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Discussion Starter #1
Few days ago I noticed a new rattle from underneath the car, only when I start the car cold, and only for a split second...right when the engine engages. Of course the logical thought was something with the muffler.

I took it in to a local shop where I usually do stuff on my cars for brakes and asked him to look at it.

He said it was the heat shield, he took it off.
I said "O.K...what do you mean took it off? Don't we need it?"
He said "nah, we always do it. It gets rusted, it starts to fall off, we take if off. You can replace it, but it's a lot of money".

We never got into the "how much", but since he is not a young kid and he's been around for "quite some time", I believe he knows what he's talking about.

That being said, can anyone shed some light on the following:
What is this for to begin with?
If we can get rid of it so easily (and I read in other posts that I am not the first one), why do we have it in the first place?
What damage, if any, can be caused by the lack of a heat shield?

Thanks.
 

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04 Accord V6 6spd
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I'm not entirely positive on this, but besides whatever protection it offers the outside i think its supposed to keep heat up the cats quicker and keep them hot. They're useless cold.. i guess lower emissions? anyway; ive been driving without my shield on the front one for a long time now and it has been fine so i dont know
 

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Funny, I just pulled mine off a few weeks ago.

The sheild is about $30 to replace, but you have to remove a few small heavily rusted bolts. Good luck with that! So I left mine alone.

FYI - Its not there for any reason other the protecting the area above the CAT from over heating and starting a fire. But the air gap is very large, you would need some crazy conditions for the CAT to start a heat induced fire.

So I feel fine leaving it removed. And having done this to nearly every car I've owned...I'm not worried in the least.
 

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Ken
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My car rattles when cold too, it rattles mostly from ~2000 - 3000 rpm. My first thought was the same as yours "exhaust related". Upon closer inspection it turns out the heat shield was to blame. My previous car had the same issue, it wasn't exactly the heat shield itself that went bad but rather the rusty bolts holding it. New England weather wreaks havoc on anything that can rust. If it CAN rust then it WILL in this region...
 

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Discussion Starter #5
So what's the verdict? :)

How will it start a fire and where - below the cat, like dry leafs, grass and stuff, or above it between the car. and the car chassis?
 

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Full Throttle
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From what I understand, the main purpose of the heat shield is to protect things underneath the cat. Leaves, plastic bags, etc. Honda's are notorious for having rusty heat shields. Just rip it off and forget about it . . . . and don't park on a bunch of leaves which probably isn't a great idea anyway!
 

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Discussion Starter #8
OK, I'll do my best, although it'll be hard especially now with the foliage coming :D

I am curious though - what is made of? If the cat. produces so much heat that it can literally ignite a fire if it touches dry leafs or a plastic bag, then this heat shield has got to be something other than just a piece of metal, isn't it?
 

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Just cheap steel, don't over analyze it, takes far less temperature to ignite a piece of paper, a dried leaf, or plastic bag then it is to do anything to a piece of sheet metal, even if it's cheap steel.
 

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Discussion Starter #10
Just cheap steel, don't over analyze it, takes far less temperature to ignite a piece of paper, a dried leaf, or plastic bag then it is to do anything to a piece of sheet metal, even if it's cheap steel.
Of course it is, but it if it's just a cheap piece of sheet metal, how does it protect from extensive heat?!
 

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Ken
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Personally I think "heat shield" is a misnomer. If anything it's much more of an insulator. We can compare the heat shield to a winter jacket and the car's exhaust to your body. When you wear a jacket out on a cold day the air around you doesn't get warm but inside you're jacket it's still warm. This is because of the heat that's escaping from your body (which stays trapped in the jacket). Except in a car, hot gasses radiate from the exhaust and stays trapped behind the heat shield.

There's actually a decent amount of info on the web concerning heat, insulation, and shielding if you know how to look.
 

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BRWNFLSH now
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I've heard that you can usually put a couple of those screw type hose clamps (long ones) around the heat shield to stop it from rattling. Mine doesn't rattle yet, so I haven't actually tried it myself.
 

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Of course it is, but it if it's just a cheap piece of sheet metal, how does it protect from extensive heat?!
First of all, which heat shield? Probably the one on the catalytic converter rather than the ones over the mufflers.

Regardless, the "heat shield" serves three purposes:

1. Prevents direct contact of the combustable materials from directly contacting with the super hot catalytic converters which may start a fire.

2. With a layer of air in the space between the heat shield and the catalytic converter, the heat energy transferred froum the catalytic converters to the heat shield is going to be drastically reduced.

3. Metal is an effective thermal absorber/radiator, it will soak up the remaining heat transferred into it and release it as air circulating around it conducts the heat away, further lowering the temperature at this protective plate when combustable material comes into contact with it.

It's just simple physics, or more precisely thermal dynamics.

Now, that's the theory, in reality unless you regularly park over tall dried grass and keep the engine running, the chance of causing a fire is extremely, extremely small.
 

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I've heard that you can usually put a couple of those screw type hose clamps (long ones) around the heat shield to stop it from rattling. Mine doesn't rattle yet, so I haven't actually tried it myself.
I have tried all that and it does not work and is not worth the hassle.

Mine fell off a few years ago and I have had zero issues because of it.
 

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Yep, hose clamps would not work. UNLESS you buy a huge one and wrap it around the body of the CAT and shields. That could work if you dont want to remove it.

The shield is two parts, upper and lower. In most cases this shield is spot welded around the CAT and leaves a 1/8"-1/4" air gap. Honda bolts their CAT shield on.

And I was wrong about the $30 price. It is actually twice that because Honda sells them separately! So $60-80 to replace yourself cause you'd need new bolts provided you can get the old ones out!

Also not, this is the primary shield that surrounds the CAT. There is a secondary (Honda calls it a "floor heat shield") above the CAT that is attached to the car underbody. Removing the CAT shield doesn’t leave us naked exactly, but it does leave the CAT more exposed. So dont park on that dry pile of leaves anymore.

The next thing that typically goes is the flex pipe. Thats a cool $282.
 

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Discussion Starter #16
Thanks everyone.
 

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First of all, which heat shield? Probably the one on the catalytic converter rather than the ones over the mufflers.

Regardless, the "heat shield" serves three purposes:

1. Prevents direct contact of the combustable materials from directly contacting with the super hot catalytic converters which may start a fire.

2. With a layer of air in the space between the heat shield and the catalytic converter, the heat energy transferred froum the catalytic converters to the heat shield is going to be drastically reduced.

3. Metal is an effective thermal absorber/radiator, it will soak up the remaining heat transferred into it and release it as air circulating around it conducts the heat away, further lowering the temperature at this protective plate when combustable material comes into contact with it.

It's just simple physics, or more precisely thermal dynamics.

Now, that's the theory, in reality unless you regularly park over tall dried grass and keep the engine running, the chance of causing a fire is extremely, extremely small.
Now you tell me...after all these years of avoiding those fields that call out to be parked in:lmao:
 

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I'm having the same rattle. I have an 2005 V6. The rattle happens from 1,500 rpm to 1,950 rpm in the lower gears (1-3)

I've tracked down the noise to the heat shield on the cat on the front of the engine. The cat has two heat shields, one on the top side, and one on the bottom. Putting pressure on the top side stops the noise. I may try to get in there and tighten up the bolts - though they are rusted pretty bad.

If that doesn't work I may just take the shield off.
The cats are at 130K miles, so I may have to replace them at some point in the future. Not sure I want to spend $100 now for new shields - plus it looks like it's not all that easy to work in this area.
 

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I'm having the same rattle. I have an 2005 V6. The rattle happens from 1,500 rpm to 1,950 rpm in the lower gears (1-3)

I've tracked down the noise to the heat shield on the cat on the front of the engine. The cat has two heat shields, one on the top side, and one on the bottom. Putting pressure on the top side stops the noise. I may try to get in there and tighten up the bolts - though they are rusted pretty bad.

If that doesn't work I may just take the shield off.
The cats are at 130K miles, so I may have to replace them at some point in the future. Not sure I want to spend $100 now for new shields - plus it looks like it's not all that easy to work in this area.
As long as you have no misfires or oil burning that cat could easily last 1,000,000 miles, cats don't die they are killed. Find something to wrap around the heat shields.

 

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As long as you have no misfires or oil burning that cat could easily last 1,000,000 miles, cats don't die they are killed. Find something to wrap around the heat shields.
Thanks - good to know. I will try to tighten them up with one of those big hose clamps then.
If that doesnt work then I will either remove the culprit shield or attempt to replace it (as long as the price is reasonable).
 
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