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Air is or is NOT okay in fuel lines?

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Old 04-15-2007, 02:33 PM
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2009 c300
Air is or is NOT okay in fuel lines?

I have what I consider a large amount of air in my fuel lines. 2 seperate mechanics have told me "this is normal" - true? I have replaced all the clear lines and orings, also the fuel shut off was leaking - replaced entire unit. Car runs good, just wondering if air is sign of something bad???
Old 04-15-2007, 03:00 PM
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Year and model really helps.

What's a large amount of air to you? If it's a single large bubble in the clear filter, it's normal.
Old 04-15-2007, 03:09 PM
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Originally Posted by 240D 3.0T
Year and model really helps.
Sorry - 1999 e300td

The air is while running - the fuel in the clear lines ( all of them ) almost,but not quite, looks like foam. That's how many bubbles. It looks to be 30-40% bubbles. Seems like a lot to me. But like I said, car idles and runs great.
Old 04-15-2007, 06:15 PM
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Originally Posted by dylancarter
Sorry - 1999 e300td

The air is while running - the fuel in the clear lines ( all of them ) almost,but not quite, looks like foam. That's how many bubbles. It looks to be 30-40% bubbles. Seems like a lot to me. But like I said, car idles and runs great.
I had the same experience with my 1999 VW Jetta TDi. Lots of bubbles but no problem at all. I was worried insufficient fuel or too much air is going into the engine but the engine ran well.

The only problem was a noisy turbo when it starts spinning.
Old 04-16-2007, 10:42 PM
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Air in fuel will hurt fuel mileage, and increase black smoke.
Old 04-16-2007, 10:45 PM
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Air in fuel lines is bad. Should be causing the engine to knock louder and idle rough.
Old 04-16-2007, 10:45 PM
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2009 c300
Originally Posted by SmokinCummins
Air in fuel will hurt fuel mileage, and increase black smoke.
After reading everything I can I am thinking that the o-ring in the pre-filter may be bad. I am picking one up tomorrow - along with a new pre-filter and main filter.

I'll let ya'll know what happens
Old 04-16-2007, 10:49 PM
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2009 c300
Originally Posted by rsatmans
Air in fuel lines is bad. Should be causing the engine to knock louder and idle rough.
It's a little rough when I first start it, then mellows out.
Old 04-27-2007, 11:33 PM
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$10 fix

Well ya'll - $10 fixed everything. I changed the fuel filter and pre-filter, and still had all kinds of air in the lines. Grrrrrr. I had just had my fuel lines changed, what else could it be. I looked at my fuel line and 2 of them did not look like they had been changed. I changed the one from the heater(?) to the prefilter. When I took it off there was NO O-RING on one of the sides!!! Uhh, maybe that was it? Clicked my new $10 line on, and started her up. Runs like a champ and NO air in the lines.
Old 04-28-2007, 12:00 AM
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Originally Posted by dylancarter
I have what I consider a large amount of air in my fuel lines. 2 seperate mechanics have told me "this is normal" - true? I have replaced all the clear lines and orings, also the fuel shut off was leaking - replaced entire unit. Car runs good, just wondering if air is sign of something bad???
Air=bad

You should have zero air!
One bubble is too much!
Any body that tells you differently is wrong.

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