Proper Fuel Hose Inner Diameter - PeachParts Mercedes-Benz Forum

903hblue · #1 01-11-2018, 10:59 PM

I want to replace my fuel hoses with some of the transparent Tygon type style. With the regular black auto parts store stuff I use 5/16 with a clamp, but it does fit a little loose. If I am using no clamp with the Tygon stuff, should I go down to maybe 1/4 ID? Thanks.

Diseasel300 · #2 01-11-2018, 11:45 PM

Assuming you're talking about the rubber fuel hose to the lift pump and return? Original size is 7mm which is just a hair smaller than 5/16". A lot of people use 5/16, I had bad luck with air ingress when I tried it and ordered the correct 7mm size and have had 0 issues since.

903hblue · #3 01-12-2018, 12:06 AM

Yes, the hose to the lift pump, plus the hose from the IP to the main filter.
I guess 1/4 inch would be ok, since that is only slightly smaller than 7mm.

73220downer · #4 01-12-2018, 12:30 AM

1/4 inch works fine for me.

903hblue · #5 01-12-2018, 12:33 AM

Thank you, I'll go for 1/4.

Diseasel300 · #6 01-12-2018, 09:45 AM

Which car is this on? Is this on the '93? If so, you might want to consider sticking with the correct size hose. The lift pump on the 60x engines moves quite a lot more volume than the one fitted to the 61x engines and it is known for causing vapor bubbles in the fuel when used with smaller diameter hoses (too high of suction pressure will cause vapor bubbles in diesel). It's a controversial subject, but some folks claim that the fuel lines used in the Mercedes were less than that specified by Bosch and marginal to begin with.

903hblue · #7 01-12-2018, 01:13 PM

Thanks for all the info Diseasel! Yes, this is for the 93, the only benz I currently have.
Wow, that's very interesting and makes a lot of sense. Maybe I will get the factory size for the line to the lift pump and do the rest 1/4 inch Tygon.

Diesel911 · #8 01-12-2018, 08:57 PM

On W123s a whole buch of us use 5/16" hose on the fuel inlet. Never had air in the line issues since I used it since 2007. In fact the same hose is on the Car and working fine.

Of course I used clamps.

BillGrissom · #9 01-13-2018, 01:44 PM

Read up on Tygon. I recall that people who tried it for the small injector over-flow hoses found it didn't last a year. Viton is the best alternative for that (instead of M-B woven type), but you won't find Viton large enough. I used Goodyear Barricade (NAPA), stamped "bio-diesel" at the lift pump in my W123. Probably 5/16", but could be 1/4". I used fuel-injection style clamps, though M-B screw ones should work.

rocky raccoon · #10 01-13-2018, 03:09 PM

The real stuff is awfully cheap. Why on earth would you not use it?

JHZR2 · #11 01-12-2022, 03:34 PM

Quote:

Originally Posted by Diseasel300

Which car is this on? Is this on the '93? If so, you might want to consider sticking with the correct size hose. The lift pump on the 60x engines moves quite a lot more volume than the one fitted to the 61x engines and it is known for causing vapor bubbles in the fuel when used with smaller diameter hoses (too high of suction pressure will cause vapor bubbles in diesel). It's a controversial subject, but some folks claim that the fuel lines used in the Mercedes were less than that specified by Bosch and marginal to begin with.

Is 7mm correct for the 93? I’m likely picking up a W140 from a bit of a distance (100ish miles) and want to bring some spare filters and hose. I am aware of the 7mm hose for my 616/617 engines, but haven’t had to mess with hose on my 603 engines yet.

Are the same hose diameters that are used on the 617 cars correct for the 603, and particularly the later W140 603? I’d be curious about the lines that connect the prefilter and the hard lines, as well as the lines that go between the injectors…

Thanks!!

vwnate1 · #12 01-13-2022, 12:13 PM

Can't you google / Amazon /E-Bay the correct size in Metric ? .

I don't know of there's clear metric hose out there but it's definitely worth looking for .

1/4" is too small I.D. .

BillGrissom · #13 01-13-2022, 08:15 PM

Not sure, but I suspect the clear fuel hose that M-B used is nylon. Many rubbers and plastics don't stand up to diesel, and especially bio-diesel. I saw where one guy used PEX plastic tubing (Home Depot), but it is stiff. As I stated, 5/16" ID hose fit for me (=7.9 mmID). I used Goodyear Barricade, which I think has a Viton liner (hence the name).

Diesel911 · #14 01-13-2022, 10:15 PM

Quote:

Originally Posted by BillGrissom

Not sure, but I suspect the clear fuel hose that M-B used is nylon. Many rubbers and plastics don't stand up to diesel, and especially bio-diesel. I saw where one guy used PEX plastic tubing (Home Depot), but it is stiff. As I stated, 5/16" ID hose fit for me (=7.9 mmID). I used Goodyear Barricade, which I think has a Viton liner (hence the name).

If I remember the GoodYear Viton linings are blue, and the Gates Viton linings are Brown.