Is a (under-bonnet) sound-deadening mat necessary?

[Brigadier]

For a diesel?

Just wondering, as mine tore when I was faffing with the washer jets.

I've repaired it - after a fashion - but was just curious as to how essential they are.

 

[Burnerman]

As they say......every little helps but you won’t notice much difference inside the car. Many engines have an acoustic hood too, and an undershield.
What you don’t want of course is for any pieces to fall onto the alternator belt!
John

 

[Deluks]

Reduces condensation build up on the underside? And potential protection from errant stone chips?

 

[JohnD]

It helps a bit, but I find it difficult to fix a new one. There are some heat-resistant adhesives but you probably need to take the bonnet off and turn it upside down while it sets.

 

[Avocet]

Generally only there to help get through the type approval noise tests. You can remove it, if you're not bothered by a bit of extra mechanical noise outside the car.

 

[Mottie]

but was just curious as to how essential they are.

Essential if you have a keen-eyed mot tester as they are part of the mot these days. If it’s missing, it’s a fail.

You can remove it, if you're not bothered by a bit of extra mechanical noise outside the car.

You can't. Not without the possibility of a fail, come the next mot.

 

[Brigadier]

It helps a bit, but I find it difficult to fix a new one. There are some heat-resistant adhesives but you probably need to take the bonnet off and turn it upside down while it sets.

It was fixed on with fasteners (like big, nylon, drawing pins).
But I tore one of the edges, trying to get the fastener out.

I tried contact adhesive on the ripped edge, in the hope that it would go tacky and I could stick some ripstop fabric over the damaged bit.
Whether the adhesive was past its sell-by or whatever, but it just wouldn't stick at all.

I ended up using an office stapler to fix the patch instead.

 

[JohnD]

I keep a box of assorted trim clips and fasteners. They tend to wear out or break. You can get trim removing pliers quite cheaply, mine are like a reverse plier with two thin folks that you slide under the head. When you squeeze the grips the two forks push apart.

Underbonner parts tend to be dirty or oily so glues may not work unless pre-cleaned.

 

[Burnerman]

Essential if you have a keen-eyed mot tester as they are part of the mot these days. If it’s missing, it’s a fail.



You can't. Not without the possibility of a fail, come the next mot.

Seriously......an MOT fail? That's a new one on me!
Cheers Mottie
John

 

[Mottie]

Seriously......an MOT fail? That's a new one on me!
Cheers Mottie
John

 

[Burnerman]

Well well well.......considering how 'soft' the MOT test is in some areas, I'm quite shocked by this!
John

 

[Brigadier]

View attachment 331971

Reading that then, if I took the mat off and stuck it in the boot, that would not be a fail because:

- it was available to be inspected, and
- it was not insecure

 

[Avocet]

Essential if you have a keen-eyed mot tester as they are part of the mot these days. If it’s missing, it’s a fail.



You can't. Not without the possibility of a fail, come the next mot.

Blimey! Really? They make very little difference and a car with one removed, would still be well within minimum noise requirements under UK legislation!

 

[Mottie]

Reading that then, if I took the mat off and stuck it in the boot, that would not be a fail because:

- it was available to be inspected, and
- it was not insecure

Probably. Unless the tester can say that it is standard on that vehicle. You can do that with lights, windscreens and seats. Then the screen, wipers, washers, seat belts, lights cannot be tested - or failed!

 

[Avocet]

That's really surprised me! Ordinarily, most things on the MOT are a pretty low bar. Brakes have to be well below par to fail. Emissions too. Silencers can be pretty noisy before they fail the subjective noise test. The idea that I could fit a cherry bomb silencer in place of my back box, and (probably) still pass the subjective noise test, but if it even looked like my underbonnet sound deadening pad might fall off, it should fail, is nuts! In reality, he'd never be able to hear the difference if I DID take the sound deadening off, but would definitely hear if I took one silencer out.

And then the icing on the cake, is that "insecure" and "likely to become detached" are "major" and "dangerous", respectively?! I am genuinely gobsmacked....

However, it doesn't say:

"insecure,
likely to become detached,
missing altogether"...

Anyway, I've just decided. That furry stuff under my bonnet, is a heat insulation pad, it's nothing to do with sound deadening...