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  #1  
Old 01-31-2018, 08:10 AM
E300d 1995
 
Join Date: Jun 2017
Location: Near Lake Texoma
Posts: 194
Found informative item on air bubbles in fuel

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.

Last edited by Texasgeezer; 01-31-2018 at 08:29 AM.
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Old 01-31-2018, 11:04 AM
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Join Date: Dec 2009
Location: Bedfordshire UK
Posts: 369
You may have already seen this but its very informative
OM606 fuel supply issues
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  #3  
Old 01-31-2018, 11:28 AM
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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.
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Old 01-31-2018, 05:58 PM
Shadetree
 
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There may be another advantage to that solution.

Quote:
Originally Posted by Mxfrank View Post
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.
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Old 01-31-2018, 07:50 PM
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Location: Seattle, WA
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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
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Old 02-01-2018, 10:20 AM
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Location: Oregon
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Great info, thank you for sharing.
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Old 02-01-2018, 01:52 PM
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Location: Long Beach,CA
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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.
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