Bubbles in fuel line?

[Heroez]

Hi, I installed one of those clear fuel filters before the mechanical pump on my 260z. When the engine is running, little bubbles of air can be seen forming in the glass filter, and there is always a large air pocket in there. The car runs and drives fine during normal driving. Are those air bubbles normal? If not, what does that indicate? I have not noticed any fuel leaks under the car or around the engine.

[seattlejester]

Not sure why the bubbles form, but it shouldn't pose a problem as the fuel all ends up in a bowl in the carburetors before it gets used by the engine.

 

My only guess would be either it just is the way it is the fuel is entering a relatively large volume compared to the line when it enters the filter, or you have a small crack in your fuel line or your fuel pickup and you are pulling in air with each cycle of the mech fuel pump.

[Tony D]

Yes, they are normal. It's also why it's important to orient the filter inlet and outlet. Get it wrong and those bubbles WILL cause a problem.

 

Take apart that front filter next time you change it, and you will see the outlet sucks from the bottom of that filter area, far away from where the bubbles are at the top. But if you turned it upside down, those bubbles could transfer into the fuel pump mechanism and they don't like air.... Especially electric pumps!

[Heroez]

Thanks for clearing that up. The clear glass filter is mounted semi horizontal just before the mechanical fuel pump. I see that a more propper position would be vertical like the stock fuel filter under the hood. I will study it when I replace the filter element. Learning is fun.