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  #1  
Old 11-18-2016, 06:21 PM
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"Cigar" shaped fuel return line

Happy Friday!

Just performed a diesel purge and noticed upon reconnecting my return line (the one going to the tank that's shaped like a cigar) had a few small cracks near the clamps. In a pinch, I cut a length of 5/16ths fuel line that I had on hand for the purge and replaced it. Amateurish question I realize, but are the parts fungible? Is there any reason for the larger diameter of the original return line? Does it matter?

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  #2  
Old 11-18-2016, 06:32 PM
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i had a normal hose on mine when i bought the car, swapped in the cigar hose a few months in - can't tell the difference. i occasionally had the surging idle when cold with the old hose, and i still occasionally have it with the new hose.
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  #3  
Old 11-18-2016, 06:33 PM
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If it feels and runs the same while driving then I'd go with it. All it does is absorb fuel pulsing that might be felt through the hard lines. Many go with a plain hose, especially if they run biodiesel since as far as I know nobody makes one that's officially compatible.

If you search long enough you'll read doom-and-gloom stories about it, stories about how it was for "dainty" Americans who didn't like vibrations (ever ridden in an American car of the time? Ha!), that it controls the idle, whatever. Haven't heard anyone say it made much difference without it.

-Rog
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Old 11-18-2016, 06:38 PM
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I figured it might have had something to do with a sudden pulse of fuel. Feels the same though, and at 1.60 a foot is a hell of a lot cheaper to replace.
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Old 11-18-2016, 11:03 PM
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Only one case that I know of stands out. So basically if there are no observable differences over a little time it is probably in most cases workable.

An assumption is the more the relief valve is open perhaps the more dampening of the fuel pressure pulses are moderated.

The one case is worth quoting because it was so pronounced. The car ran bad above a certain fuel level in the tank I think. It was suggested over lots of objection that he put the cigar hose in as someone had removed it prior to his ownership I believe. It stopped the problem when installed anyways. Yet I do not remember another single case of this. There have been many cigar hoses removed from many cars.

I believe the original resistance to installing it again was the thought it only reduced noise. This thought had persisted for a very long time and might also still be a factor. Personally I believe it may just have a little more function than that. Enough to notice in most cases it seems not though. Most of them are also very old now and the rubber especially in the south may be Much harder than when newer as well.

Last edited by barry12345; 11-18-2016 at 11:14 PM.
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Old 11-19-2016, 07:10 AM
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times two on noise being the original purpose. It is completely unnecessary on an old clattery diesel.
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Old 11-19-2016, 07:51 AM
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I removed mine on Mutt due to cracking, just like everyone else. No impact regarding the change that I can tell.

Dan
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  #8  
Old 11-19-2016, 10:24 AM
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I replaced mine (along with almost every other hose) not too long after getting my car 3 years ago. I've noticed absolutely no differences.
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  #9  
Old 11-20-2016, 05:04 PM
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Thanks for the insights guys. A $1 hose vs a $16 hose is worth taking a shot on.
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  #10  
Old 11-22-2016, 10:02 AM
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Just a note that the original intent of the cigar hose was to help dampen fuel pulses in the line on turbocharged models. This info was from a former dealer tech (one who worked on these cars when they were current models), who was on one of the forums years ago.

However, that being said, many/most people seem to find it makes no difference.

Every car I have purchased had a regular length of line installed instead. I have put the cigar hose in, as I'd rather know everything is as intended by Herr Mercedes Grando Engineero, if I have to start troubleshooting fuel-related issues. Last time I replaced one I paid $8.
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Old 11-22-2016, 10:06 AM
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An old Mercedes tech told me the cigar hose dampens pulses to protect the metal fuel return line under the car, which could fatigue over time from the pulses. True or not? I am not sure.
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  #12  
Old 11-22-2016, 06:09 PM
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I think the only certainty is the injection pump internally produces very strong pulses in operation. The cigar hose obviously moderates them when the relief valve is open. With the fuel supply at proper pressure the relief valve would always be open. That's if the lift pump is strong and the fuel filters not too obstructed.

Also when replacing the cigar hose with normal hose try to get a piece of clear hose in there as it can aid troubleshooting down the road. Remember as well that information from Mercedes may not be all that good. They neither designed or produced that fuel system.

Many European versions where produced without a cigar hose. The injection pump may be different on them but fundamentally operates the same. As a really wild guess I wonder if those pulses might transit the return system and somehow have a small effect on the injectors. I guess that would depend on their peak pressure. The pulses are of extremely short duration and cannot accumulate base pressure it seems. More like a very high frequency hammering as revolutions build up.
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Old 11-22-2016, 06:27 PM
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The cigar hose was found on both NA and Turbo models. It was to prevent metal fatigue in the metal lines as was mentioned.
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  #14  
Old 11-23-2016, 11:47 AM
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Most of the euro cars I've seen had it, it's $16 and they go bad about once a lifetime. I just replace them with the proper part.
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  #15  
Old 11-23-2016, 12:39 PM
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Quote:
Originally Posted by DieselPaul View Post
Most of the euro cars I've seen had it, it's $16 and they go bad about once a lifetime. I just replace them with the proper part.

Ya I agree, just put it on and move on.
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