How to stop rattling in car?
November 15, 2011 8:27 AM   Subscribe

Rattling muffler/exhaust?

12 yr old civic - hear a rattling coming from the back so I assume it's the muffler/exhaust. The rattling is continuous when driving, but if I put it in neutral, it quiets down or goes silent. Does anyone know what's wrong with my car and how to fix it?
posted by grak88 to Travel & Transportation (14 answers total)
It could be as simple as needing a new exhaust hanger. The reason it doesn't rattle in neutral is because it's not under load.
posted by Burhanistan at 8:30 AM on November 15, 2011 [1 favorite]

I would go with loose heat shield.
posted by sanka at 8:35 AM on November 15, 2011

The exhaust in that era Civic seems to be one of the few things that needs work from time to time. Could well be a hanger -- especially if it looks like it's hanging lower than it should at the back -- or it could be the resonator or heat shield, but those rattles are usually from slightly further up front. It's not going to be an expensive fix, either way.
posted by holgate at 8:36 AM on November 15, 2011

You have either an internal baffle in the exhaust loose, a heat shield has cracked and is rattling (around the exhaust usually) or a hanger rubber has broken on the exhaust itself and it is touching the exhaust when it is loaded or vice versa.

Take it to an exhaust shop or get underneath the car and start wiggling things (when they're not hot). Those are your only two options, really. It's unlikely to be major but could be a fix for a zip tie/piece of wire up to a new exhaust section.
posted by Brockles at 9:10 AM on November 15, 2011

I'd say a loose catalytic converter heat shield is most likely, although that's not really in the back so much as under and in the middle. It's a little tricky to get to it, since it's located in the middle of the car just behind the engine between the floor pans (slightly ahead and down from the stereo, if that helps). The converter is the odd bulgy part in the exhaust pipe just downstream from the exhaust manifold. (Not to be confused with the resonator, which is the much longer bulgy part under the mid-section of the car and probably doesn't have a heat shield.) The heat shield is a piece of sheet metal that sits on top of the converter; it's usually tack-welded in place. If the heat shield feels loose, wrap a bit of bailing wire around it and tighten it down. (I can suggest this, because I have done it.)
Just before the muffler on my 16 yr old Civic rusted through and broke loose from the mid-section, it sagged enough that the tail pipe rattled up against the underside of the rear bumper, making a horrible racket. In this case, the fix was 'replace decayed muffler', which was about $100 in parts and a messy evening under the back end of the car cursing and cutting my hands up on the rusty bits of exhaust.
Most of the time, this sort of odd rattling coming from the exhaust can be repaired by locating the offending bit and wrapping bailing wire around something to hold it in place. I wouldn't recommend zip ties because most of the exhaust gets hot enough to melt them.
posted by leapfrog at 1:49 PM on November 15, 2011

Pretty much all the advice is good in this thread so far.

I had rattly heat shields removed on three consecutive cars I owned (81 Honda Civic wagon, 87 Subaru GL, 96 Honda Civic), so I assume it's common for others too and is therefore what I would check first. Also, the rubber hanger things on my old Subaru came off a couple times to cause a similar rattle as well. Assuming an honest mechanic, shouldn't be expensive to fix.
posted by aught at 2:06 PM on November 15, 2011

Is is ok to remove a heat shield? I mean, isn't it shielding heat for a reason?
posted by grak88 at 2:36 PM on November 15, 2011

Don't remove the heat shield, but you may be able to Heath Robinson some alternative method to hold it in position a bit longer - eventually you'll need to replace it, but you may be able to prolong the inevitable (and stop it rattling in the meantime).
posted by Brockles at 2:49 PM on November 15, 2011

Is is ok to remove a heat shield?

It's pretty much fine to remove. If you were going to park your car on top of some dry brush, I guess you could start a fire. But in general they fall off cars that are 10+ years old and no one misses them.
posted by knave at 3:19 PM on November 15, 2011

Heat shields are usually between the exhaust and the vehicle itself, rather than between the car and the floor (except the ones undeneath catalytic converters). As cars get old and oil gets caked into the accumulation of dirt underneath a car (so between the exhaust and the car), they can be more important than when they were new (again especially around catalytic converters). However, some of them don't do much except in the harshest conditions.

So, there is a relatively high chance that someone who knows what they are doing could take one or two of the several heat shields out and it never matter one bit. However, because you freely admit you don't know what you're doing and because there is a reasonable to outside chance that the heat shield could matter, I don't think it is wise to give a blanket "It's fine to remove it".
posted by Brockles at 4:57 PM on November 15, 2011

Yes, I'll be the first to admit I have no clue what I'm doing. Thanks for all the help folks!!!
posted by grak88 at 5:20 PM on November 15, 2011

Heat shields are generally ok to remove (in my experience), but watch out if you remove any from the exhaust headers under the engine. There are plastic and rubber parts near that area like CV boots that can melt and cause bigger problems.
posted by PSB at 5:36 AM on November 16, 2011

There are three ways to fix a rattling heat shield: tack weld it back down (the standard shop approach, which is great if you have a MIG welder handy), tie it down with bailing wire (standard backyard mechanic approach, works great except eventually the wire will get loose again due to expansion/contraction cycles and rust), or remove and discard the heat shield. Whether or not the heat shield can safely be discarded is largely a question of which sensitive part it is shielding from which source of heat. Parts farther back will be significantly less hot. The exhaust manifold (connected to the engine) and the catalytic converter (connected to the exhaust manifold) are going to be the hottest parts, and also closest to things that could be damaged. I wouldn't remove the shields on those. Anything further back, I'd likely toss if it proved difficult to wire down.
If you're set on fixing it yourself, just get underneath the car when it's cold and start wiggling exhaust parts from the tailpipe back. Most of it will move a little bit; it's designed that way. When you find a part that seems really loose or that you can readily bang against something else, grab some galvanized wire and go to town. There is a chance that it's actually something inside the muffler come loose and started rattling, which means it's time to replace a muffler.
Otherwise, take it to the shop and explain "something is rattling in the exhaust, I just want it bailed up or tacked down". If their estimate is more than $30, ask for a detailed writeup and take it to another shop to confirm before you commit to anything.
posted by leapfrog at 6:43 AM on November 16, 2011 [1 favorite]

The exact same thing happened to our similarly aged civic a few months ago. Heat shield all the way.

I threw a larger hose-clamp around it, because the actual mounting bracket was broken. I thought it would need to be welded down.

I had completely forgotten about it, when we took the car in for it's regularly scheduled check-up. The mechanic (that we trust, very much) said that's exactly what they would have done for it. Just a big, hose clamp.
posted by furnace.heart at 1:18 PM on November 16, 2011

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