My inj. return lines were cracking, so I got some translucent fuel line from the mower place, to see how tight the whole thing was. Well, I there are a lot of air bubbles in the return lines. The material is harder than normal, maybe not a good seal? The fuel filter has only a very small bubble in it. The vehicle runs well, are these bubbles a problem? There is quite a bit of air, even after running hard for a while.

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1981 300D 205,000 mi.

You mean the 1/8 inch injector return lines rather than the IP return line, correct?

I had clear lines on my injectors for a quick fix a couple weeks ago and they too had bubbles in them. However I didn't try and prime or purge the system after replacing so the bubbles could have been stuck. As long as the car is running well I wouldn't worry about it. You'd know when you have a lot of air going through your feed lines.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth