On my '85 300d....

Changed all the return lines a month or so ago. I noticed a slight diesel odour on a hot day and found the longest line, the one from the first injector back to the filter head, is sweating for the first 1.5 inches from the injector.

I have never had this happen to a recently replaced return line. Is it an indicator I damaged it on the install, somehow?

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

I'd put two bits on it being the wrong type of tubing, breaking down in the diesel/bio-blends. I can never get parts store guys to grab the right stuff.

Damage would show immediately at the end of the barb, or between the end of the barb and near end of the tube....unlikely to extend that far past the barb.

Just my 2c...

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1985 MBZ 300D (DD, 240k, unmuffled hellion!)
1982 MBZ 300D (372k, retired for parts)
1981 MBZ 300D (575k, parts pig)

It's the standard return line and I run pump diesel only in my cars.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

I seem to recall that the leak off hose was one of those parts I wanted to get from Mercedes, back when I had OM61X engines.

Could yours be a non OE line?

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Could be. I have used whatever I could get over the years and never given a thought to origins. I have purchased at the dealer, from the local specialist parts store, from the auto house in AZ, etc etc.

I never figured it was something to sweat origins on. Good point.

Could also just be old stock I suppose.

I mainly wanted to see if someone would bring up a system issue that might cause it. I just don't want to replace the line and be band-aiding a bigger issue, that's all.

Tks

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

I had this problem when an Indy told me his hose was far superior to the oem return line. I replaced with oem line and never had a problem since. One month seems like when it failed on mine also.

Don't laugh, but maybe the guy who opened the hose reel used a knife or razor blade to cut the packaging and sliced the hose. Happens often.
What colour stripe is on the hose, the easyway to know if its vacuum or fuel use hose.
I have found the hose doesn't last nearly as long as it once did, even the proper stuff. Quality has disappeared in a lot of things. I have to keep some in the car at all time especially the little end plug it sometimes fails suddenly and lets the fuel drain off/returns to the tank but never leaks externally so you know there is a problem.

No stripe at all as far as I can tell. Never recall ever seeing a stripe on stuff purchased from the vendor in Hull.

This last batch I used I must have got online, however, as it was a standard length roll packed in a small baggie.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

probably old stock. just had the same problem. leaking original return line, replaced it with new stuff, leaking in a month, replaced it again and its fine.

hard to tell how old the hose is, could be new old stock been sitting dry cracking for 15 years, and you think its new when you get it. i threw out the 2 meters i had originally. had it for a couple years, no idea how old before that

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what is the point of the cloth covering i sometimes see on the return lines?

i used McMaster-Carr and it worked fine.

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'77 240D, 504H, OM617.952, etc.

The braid covering gives it strength and protection making it a reinforced hose as opposed to a tubing, such as the one you linked to, which will not hold up in the long run in my experience. Most of the tubings available are too soft and can blow off with very low pressure.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked