Found this early today,

Simple explanation about air bubbles in fuel flow:

https://www.parker.com/literature/Racor/Mobile_Air_Separation_In_Diesel_Fuel.pdf

Appears some bubbling is normal, just needs to be small enough to not cause noticeable engine hesitation.

A slight pressure drop helps bubbles develop. Fuel lines that are marginal or filters in the suction path can help cause bubbles. Those air bubbles do not disappear after the lift pump. Fuel vapor bubbles will disappear after the lift pump.

On the cars that have the small orifice built in the filter housing, it might be a good idea to check that orifice to make sure it is open to allow trapped air out. Might be a reason for engines hesitating now & then.

I'm not suggesting installing the Parker or any other brand of filter. Except for excessive water in fuel I think the Mercedes filter is adequate. Just wanted y'all to know about how air bubbles form in the fuel itself. Other air bubbles can come in when fittings are not good and air is sucked in to join the fuel flow.

You may have already seen this but its very informative
OM606 fuel supply issues

Again, the best approach to preventing cavitation would be to install an electric pump near the tank outlet. That would increase pressure throughout the system and pretty much eliminate the root cause. With the added benefit that you would have an easier time priming the system.

I'd imagine finding a leak by looking for fuel is easier than the trial and error method of finding an leak that sucked air in the lines.

__________________
84 300SD
85 380SE
83 528e
95 318ic

Ive heard adding the electrical pump actually doesn't work because. The system is supposed to only run at a specific low pressure.

On the 617 that is

__________________

Great info, thank you for sharing.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

On Fuel Injection Pumps with a Fuel Pressure Relief/Overflow Valve that once the Engine is running will pass small amount of Air out of the overflow circuit and back to the Fuel Tank.

In particular the Mercedes Diesels that don't come stock with a Hand Primer have an even better facility to pass Air.

Of course all the systems can be overwhelmed if the air leak is large enough.

__________________
84 300D, 82 Volvo 244Gl Diesel