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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54493
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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Hi, Ive got 1999 mercedes c250 turbodiesel & when its left

Customer Question

I've got 1999 mercedes c250 turbodiesel & when it's left for more than a few hours the fuel drains back into tank & it becomes very difficult to start.

It's been into my local garage & to a specialist diesel place & had loads of new o rings put into the filter housing. It's also been vacuum tested but everyone's baffled how air is leeching back into the the fuel line.

Submitted: 4 years ago.
Category: Mercedes
Expert:  Marty replied 4 years ago.

Hi, sorry for the wait. If air is entering the fuel system at the injection pump the shop has missed an air leak. You mentioned that the fuel filter housing has been resealed but these cars are notorious for air entering the system via the o-rings at any of the plastic fuel lines and also at the fuel shut off valve at the pump and around the delivery valves at the pump. The front pump seal can also leak but it is very rare. There is no other way that air can enter the system. The mechanic needs to work through the system from the inlet line to the fuel pump all the way through to the return line. I usually replace every plastic fuel line and replace the fuel shut off valve and inspect the fuel pump. He also needs to inspect the delivery valves at the top of the pump that feed each fuel injector for leakage.

Let me know if you have any questions.


Customer: replied 4 years ago.

Hi Marty,

Thanks for your reply.


I'm just going to print off your comments & show them to the mechanic.

So I'll let you know a little later if that's OK.


Thanks again,


Expert:  Marty replied 4 years ago.
You're quite welcome Nick. Let me know if you need anything.

Expert:  Marty replied 3 years ago.
Hi Nick, I never heard back from you about the car. Do you need anymore help with this? Let me know. If you would also take a moment to rate my service I would appreciate it.

Customer: replied 3 years ago.

Hi Marty,

The car's still at the garage; they've had it since Monday; it's being serviced as well as having this problem checked out.

Obviously, they've had to leave it overnight each time they try what you suggested.

They'll call me when/if they sort it or not. As soon as they do, I'll let you know.



Expert:  Marty replied 3 years ago.
Thanks for the update Nick.