On my 84 300cd, I replaced the return hose with a straight piece of fuel line, thinking that it was just old and swollen. Found out later that the return hose is supposed to be "swollen" like a banana. Why is that?

I'm surprised that no other diesel heads/engineers have replied with the fact that any time a tube or hose tapers to a larger diameter, it is to lessen back pressure. Return hoses are the cheapest and easiest parts to replace, it is better to do it in your drive than on vacation/holiday.

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When I close my eyes, and inhale, I can smell No. 2.

Give us a picture dieseldan

The "cigar hose" as it is sometimes called is ment to dampen pulsations in the return line. Using a regular piece of hose in its place has been known to produce a rythmic knocking sound as the steel portion of the return line jumps around due to the pressure spikes.

Bob D.
1971 220D
1983 300SD
1984 300SD

Glad I read this, I thought that return line was bad too, and had replacing it on my todo list.

But when it is explained it all makes sense.