The topic is noise deadening

[jettaman8691]

First, the specs.
A2 Jetta (can't define the year because it is a collection of several years of A2's), 1.6 TD, Audi oil cooler, dual radiator fan from a 1995 2.0 Jetta, no air conditioning.
I get around 46-48 mpg, depending on how hard I drive it; usually around 65-72 mph. Would like to get into the 50's mpg, at least, but figure what I now get isn't too bad, especially considering I carry a toolbox and such (about 100#) in the trunk all the time. Poor old shocks are needing a pick-me-up.
I have experimented with putting air conditioning duct insulation (from Home Depot, the kind with the tin foil backing) on the floor and doors. It seems to help a bit. I put a different headliner in, that has a kind of padded feel to it, and that helped. But the vibration and noise from the engine and drive train is still too loud.
Has anyone here ever used an engine blanket, such as you might find on large truck cowlings? I understand that to get silence it takes mass, which can be heavy, and impact the fuel efficiency, but in this day, there has to be other options to help get control of the noise of these old diesels, other than upgrading to a TDI.
What say y'all?

[mattbondy]

Reducing the volume of lower frequencies requires more mass. From my experience (I had a slushbox) the noise of the engine only really became a problem at high engine speeds and the frequencies of concern were not too low. I have only heard of requiring heavy insulation for really low frequencies. I suspect these cars might not have much sound insulation since they are not high end vehicles.

[zman]

It sounds like something is wrong. I think you have a bad front motor mount, thats the one closest to the cam gear. When that one goes your dash will vibrate and basically your sheet metal will act as a big metal speaker transmiting all the noise and vibes into your interior.
I have a stock 79` its not bad at all, not like your describing.

[82vdub]

As Zman said, motor mounts could be a fairly significant issue with cabin noise. If you haven't changed those, they may cause a lot of what you hear. I had an intake manifold come loose and before I figured that out, the car was very loud. Also, the clips that held the front of the air cleaner to the intake manifold had over the 350k miles eaten away at the aluminum. I removed all 4 clips and installed long hose clamps around the air cleaner to securly fasten that to the intake. That was a huge noise reducer. Also, if you take the air intake and duct it to outside the engine compartment, this will also reduce noise. Your A2 should have this already, unless it's missing.

[jettaman8691]

What I did was take a '91 Jetta GL 16 valve and put the diesel in it. The air intake is a box jerry-rigged from a gasser and plumed into the turbo intake. What I would like to do is take a 16 valve air box and plum that in, instead. It would fit better and look better. Then perhaps insulate the airbox, as a bit of noise does come from that.
The big noise does come when running at higher speeds and rpm's. The motor mounts seem okay; I just changed the one on the right side; the passenger side. The nut stripped on the front mount, so need to replace it.
The exhaust system could definitely use some work. With the rear end riding a little low, occasionally the pipe will rub on the frame, and that is a noise maker, too.
I have been looking at some isolators used in industry to separate machinery from floors, and such. Been thinking that perhaps a bit more separation of metal to metal, where possible, might absorb more vibration and low-frequency noise.
Just tinkering with my rolling hobby/therapy rig. Thanks for the thoughts.

[vixentd]

Although the front engine mount on the gas motor will fit on the diesel it is the wrong one as the diesel takes an hydraulic mount. Makes a world of difference.