Initially the lines were filled with air and droplets of fuel dancing around inside with every injection cycle. After 100+ miles all the tygon lines are filled with fuel. I can't see any air bubbles inside.

I'm worried about the low temp rating (165f) of the tygon especially on the om606 where they're covered up so I picked up some viton hose just in case. I'm going to keep an eye on them. So far the injector Wells are dry.

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CENSORED due to not family friendly words

I'd keep an eye on them. I had these neon green/yellow return lines a few years ago and one blew off spilled fuel all over made a mess. Being low temp and soft in durometer, these so called Tygon lines gets softer with increase in temp and can't handle much pressure. Make sure the tank vent is working. My estimate is they can't handle anything more than a few psi's. Injector return lines should be hard to pull off the barbs once installed. Not these, they are so soft a slight yank pulls them off.

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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

I have two specific questions to add to this thread.

1. If going with Viton, should the firm (Durometer 75A) or soft (Durometer 60A) be used?

2. Anyone have experience with Tygon running B99? I'm leaning toward Viton, both because of the B99 uncertainty and also because I find funola's argument about increasing softness with temperature and possibility of high tank pressure compelling.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"

Those fuel return lines really do handle a lot of fuel. At idle it is not so much, but on driving from Indy to Philly and return last month, I was running it pretty hard just before the toll road and I lost that little rivet like piece that sits in the cloth covered tube behind the last injector. Well at 75 mph that plug came out and you leave a cloud of diesel vapor over the interstate. I bet a lot of drivers moaned about that, though traffic was pretty light. But in the 5 to 6 miles to the next exit I like I probably dumped 5 gallons of diesel. Took a screw out of the license plate and screwed that in and it held it until I returned home. Outside of that and a quart of oil at 700 miles running 70/75 and just a little above normal on temperature and it was hot, but a good ride. I enjoy that 240D with the 617 turbo and a four speed stick very much.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Yes, I too had to make a "side of the road" repair, pulled into a parking lot and noticed a trail of veggie oil behind the car and a puddle forming under the engine. For me too the culprit was the last bit of tubing near the firewall, although in my case it was caused by a gaping hole in the tubing just above the nipple. So I cut that piece shorter and pushed it back on and it has been holding fine, but it's time to replace all that hose.

I reckon the B99 I just started running was the last straw for that old return line.

All I need to know, really, is whether to get the Firm or Soft 1/8'' i.d. Viton. I haven't been able to find that info yet. I suspect they both work but that one lasts longer.

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1984 300D Turbo 350K 50K WVO (two tank) "Maeby"

11.28.2018

TTT .

? What's the current situation after two years ? . still happy or needed replacing .

There are several grades of the woven made in Germany return hose, the gray stuff is what Mercedes uses/sells/recommends and it lasts longer than three years with Bio Diesel as well is Dino Diesel .

I keep spare hose in the car along with a spare end bullet piece just in case as I too lost one once on a road trip .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I had to replace mine after about 5 years of service. They were hard around the hose barbs on the injectors and leaking a little bit.

I ended up getting a different type of hose this time around.


McMaster-Carr part number 5792K32.

Abrasion-Resistant Polyurethane Tubing for Fuels, 1/8" ID, 1/4" OD

https://www.mcmaster.com/5792k32

Attached Thumbnails

 

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

^ That blue poly tubing is what I've been running as well. Absolutely no leaks and it's cheap.

-Rog

? For how long now ? .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Blue vs yellow debate? I'll buy both, and split it up on half of the engine. By the way what plug do you guys use?

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

I guess I should update on this, the tygon failed after just a few weeks on the om606. Switched to neoprene never looked back.

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CENSORED due to not family friendly words

I've been running the blue tubing for a little over 2 years.

-Rog

No matter what you use carry some extra in the Trunk.

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84 300D, 82 Volvo 244Gl Diesel

I have a 1500 foot roll of nylon braided Viton that I had custom made. PM me if you want some.

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.

Since this popped up again, I'll update. The Viton tube on my 1985 is still fine several years later. My son had the 1984 home recently and I saw all the cloth-covered "Made in Germany" injector hoses were wet and dripping a bit on the engine. I changed all to Viton, except used cloth for the long one to the fuel filter since I had a whole roll to use up and that one is easy to change later.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans