Engine compartment venting question

[L8-Again]

New to boat ownership here. I have read lots of great information on this site over the past year but only recently registered. Wanted to get informed before being tempted to post!

1979 Cordova, Mercruiser (Chev 350) SE106 (Alpha I)

I did some wiring work recently to make things look organized under the hood. The battery grounds were connected to the exhaust manifold bolts and I didn't like it, among other wiring rat nests. I relocated the exhaust vent tube to below the oil pan. Previously it was being squished by the hood because it went down the side by the starter. Now is comes in behind and the hood doesn't put any pressure on it.

I got to thinking about running the blower. Most of the time I forget to turn it off after starting and run around on the water. When I shut down I hear it running and wonder if anyone else has the same memory problem I do! I tend to run it all of the time for fear of "blowing up!"

What do you think? Is running the blower constantly a problem or not?

Also I only have 1 hose going under the hood. I read another post that there should be 2 so I will be adding one to the port side and terminate it at the top of the hood. My vent grills have two spots on each to connect a 3" hose to. I am guessing that I could run 4 hoses in but that it is only really necessary to have 2. What do you think?

Thanks in advance.

 

[Black as]

Re: Engine compartment venting question

Everyone will have an opinion on this one but I run mine 3 minutes before start up because I have a large air space under the floor and secondly it only has to blow up once

And while on the water I have it running all the time just to be safe than sorry

 

[carcraze]

Re: Engine compartment venting question

Yep there will be a few opinions.
On mine I run my blower for 3 mins prior to starting. I do not leave it running but have forgot it on before, running it should not be a problem. When under way the compartment should be venting regardless of the blower running though.

I have twins and have 4 hoses per side of boat with 2 blowers 1 per side. 2 exit per side with the blower hose being down in the bilge.

My incoming vent hoses are plumbed carb height out in front of the motors again 2 per side.

 

[johnny be good]

Re: Engine compartment venting question

I have a 350 in my boat and allways lift the hood just to take a peak before starting, you never know what can be lurking under there . But I do agree with running blowers 3min. before if your not going to lift the hood and I run my blowers any time I am just puttin along

 

[wire2]

Re: Engine compartment venting question

There's often a warning on the dash to run the blower for 3-4 minutes before starting and keep it on at slower speeds.

I also pop the engine covers before the 1st start-up of the day to check for water in the bilge, and sniff for gas.

The vents on most boats are on the side, one facing forward, (to scoop fresh air in), the other facing to the rear to draw it out.

The typical design is 2 hoses on the inlet vent, 1 to the bilge, 1 to the upper engine level. Also 2 hoses on the exit vent, 1 with the blower to the bilge, 1 to upper engine.

At speed, there's enough air stream velocity to effect good circulation through the engine bay to keep it ventilated without the blower on. But it won't hurt anything to leave it on.

 

[H20Rat]

Re: Engine compartment venting question

At speed, there's enough air stream velocity to effect good circulation through the engine bay to keep it ventilated without the blower on. But it won't hurt anything to leave it on.

The amount of air from the scoops while moving is actually pretty small for most boats. The bigger reason it is safe at speed is because your engine itself is pumping far more air through the compartment, much more than the blower or scoops could anyway.

 

[seabob4]

Re: Engine compartment venting question

There is no problem with running the blower while underway. One thing you do want to do is to not let blower hose rest in the bilge, it will deteriorate quickly. NMMA/ABYC states the ends, or terminus, simply needs to be in the lower 1/3 or the bilge/engine compartment area...

 

[180shabah]

Re: Engine compartment venting question

Many installations have mutiple hoses. You NEED one.

It should start low in the bilge (lower than the starter) but still be high enough so as not to be under bilge water - it will not pump it out and thus makes your blower useless. It should then run to the suction side of the blower, from the blower the hose continues to the exhaust vent (it should be rear facing)..

The other hoses are ther to make people feel good - getting fresh air to the engines etc, but they do very little. As long as your intake vent/s are in the engine compartment, you're good to go.

Blower MUST be run prior to start up (even if you open the hatch) and during slow speeds. It will not hurt anything at all to let it run all day. Mine is 4yo and runs startup to shutdown, besides they are cheap and easy to replace if it does die.

 

[Aviator5]

Re: Engine compartment venting question

I wonder why manufacturers dont do this:
hook the blower circuit to the ignition key, so when you turn the ignition on it turns on the blower, put a timer to disable starter and ignition for 3-4 minutes, so you can't start the motor rigt away, and leave the blower running as long as motor runs, and shut it down automatically when you shut down the motor.

 

[rbh]

Re: Engine compartment venting question

Two air scoops/vents on each side, one is for the blower and faces to the rear, the other scoops air in at travel, loovers face forward.

 

[seabob4]

Re: Engine compartment venting question

I wonder why manufacturers dont do this:
hook the blower circuit to the ignition key, so when you turn the ignition on it turns on the blower, put a timer to disable starter and ignition for 3-4 minutes, so you can't start the motor rigt away, and leave the blower running as long as motor runs, and shut it down automatically when you shut down the motor.

Because that would cost a lot more than a little decal telling you to run your blower for 4 minutes...

 

[Aviator5]

Re: Engine compartment venting question

I don't think it will cost much more, $100 bucks or so. There is nothing to it.
Chinese parts will cost as much as that decal.

 

[H20Rat]

Re: Engine compartment venting question

I wonder why manufacturers dont do this:
hook the blower circuit to the ignition key, so when you turn the ignition on it turns on the blower, put a timer to disable starter and ignition for 3-4 minutes, so you can't start the motor rigt away, and leave the blower running as long as motor runs, and shut it down automatically when you shut down the motor.

believe it or not, safety...

i'm floating and about to get run over by a passing boat, or I notice that I've drifted into an unsafe area while I had my feet up reading a book.

A loud beeper or warning light yes, but not disabling the ignition.

 

[180shabah]

Re: Engine compartment venting question

believe it or not, safety...

YUP, timer circuit wouldn't know the difference between the first start of the week, or I just picked up a downed skier and need to get out of the way cause the approaching boat isn't paying attention.

 

[JoLin]

Re: Engine compartment venting question

believe it or not, safety...

i'm floating and about to get run over by a passing boat, or I notice that I've drifted into an unsafe area while I had my feet up reading a book.

A loud beeper or warning light yes, but not disabling the ignition.

Bingo. Have the manufacturer decide when I can and can't start the motor? Bite your tongue!

As for leaving the blower on, I've forgotten and done it. No harm, no foul. When running at low speed, it's actually recommended that you switch it on as you don't get much air flow through the bilge.

 

[Stachi]

Re: Engine compartment venting question

I would wire mine to the run position... safest bet if you think about it...

 

[L8-Again]

Re: Engine compartment venting question

Thanks for all the great information!

You guys are fantastic!

 

[Jeepster04]

Re: Engine compartment venting question

I wonder why manufacturers dont do this:
hook the blower circuit to the ignition key, so when you turn the ignition on it turns on the blower, put a timer to disable starter and ignition for 3-4 minutes, so you can't start the motor rigt away, and leave the blower running as long as motor runs, and shut it down automatically when you shut down the motor.

Ive often wondered that. I would go a step further and have a micro switch on the carb that shut the blower off once the engine was given a certain amount of gas. That way it would be fully automatic. Kick on when you turned the key on(Although our boat has an annoying BEEEP when you turn the key on till you start the engine), stay on for 3-4 minutes, then stay on while the engine is at idle until the switch is tripped.

Wouldnt want to disable the ignition what so ever though. Would only want it to kick on when I turned the key, then allow me to start it whenever I wanted.

Other than that, I leave the blower on in our boat all the time on accident. Nothing wrong with it.

 

[roozter2550]

Re: Engine compartment venting question

I would wire mine to the run position... safest bet if you think about it...

you could wire 1 blower to run off of the toggle switch and also from the key on position using a relay.

pos wire from toggle switch to blower and also separate pos wire from ignition switch to relay which when energized turns on the blower regardless of toggle switch.

this way you could turn on the blower before starting as usual but if forgotten, it would at least come on when you turned the ignition on and off when you shut down the engine.

 

[Fordiesel69]

Re: Engine compartment venting question

I want to buy a compartment sniffer. It will sound an alarm if there is gas fumes, and will also tell you if the blower has run long enough.

Anyone know where I could buy an affordable one?