Insulate engine cover.....bad idea???

[thunderroad]

My 69 Formula w/160 Mercruiser has a fiberglass engine cover. The other day I was running the engine on the muffs in the driveway and got to wondering if insulating the inside of the engine cover would make it sound quieter. Now...it's not terribly loud as it is, but hey...if it makes it easier to hear the stereo, why not? So I unzip a sleeping bag and drape it over the cover. It's considerably quieter. So... I was wondering...what if I glued some kind of foam insulation to the inside? There's plenty of room. The cover is fairly large and the inline 6 is pretty skinny. My question is, could this possibly inhibit the cooling process for the engine? I realize that newer boats have a cover that is usually padded and covered on the outside, but I don't want to mess with the outside of mine. It's in perfect shape and is a pretty cool design. I'm thinking some sort of foam, about 1" thick, glued to the inside with spray adhesive. Is this a good or bad idea?
What sayeth the masses?

 

[Boomyal]

Re: Insulate engine cover.....bad idea???

My '75 Gulfstream has a hand laid fiberglass dog house. It has no insulation and has a 302 ci Ford inside it and it is reasonably quiet. My '76 Beachcraft, with 302 Ford, has a chopper gun laid fiberglass doghouse, with an inch of foam blown on the inside, then a light coating of chopper gun glass shot over the top to give it some protection. That BeachCraft is intolerably noisey. Same engine, slightly different doghouse material, one with insulation and one without and the one without is quieter. Go figure. The only other difference, and I really can't see how that would affect noise, is that the quiet one has an OMC Stringer outdrive and the loud one has a Merc I oudrive.

All that being said, if you have adequate engine compartment ventilation, insulate away. Can't hurt and may improve things.

 

[reelfishin]

Re: Insulate engine cover.....bad idea???

You may want to try Dynamat or something similar, they use it in custom cars and trucks. It's a thin, sound deadening mat that is self adhesive and very thin. They use it to quite interiors and absorb sound.
http://www.dynamat.com/

 

[thunderroad]

Re: Insulate engine cover.....bad idea???

The dynamat stuff looks like the ticket. I might look around locally and see if I can find something similar. The thing isn't uncomfortably loud as it is, but the older I get, the more I appreciate quiet.
It's kind of a weird feeling to be looking for things to do to my boat. Usually they just slap me in the face. I'm gonna enjoy it while it lasts....I know someday the worm is gonna turn.

thanks

 

[lmannyr]

Re: Insulate engine cover.....bad idea???

Try finding fire resistant material. You don't want to put sound deadning material that will speed up the human deadning effect. But really, look into this aspect of the material for additional safety. You'll get less noise and better fire protection (or more time to gather your flotation device to go overboard).

Good luck, I'll probably look into this when I get my engine rebuilt.

 

[Chris1956]

Re: Insulate engine cover.....bad idea???

My SeaRay had OEM foam on the inside of the motor box. Appeared to be standard eggcrate type foam rubber.

On the other hand, they have the mylar bubble wrap type insulation. That stuff should glue up very well, stay in place and doesn't add any weight.

 

[Zero Balance]

Re: Insulate engine cover.....bad idea???

I insulated my cover with 2" standard foil back foam board. Not really flame resistant but in the event of a fire I dont think the foam board will exasterbate the situation. I covered the seams with aluminum foil tape. In all I think it cost about 40 bucks and worked out quite well. I too can now appreciate my music better.