Hi,

Quick question regarding the fuel pump on an 83 300D. How dangerous is it to run the fuel down really low in the tank? In my 98 chevy truck I have heard that the fuel pump utilizes a return stream for cooling of the parts of the fuel pump, and thus they give a 5 gallon reserve, so that the fuel light comes on at that amount to protect the fuel pump. I dont knwo how a diesel pump works, so Id liek to know. Does it use a return fuel stream to cool the diesel pump? I have heard that people who let the chevys go way low often have charred wires or burnt out fuel pumps. I dont want to have that happen to any car of mine, so I just want to make sure if it is an issue. Id get gas at 1/4 tank anyhow, but just want to be sure. Thanks

JMH

I think it safe to say that you have nothing to worry about from merely running rather low on fuel, because all the pre-chamber type M-B Diesels that I know about rely entirely on the injection pump to pump the fuel -- there isn't any pump back there in or near the tank. Some newer common-rail and TDI type Diesel injection systems do have a separate fuel pump (and computer controls), though, just like gasoline injection systems.

Running completely OUT of fuel, on the other hand, can deprive your injection pump of needed lubrication for a few seconds, until the motor stalls and coasts to a stop, and will require you to prime the pump by hand for what seems like an eternity before you get restarted.

The fuel pump in the later Chevy trucks is an electric pump which could run long after the engine stops for lack of fuel. Therefore it is possible for it to be let it be damaged by running it dry. Let it up to Chevy to put in something that can be damaged.

The fuel pump in MB Diesels (except for the CDIs) is a mechanical pump driven off the injection pump and will not will be damaged by running out of fuel because when the engine stops the fuel pump stops.

P E H

Many (perhaps most) of the Bosch and Bosch-licensed gasoline injection systems built since about 1980 have the pump or at least the "pre-pump" (SAAB's term) or transfer pump immersed in the fuel for cooling. I believe that the trend started with the Porsche 928 or 924 in the mid-70s.