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  #1  
Old 01-11-2018, 10:59 PM
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Proper Fuel Hose Inner Diameter

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.
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  #2  
Old 01-11-2018, 11:45 PM
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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.
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  #3  
Old 01-12-2018, 12:06 AM
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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.
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1982 240d (sold) - Igor
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  #4  
Old 01-12-2018, 12:30 AM
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1/4 inch works fine for me.
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  #5  
Old 01-12-2018, 12:33 AM
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Thank you, I'll go for 1/4.
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Last edited by 903hblue; 01-12-2018 at 12:34 PM.
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  #6  
Old 01-12-2018, 09:45 AM
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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.
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'86 300SDL - "The Diseasel" 180K
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
Delivery Valve as Source of Nailing Thread
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  #7  
Old 01-12-2018, 01:13 PM
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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.
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1982 240d (sold) - Igor
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  #8  
Old 01-12-2018, 08:57 PM
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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.
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  #9  
Old 01-13-2018, 01:44 PM
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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.
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  #10  
Old 01-13-2018, 03:09 PM
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The real stuff is awfully cheap. Why on earth would you not use it?
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