Ideas to quiet down a 617 engine?

[dawsonj3]

All,

Let me first say that I love my 300D and I wouldn't change that much about it. That having been said - the engine starts getting loud at 70 mph, and gets louder at speeds above that. It turns around 3500 rpm at 75 - 80 mph, which I think is normal for a 4 speed automatic.

My question is this:

Do any of you have any strategies, suggestions, etc. to quiet down the 300's diesel engine? Are there any sound deadening devices on the market that I could install under the hood or on the firewall?

Thanks.

[Maxbumpo]

I wonder if the baffles in the first muffler have given out - I understand that they do a lot to reduce engine noise.

There should already be a hood pad installed. You can get one from any MB parts reseller.

I know of folks who have installed a sound deadening product called Dynamat and they've been pleased.

http://www.dynamat.com/

I would imagine that if you removed the dash and used this product on the inside of the firewall and under floor covering of the footwells and seats and tunnel, you could achieve significant results, but that would be a lot of work. Would be much easier to buy a 124 or 201 diesel car...

[ds190]

Way back, I installed DynaMat in my father’s 84 300CD. We put it under the removable front and rear carpets, pulled the rear seats and placed it under and up in that body area, and installed the Dynamat hood pad material on the underside of the hood (instead of the MB pad) and on the engine compartment side of the wheel well arches. It was a noticeable difference but it was still a diesel. Dave

[ghoward@goldrus]

Run biodiesel. Diesel noise drops down considerably - almost sounds like a gas engine.

[Marshall Booth]

Run biodiesel. Diesel noise drops down considerably - almost sounds like a gas engine.

Running higher Cetane fuel will reduce engine noise, but raising Cetane lowers energy content (other factors being equal) so fuel economy will drop!

Be sure that the valves are properly adjusted, that the rockers are not damaged, that timing chain stretch is within tolerance and the injection point is properly set.

When were the engine mounts replaced? What about the other rubber isolators along the driveline? The entire engine/drivetrain/exhaust is isolated in rubber from front to back. The rubber parts have about a 10-15 year life. If ALL of them haven't been replaced in the last 10-15 years, the car will be considerably noisier than it was when new!

Marshall

[Donald Holm]

Marshall mentioned motor mounts. This is an excellent place to start looking for wear& tear.
Having been the owner of several 617 propelled MBs.I have found that replacing engine mounts has quieted many of these Diesels.
Many owners look for a more serious, or complicated problem, but IMOH motor mounts is the first place I would check.

[cervan]

i just turn my radio to max :D

[tscorda]

styro foam earplug $0.10

[Melvin K lofton]

My 85 300 TD engine can't be heard on huighway below 69 mph - then an engine noise comes in from that speed up. I consider it inherent in these cars, so I set cruise at 69 if I don't want to tolerate the small but noticeable noise. I always keep fresh motor mounts, air cleaner mounts, fresh air cleaner - noise has never changed in the 16 years I've had the car.
85 300 TD 140k
88 300 SE 98k

[Marshall Booth]

The simple way to eliminate the noise from a 617.95 engine is to trade up to a car with a 603.96 engine. The noise from the engine is the same at 50 mph and at 100 mph. The telephone poles DO go by faster though!

Marshall

[dawsonj3]

My 85 300 TD engine can't be heard on huighway below 69 mph - then an engine noise comes in from that speed up. I consider it inherent in these cars, so I set cruise at 69 if I don't want to tolerate the small but noticeable noise. I always keep fresh motor mounts, air cleaner mounts, fresh air cleaner - noise has never changed in the 16 years I've had the car.
85 300 TD 140k
88 300 SE 98k

Yes, the issue is that the engine is quite loud at 3500 RPM ~75-80mph. It is quite tolerable at 65, but the clatter from under the hood really starts kicking in around 70. Perhaps I should consider new injector nozzles after 200K? I have checked and adjusted the valves, and the timing chain stretch is about 1 degree. As for the engine mounts and shocks, I will be replacing them soon as the lower oil cooler line is beginning to drip and thus in need of replacement.

[VLayton]

The sound deadening materials improved throughout production, and places to check also is the tranmission tunnel insulation, and see what is in the dash as well. (didn't see your model listed)

But a thought occurs about the speed relation, it could be tires or an exhaust wearing loose. Add those to you list of possibles.

Cheers

[Boneheaddoctor]

Sure you don't have Injector "nailing". I ask because I have an '83 300D and i have more tire noise than engine noise, up to the 95 mph I have taken it to. I hear the engine far more at idle then while driving when you really have to listen for it. I have no additional sound deadening other than what it had when it left the factory. Car is amazingly almost free of engine noise 50-90 mph. And Thats with the usual crap that passes off as diesel around here.

[mustapha63701]

I have a similar issue with my pair of w123 300TD's and well, this is the thing that works for me (and the difference is very noticeable!) I switch to my w126 560 sel and presto, 'tis quiet time again! :)

All jokes aside, I would check the exhaust system to ensure that it has not been altered. Typically, the exhaust systems can be severely modified by subsequent owners, over many years (original set-up is a bit pricey but comes very close to being efficient) and mufflers intended (in some cases) for gasoline engine vehicles can be somewhat ineffective on our diesel Mercs.

I also agree with the hood pad solution and additional sound deadening materials installation suggestions. Be forewarned however that I would not recommend tearing into the dash assembly, unless you're very familiar with such work and feel very comfortable doing it. You may end up with additional interior noises, etc.

Please keep in mind that the actual "clanging" is the thing that really gives these cars some of their character and well, in my case, I just live with it and have even come to enjoy the clattering.

Best of luck ta ya in your quest for the ultimate, quiet driving machine. :) (Now my old Jaguar Vanden Plas was truly a quiet car...)

Mustapha

[stricht8]

Run biodiesel. Diesel noise drops down considerably - almost sounds like a gas engine.

I have not noticed any decrease in noise level with biodiesel in my 220D. I have noticed a decrease in smoke and an improvement in odor.
Dimitri