New Under-Hood Insulation - PeachParts Mercedes-Benz Forum

Gregory · #1 04-08-2014, 10:54 AM

1984 300SD engine compartment hood insulation

The old black foam insulation stuck to the underside of the hood turned to dust with a finger poke, and some of it was missing. A friend mentioned that without the insulation, the heat from the engine would cause the paint to quickly fail on that spot of the hood.

I went to Lowes and got a roll of aluminiumized Mylar bubble sandwich insulation. I needed a 3-foot wide roll to do it in one piece, so naturally I had to buy the 4' x 25' roll for $43. I rationalized it by saying, that's enough to do it 4 times to get it right, and it costs about the same as the replacement insulation from the auto parts store.

The hood came off the car pretty easy with a helper. I unplugged the wires to the squirter heaters, and the feed tube for the squirters. The clips and pins came out of the hood hinges easy. Be careful not to drop the back edge of the hood onto the windshield as you remove it. There is a trick when reinstalling the hood pins. Two of them have a bump under the head of the pin that fits into a detent in the pin socket. Turn the pin so those line up or you won't fully seat the pin or get the retaining clip on it.

I put the hood shinny side down on a folding table with blankets for padding.

I used a plastic scraper to remove most of the old foam. It came off easy and smelled strongly of diesel saturation. The big pieces when straight into a nearby trashcan. The 5 gallon shopvac came in handy to suck up the smaller bits and dust and avoid a mess.

I used a 3-inch razor scraper to clean most of the old glue and remaining pad off the metal.

I rolled out the bubble insulation and cut it large. I slowly and carefully trimmed it to the shape of the front of the hood so that it would tuck under the lip. As I worked my way around, trimming it bit by bit I kept tucking it under the lip. This kept it from sliding around so it was easy to make accurate cuts.

When I got on the down-sun side of the hood, it was way too bright with the sun in my eyes, reflecting off the insulation, so I rotated the hood to be working on the up-sun side again.

After the piece was fully trimmed and tucked into the lip, I carefully untucked the front half of the insulation and folded it up 90 degrees. I sprayed 3M contact cement in the middle area of the hood and up on the insulation, avoiding getting it too close to the edges. I waited about 10 seconds for the cement to start getting tacky and carefully lowered the insulation onto the hood trying to avoid wrinkles, and tucked the edges back under the lip. I took a break for about 10 minutes to let the glue set.

Then I untucked the back half of the insulation and repeated the glue process.

I'm fairly pleased with how this project turned out. There are some small wrinkles, but nothing serious. What I like best about this type of insulation is that when a fuel line pops off, it won't get saturated with diesel, like the foam does.

SD Blue · #2 04-08-2014, 12:32 PM

I would like to know how well this holds up. My concern, due to the heat locally, was the underlying hexcell construction was made of plastic. However, it the mylar sufficiently reflects the heat, this may not be an issue.

I agree, the foam pad has to be replaced about every 2-3 years around here and much less if it ever absorbs diesel fuel.

Marshall Welch · #3 04-09-2014, 12:56 AM

Also interested in how that will hold up. My story- I installed a sheet of aluminum-mylar coated thick foam I bought from a marine supply company. It has a mineral-loaded barrier layer sandwiched in between two layers of foam.

It works well, but it's heavy. After a few months, it started to come loose, so I removed it, and re-applied adhesive. The second time, I used 3M Super Trim adhesive to hold it on, and that works better than the 3M Super 77 Adhesive did. I've had it on for about 5-6 years now- it's holding up well.

Clemson88 · #4 09-26-2024, 12:18 PM

Quote:

Originally Posted by Marshall Welch

Also interested in how that will hold up. My story- I installed a sheet of aluminum-mylar coated thick foam I bought from a marine supply company. It has a mineral-loaded barrier layer sandwiched in between two layers of foam.

It works well, but it's heavy. After a few months, it started to come loose, so I removed it, and re-applied adhesive. The second time, I used 3M Super Trim adhesive to hold it on, and that works better than the 3M Super 77 Adhesive did. I've had it on for about 5-6 years now- it's holding up well.

Is that Super trim adhesive the Super Trim 90?

JHZR2 · #5 09-26-2024, 08:05 PM

Quote:

Originally Posted by Clemson88

Is that Super trim adhesive the Super Trim 90?

I always use the 90. It’s “high temp” and available from the Home Depot. Lasts as long as the foam in those panels.

Marshall Welch · #6 10-08-2024, 12:08 AM

Quote:

Originally Posted by Clemson88

Is that Super trim adhesive the Super Trim 90?

"3M Super Trim Adhesive", "#08090". The can is probably 10 years or more older. I also fabricated about 6-8 retaining screws using nylon screws and nylon capped nuts; speed nuts, and 4-6 inch long strips of galvanized steel (sheet metal), which were slid into the holes in the steel reinforcements running along the inside of the hood. I punched corresponding holes in the sound deadener material.

The adhesive is starting to come apart along the outer edges, and in the center, but not yet to a degree to warrant removal of the material and re-applying adhesive. If I recall correctly, I used about 1-1/2 or more spray cans of the adhesive. After I installed the insulation, I compressed it by first laying a sheet of corrugated cardboard over the engine, then putting lots of wads of crumpled paper all over on top of that, and then closing the hood for several hours or longer; overnight probably wouldn't be a bad idea. I might have done it for overnight, but haven't looked back at any service records I might have recorded. I would do the same thing in the future if I needed to do it again.

I recommend getting two cans of the stuff- I would apply copious amounts -- follow the instructions. It's not cheap, but neither is your time to re-do the job. I hope this helps.

Edit: I also used fender washers on each of the retaining screws, to help distribute the weight of the insulation sheet. I believe that the fender washers are stainless steel- they were significantly thinner and lighter weight than any galvanized steel washers I had access to at the time. Either would probably work, though.

Edit2: Regarding the 3M Super Trim Adhesive- the can I still have says: "Net wt 19 oz (539g)".

JHZR2 · #7 10-14-2024, 08:50 AM

Quote:

Originally Posted by Marshall Welch

"3M Super Trim Adhesive", "#08090". The can is probably 10 years or more older. I also fabricated about 6-8 retaining screws using nylon screws and nylon capped nuts; speed nuts, and 4-6 inch long strips of galvanized steel (sheet metal), which were slid into the holes in the steel reinforcements running along the inside of the hood. I punched corresponding holes in the sound deadener material.

The adhesive is starting to come apart along the outer edges, and in the center, but not yet to a degree to warrant removal of the material and re-applying adhesive. If I recall correctly, I used about 1-1/2 or more spray cans of the adhesive. After I installed the insulation, I compressed it by first laying a sheet of corrugated cardboard over the engine, then putting lots of wads of crumpled paper all over on top of that, and then closing the hood for several hours or longer; overnight probably wouldn't be a bad idea. I might have done it for overnight, but haven't looked back at any service records I might have recorded. I would do the same thing in the future if I needed to do it again.

I recommend getting two cans of the stuff- I would apply copious amounts -- follow the instructions. It's not cheap, but neither is your time to re-do the job. I hope this helps.

Edit: I also used fender washers on each of the retaining screws, to help distribute the weight of the insulation sheet. I believe that the fender washers are stainless steel- they were significantly thinner and lighter weight than any galvanized steel washers I had access to at the time. Either would probably work, though.

Edit2: Regarding the 3M Super Trim Adhesive- the can I still have says: "Net wt 19 oz (539g)".

That many cans seems excessive. Ive always used about half to 3/4 can and it has stuck for years. Eventually the foam covers start to decompose.

On occasion I’ve had a small area come loose, but an injection there has fixed it. Again, never needing multiple cans. I have to wonder if you actually use too much???

Skid Row Joe · #8 03-03-2020, 11:51 PM

Quote:

Originally Posted by SD Blue

I would like to know how well this holds up. My concern, due to the heat locally, was the underlying hexcell construction was made of plastic. However, it the mylar sufficiently reflects the heat, this may not be an issue.

I agree, the foam pad has to be replaced about every 2-3 years around here and much less if it ever absorbs diesel fuel.

A long time ago.....no, a very long time ago, 25+ years...….. I scraped off the OEM grey foam insulation from the inside of my '83 300SD's bonnet. I drove the car several hundreds of thousands of miles, post foam removal, and never had a paint issue on the bonnet, or anywhere else on the car for that matter.

I drove the SD in the Deep Southern States to Texas for many years in this condition. Dead of Summer included. I must conclude that engine heat doesn't bother the bonnet's top paint.

spock505 · #9 03-06-2020, 05:56 PM

Check the bulk head rubber seals with hood, otherwise it can lead to engine fumes entering via heater scoop on otherside.

This is for a 124 when I drive mine without hood insulation, if stationary with blower on it really wafts in.

It creates an indentation into the foam:

Skid Row Joe · #10 03-08-2020, 02:29 PM

Quote:

Originally Posted by spock505

Check the bulk head rubber seals with hood, otherwise it can lead to engine fumes entering via heater scoop on otherside.

This is for a 124 when I drive mine without hood insulation, if stationary with blower on it really wafts in.

It creates an indentation into the foam:

That's good to know. I didn't notice any fumes of any type though. Thanks!