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Old 03-17-2013, 07:11 PM   #1
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Question 1996 270SCR Engine Compartment Ventilation

Hello forum.
I searched and searched for a thread on this but have not been able to find anything on it. And I don't believe I would be the only person asking this question.

I have 1996 270SCR with a single 7.4L Mercruiser. The engine compartment is only ventilated by a single electric blower to exhaust fumes from the engine compartment. There is no forced air vents to bring in fresh air. Every other model of boat has these. The boat has 4 ports under neath the stern seating bench, one of which has the powered blower the other 3 are simply ported to different areas of the compartment. But by no means can any air be forced in through these openings. They are underneath the stern bench with the openings to the sky covered by the bench bottom about 2" above.. Attached are two pictures, one of the stern whcih shows hows the current ventilation is under the stern bench seat, and another one I found of someone selling his boat who appears to have added the vent on the side of the hull port side with some sort of silver grill.

Has anyone compensated for this by adding in Venturi or other vents to the side of the boat? Has it made a difference? What did you use to do it?

Thanks.

[ATTACH][/ATTACH][ATTACH][/ATTACH]
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Old 03-18-2013, 06:30 PM   #2
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Are intake should be passive, air exhaust should be active. Fuel vapor is heavier than air, so it sinks to the lowest point in the bilge. The 3 intakes ensure they are routed to different parts of the engine compartment for even air ditribution. The blower should be attached to the lowests vent hose that goes to teh bottom of the bilge. This sucks air directly from the location where the fule vapor woudl be and blows it overboard. This creates a vaccuum that sucks in fresh air to replace the vapor. The three hoses ensure the fresh air is distributed evenly throughout hte compartment.

What you're proposing is to actively force air into the bilge to displace the fuel vapor. This will disturb the fuel vapor and spread it evenly through the engine compartment. The outbound vent will still be sucking from the bottom, however now most of the fule vapor is being actively displaced around the entire engine compartment space instead of alowing it to collect at the bottom. It will need to slowly allow the fuel vaport to settle in order to be sucked out.

IMHO, active inboard venting is not a great idea. Allow the boat to function as it was designed.
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Old 03-19-2013, 01:43 PM   #3
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Thanks for the reply shrew. I didn't really consider the disturbance of the bilge air while running the blower to exhaust bilge fumes, being that the blower is attached to the hose and you are correct does go to the lowest part of the bilge. I was thinking more along the lines of "passive air" circulation while underway allowing the engine to breathe.

I spoke with a Maxum engineer some time ago about this and it took some convincing on my part and for the engineer to actually look through past drawings to believe me when I told him they designed the boat without any forced air into the engine compartment. He was unable to give me a satisfying answer to the question.

Models until 1992 had them, and then again starting in 1997. Hoping to hear if anyone has had the same concern or tried this.

1992 Vent.jpg1997 side vents.jpg
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Old 03-19-2013, 01:45 PM   #4
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Default 1997 270SCR Engine Compartment Ventilation

Hello forum.
I searched and searched for a thread on this but have not been able to find anything on it. And I don't believe I would be the only person asking this question.

I have 1996 270SCR with a single 7.4L Mercruiser. The engine compartment is only ventilated by a single electric blower to exhaust fumes from the engine compartment. There is no forced air vents to bring in fresh air. Every other model of boat has these. The boat has 4 ports under neath the stern seating bench, one of which has the powered blower the other 3 are simply ported to different areas of the compartment. But by no means can any air be forced in through these openings. They are underneath the stern bench with the openings to the sky covered by the bench bottom about 2" above.. Attached are two pictures, one of the stern whcih shows hows the current ventilation is under the stern bench seat, and another one I found of someone selling his boat who appears to have added the vent on the side of the hull port side with some sort of silver grill.

Has anyone compensated for this by adding in Venturi or other vents to the side of the boat? Has it made a difference? What did you use to do it?

Thanks.

Current Vents.jpgEngine Compartment Vent.jpg
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Old 03-19-2013, 04:39 PM   #5
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Duplicate Thread has been merged with active thread.
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Old 03-21-2013, 05:48 AM   #6
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Thanks shrew I couldn't figure out how to relocate it.
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