So when I first bought this car a year ago, the first odd thing I noticed was that it had no inline fuel filter, only the screw on. Regrettably I did not install one until about two months ago. I should mention that I've been having some extremely rough cold starts for the past 3 months, too which i reacted by using some diesel addative with cetane booster, changing the glow plugs, adding the inline fuel filter, an oil change, and a new battery. However if the temp gets close to or below freezing, its still a ***** to start.

So now that I have the inline pre-filter installed, I'm able to see air bubbles rushing in. I know a pocket of air in the filter is expected even after bleeding with the hand pump(I have the new version btw), but I'm seeing a constant rush of bubbles while the engine runs.

So if I understand correctly, fuel is coming from my tank to the inline filter, through that to the fuel pump, and then straight to the injectors, or is it going through the screw on filter before reaching the injectors. It looks to me like the screw on filter is only filtering overflow diesel heading back to the tank via return lines. Am I wrong about that?

Either way, I just want to know if anyone thinks this constant flow of visible air could cause these rough starts in cold weather, and lately, hard idling. And has anyone ever dealt with this. I have searched the forums and it seems most "air in the fuel filter" stories don't talk about seeing an actual flow of bubbles.