teddonahue

I have almost completed a full overhaul of my engine, suspension, undercarriage, trim and interior on my 32 year old 240D Sedan........

However, the engine STILL is making a lot of racket when it is idling and/or cool before it warms up....even then, you can hear this car coming a mile away.....I have installed a brand new heat shield/noise muffler under the hood of the car....installed an engine shock absorber unit to minimize the rattling of the engine when running.

After all of this....it STILL makes more noise than I imagine it did when it came out of the showroom back in 1982....does anybody have any bright ideas on areas or parts of the car that could be fixed/replaced to bring down the level of engine noise? Thanks.

hamrt

Posting a video with decent sound may help.

Plutoe

Welcome the noise--that's the clatter you hear of the mechanical repeat mechanical injection pump opening and closing the individual cylinder delivery valves---the good news is that as rpm increases that idle clatter harmonically goes away, but hopefully the opening and closing continues!!

If you dislike the noise--sell the car and purchase a W211 diesel

hamrt

Well, that's not quite accurate.

Compared to a gasoline engine where the fuel/air mixture is drawn into the cylinder and has a single point of ignition that spreads resulting in a slow, controlled burn and gradual increase in cylinder pressure, a diesel engine draws in air only and injects fuel that burns all at once resulting in a rapid increase in cylinder pressure and a knocking sound. Mercedes diesel engines use an indirect injection prechamber design. The flow of gases in and out of the prechamber tends to increase the noise the engine makes at idle.

The prechamber is located in the cylinder head and is connected to the engine cylinder by small holes. During the compression stroke, air from the main cylinder enters the prechamber. Fuel is injected into the prechamber and combustion begins. Pressure increases rapidly and the fuel droplets are forced through the small holes into the main cylinder, resulting in a very good mix of the fuel and air. As the droplets atomize, they are ignited by the high temperatures created in the cylinder by the compression stroke of the piston and burn all at once and rapidly increase the pressure in the cylinder.

It is normal for the engine to make more noise when cold, and at idle, but it should quiet down as the engine warms up. The clatter should be even and consistent. If one cylinder seems excessive or weak, you may have a problem with an injector or a problem in the pump itself. An out of synch knock could also be caused by a mechanical failure in the engine or simply a valve out of adjustment. The injection pump and injectors should not make enough noise to be heard over the burning of the fuel in the engine. These older, mechanical single injection prechambered engines make a lot more noise than today's modern electronically injected engines that use multiple spays per stroke and no prechambers.