Air bubble in fuel line - is it normal?

'In my SEAT Leon TDI, I can see an air bubble in the transparent fuel line (from the diesel filter to the pump). When the engine is running, air bubbles regularly appear in the line. Should I take it to the workshop (under warranty), or is this not a cause for concern?'

Hello,

Air bubbles during engine operation usually have simple causes, such as defective O-rings on the return valve, fuel lines that are not properly connected (or pinched) at the diesel filter, or a fuel filter that is too old (or clogged).
However, if you still have a warranty, it's likely the fuel filter, and it's probably the original one.

How many kilometers are on your car?

1. Fuel filter: yes or no?

If you have driven significantly more than 30,000 km, replace the filter and any O-rings on the return valve.
If the problem persists, I would recommend having it checked under warranty to find the leak. Issues like leaks in hard-to-reach places (e.g., a pipe inside the tank) can be difficult and time-consuming to locate.

Best regards, Rainer.

The car is only 4 months old and has 11,500 kilometers on the odometer.

How does it actually work? The pump surely pumps out more than is actually injected, right? Otherwise, I would surely notice the bubbles while driving, in the form of jolts, etc. Am I wrong in thinking that?

Yes, a variable displacement pump draws in more fuel than is actually consumed.

Best regards, Rainer.