Purpose of hood insulation pad


New member
My 2004 Sprinter 2500 is missing the hood insulation pad. Before I get a replacement, I wanted to know what its purpose is. Is it for sound, thermal, both, something else? Please share your thoughts.


2015 RT SS Agile (3.0L)
My thoughts: As far as I know, all diesels --"soft" diesels, at least; no experience with OTR trucks-- have them. I believe mostly for sound attenuation, though in cold weather operation they help with thermal retention as well. My '82 Peugeot 504D Estate, my 2005 Jetta TDI Wagon, and our Sprinter all had/have heavy under-hood & firewall insulation.


Active member
I believe every auto I have ever owned has good insulation. Pretty sure it provides thermal protection to good and noise absorption. Experiment to show what it does to reduce sound level: put a buzzer type doorbell in a coffee can and activate. Now line the coffee can with absorbing foam and activate the buzzer. Can only actually amplifies sound.


He’s just this guy, you know?
My understanding is that the hood insulation is there as a fire blanket in case of an engine fire, thermal and sound insulation are secondary

Aqua Puttana

Poly - Thread Finder
My understanding is that the hood insulation is there as a fire blanket in case of an engine fire, thermal and sound insulation are secondary
I've heard that also, but don't know if it is true. There is no reason to protect the metal hood aka bonnet from the fire. It won't burn. One theory I heard is that the insulation falls down to smother the fire. The insulation falling down, assuming that it even will release and fall, given the engine compartment shape/design of a Sprinter I doubt it will fit tight enough to block oxygen and smother a fire.

FWIW. I lean toward sound and perhaps thermal issues.

:2cents: vic


Dis member
I lean towards sound attenuation as the primary purpose. I believe diesel IC is louder in the engine compartment than gasoline IC, so sound attenuation under the hood is even more critical. I remember researching "alternatives" to gasoline IC in the 1980s, and diesel was being promoted but with the caveat that it required more sound attenuation to make it acceptable to consumers.

Here is a Reddit discussion (if you want to get an Internet expert opinion): https://www.reddit.com/r/explainlikeimfive/comments/6k859b and this ResearchGate: https://www.researchgate.net/post/Why_do_diesel_engines_produce_more_noise_than_petrol_engines


New member
Thanks all! You gave me 3 good reasons to purchase a new pad. I don't know the order of importance of the 3, but for $70, I don't need to over-think it.


Former Nelson BC Sprinter
1: in a engine top fire the plastic clips melt and pad falls on top of fire, put my car fire out in 15 seconds
2. Protects hood paint from engine heat
3. Reduces engine noise levels
4. Provides a home for mice and small birds


2015 RT SS Agile (3.0L)
Ha-ha.. absolutely! Forgot about "#4"!!

Due to parking outside, both my Peugeot and my VW have had -- in the past -- infestations of mice. They went other places too, but in both cases they went for the under-hood insulation. Tough call; there's a thread on this forum about ridding our vehicles of creatures -- give it a read. To get rid of them? It can be easy... or it can be hard.

Keep my VW in a garage now, so no further issues, and --so far-- our Sprinter has only had paper wasps move in to voids around the front doors while it's been parked outside for extended periods. (My 504D died some years ago...)
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the dude

Maybe the hood insulation is the reason for my " black " hood to be repainted now ,,,,, 6 times . 2014 -144 WB -I-4 . The MB specified paint shop said , " this maybe an annual repaint " . MB & the paint supplier are paying .
A layer of bedliner on the topside of the engine hood also acts as a great sound deadener besides the never rust again, never have any rock damage again factor.

Diesels deserve to be muffled in any way we can and with the lackluster MB paint jobs on these 'work vehicles' which is no excuse, sealing the paint is recommended in any way we can.

Keeping mice from setting up shop in the padded insulation takes its own precautions like fragrant dryer sheets, ultrasonic sound units, not so sure about this one, hot pepper, capsacian impregnated electrical type of tape available at Honda dealers or online, lights at night in the engine compartment.

Many have tried many things to repel rodents and the damage they can do. To protect wiring specifically, the hot pepper tape works. It would be fun to see a video of a mouse first trying to chew through this tape. If this could be applied to the padded insulation somehow it could work there too. Maybe underneath the insulation?

Aqua Puttana

Poly - Thread Finder

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