GL Class (X166) 2013-2015 after facelift became GLS (X166)

Fuel rail question

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Old Dec 5, 2023 | 08:25 AM
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Dannyboy2375's Avatar
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2001 SL 500
Fuel rail question

Hi everyone 👋

I was wondering if anyone knows the reason behind the oil feed on the fuel rail of any of the m278 vehicles.

We recently did a Injector on a 2013 gl 450 and the seals inside the rail are covered in oil. I see that the valve cover has a hole with a small gasket to allow oil pressure to enter the small galley on the fuel rail.

My question is what is the purpose behind this and what are common symptoms of this system failing.

Thanks!!!!
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Old Dec 5, 2023 | 09:17 AM
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arsupisemnet's Avatar
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2014 GL450, 1992 W140 300SD, 1993 W140 300SE, 1987 E30 Convertible
That is not an oil feed. That is non return leak off fuel line, which then evaporated through crankcase vent
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Old Dec 5, 2023 | 09:27 AM
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2001 SL 500
That makes more sense than oil.

However like I said when I removed the rail and removed the injector from the rail it's was full of oil.

When i say full of oil i mean the top of the injector was covered and that small passage was completely full of oil as well.

What could cause that to happen?

Thanks again for the reply!
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Old Dec 5, 2023 | 09:28 AM
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2014 GL450, 1992 W140 300SD, 1993 W140 300SE, 1987 E30 Convertible
The rail was full of oil?
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Old Dec 5, 2023 | 09:34 AM
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2001 SL 500
OK so it's kinda hard to explain but the main rail where fuel would be at had no oil in.

Later today I have to take apart another gl450 fuel rail so I'll take pictures of what I find so it's easier to explain what's going on!
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Old Dec 5, 2023 | 09:42 AM
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2014 GL450, 1992 W140 300SD, 1993 W140 300SE, 1987 E30 Convertible
Your fuel run off line connected to crankcase through small hole in cylinder head cover. Crankcase is positive pressure system. Of course the line would be full of oil and its vapors
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Old Dec 5, 2023 | 09:53 AM
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2013 ML350 Bluetec
Originally Posted by arsupisemnet
Your fuel run off line connected to crankcase through small hole in cylinder head cover. Crankcase is positive pressure system. Of course the line would be full of oil and its vapors


If it is, check your crankcase ventilation system, There should be a slight vacuum when you take the 710 cover off.
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