For some basic background information on air ventilation see:

http://www.yanmarhelp.com/i_vent.htm


Note that one should have an equal air exhaust opening for the air intake opening…

More technical calculations show that a diesel setup requires more surface area of air intake than a gas setup. A turbo diesel requires even more.

Additional air is required to help cool the engine room as other machinery, such as the transmission, generator, etc., need to have the heat they disperse removed.

Local conditions may also play a factor in the amount of air needed in the engine room. These conditions would include water and air temperatures.

Forced air intake and air exhaust can allow for a reduction in the size of openings.

Heed the warning about any ductwork delivering air directly to the air intake of the engine – DON’T…

Calculations can also be done on a CFM basis as well as a square inch basis…

The diesel mantra is: clean fuel, and adequate clean air…

In my case, while under way, my hull vents, port and starboard, are set up to act as exhaust vents. I have a third vent on the side of helm station above the gunwale. This too acts as an exhaust vent, (it was intended as an air intake vent for the diesel). A new source of air intake was built into my steps going from the aft deck to the helm station. This step vent serves as a plenum for an 8”, 1500 CFM (rated) blower which directs air into the engine compartment. I also added a CO detector in the cabin as the engine room is now slightly pressurized.

Hope this helps,

[hrifraf]

Thank you gentlemen for your informative comments.
I feel that the two 3-inch cowl vents in the A25 engine compartment are plenty for combustion, but I don't think they do much for engine compartment cooling.
I will take a look at my engine compartment and see how hard it would be to add some more ventilation, perhaps with a fan, without restricting the existing airflow.

[NickScheuer]

I just towed our Albin-25 NORD STJERNE home to Rockford from Larson's in Waukegan where they were checking out consistant overheating at 2000rpm as indicated by the engine temp gauge. While there, I had them change the oil and winterize. The Supervisor said the engine wouldn't drain coolant from the plug in the side untill they dislodged "a lot of sand", likely from a too shoal bottom. They performed additional flushing, but said I should repeat this myself when in the water next neason. The Superivsor also said our engine compartment is "very tight" and recomended additional vetillation, mentioning that some folks add fans. I like the idea expressed above inregard to "in" and "out" fans.