Fuel Leak? Air Bubbles? Get Help Now!

Hi everyone,
"I've been struggling with air bubbles in the fuel supply line for quite some time. My AFN engine has lost power, and I believe it's related to the air bubbles. I've tried everything to get rid of the bubbles, but so far without much success. The entire fuel supply line has been replaced (fuel sender, fuel line, filter, etc.). I even installed a Monopoel filter head without a return valve, but that didn't work either. The air bubbles only appear after the car has been running at idle for a while. It seems like a vacuum is forming. However, even opening the fuel cap or completely removing the fuel sender didn't make a difference. I'm at my wit's end! The air bubbles probably originate from the line coming from the fuel tank."

Maybe it's the hose clamps! I have no idea! Are there any specific clamps that you can recommend, or any sealant that can be applied to the connections? Does anyone have any ideas???

Greetings.
Reuselkopp.

Did you use rounded hose clamps?
They can look like this, for example:


In contrast:

Hi,
Yes, exactly, I used the rounded ones.

What do the return lines from the injectors look like?

Hi,
"No, these oil cooler hoses aren't new. I replaced them with other used ones once during a nozzle change. But, why would it be caused by leaking oil cooler hoses?"

reuselkopp wrote:

Hi, Yes, the oil cooler hoses are not new. I had replaced them once during a nozzle change with other used ones. But, why should it be due to leaking oil cooler hoses?

hi reuselkopp,
And that could be the topic.
"In my case, there was a collection of hoses installed between the ESD devices."
I bought the original ones, and everything was fine.

best regards, leo

For V6 TDI engines, the reuse of used oil feed lines is strictly prohibited.
Otherwise, you could try running the engine from a bottle or a canister.

Hi,
Okay, I'll start by replacing the vacuum hoses and then I'll let you know if the car is still drawing in air.

Hi everyone,

"I completely replaced the oil cooler hose yesterday, but the air bubbles are still there. Do you have any other ideas? Is there something like a sealant that I can apply between the hose and the plastic connection?"

Greetings.
Reuselkopp.

Hi,
Are you absolutely sure that air is being drawn in?
Or is there simply air trapped in the line and unable to escape?

Best regards,

@Kalle,

How do you mean that? Where is the air supposed to come from? The return line is active, and fuel should actually be vented through it.

reuselkopp wrote:

The entire fuel system was replaced (fuel level sensor, fuel line, filter, etc.). I even installed a filter head without a return valve from Monopoel, but that didn't work either.

The air bubbles only appear after the car has been running at idle for a while.
Hi,

if you're already putting in so much effort, it shouldn't matter anymore if you temporarily replace the entire section of piping between the fuel level sensor and the filter with a long piece of clear tubing.
With that, you can see if the bubbles are already coming from the tank .

@Ulf,

I just checked, and the bubbles aren't coming from the tank. I suspect the problem might be in the connection in the engine compartment.

reuselkopp wrote:

The bubbles are not coming from the tank. I suspect now that it must be the connection in the engine compartment.

Okay... did you still have no air bubbles between the filter and the ESP when using the long, clear hose?

Have you checked the sealing ring on the diesel filter yet? I once had a filter where this sealing ring was defective! It let in a lot of air!

Hi,
The air is already present in the line before it reaches the filter.