1998 300TD - Diesel starvation - AIR ??

[Ben Cocks]

I am having a very frustrating time with a 300TD having just spent hundreds of pounds on the fuel system to supposedly rid it of air. If I leave the car for more than 12 hours it won't start due to air in the fuel line - quite visible in a clear pipe if I open the bonnet.This has been replaced together with the fule filter and glow plugs.

I don't want to get ripped off at another garage and am thinking of taking it to the Merc Specialists in Skipton.

Can anyone shed any light on A- the problem and B my proposed choice of garage ?

Many thanks

Ben

 

[Blobcat]

Fuel run back tubes from the injectores perforated letting air in?

 

[Ben Cocks]

Thanks Blobcat - I'll give it a whirl !

Ben

 

[Bolide]

Air in fuel system

As yours is an early W210 it's very similar to a late W124. Air in the fuel system is a known problem and there are a number of things you can do but I suggest you return it to the people who did the work and ask them to finish the job. They may be more helpful than you think

I've found the normal cause is that the O rings in the fuel system flatten with age and then leak when disturbed. Typically this will happen after a service. The cure is to remove all the plastic pipework and replace the O rings - they're about 80p each from a dealership. Some people recommend greasing them to make a better seal but I'm not convinced

Second thing is to fit a non-return valve in the fuel feed close to the fuel filter. It's a factory-sanctioned mod for W124s

Once you've done all this, if the problem continues you'll have to look for perished or damaged pipework, damaged parts or a leaking stop valve

Nick Froome
www.w124.co.uk

 

[pcman_jh]

Air ingress

My C250 Diesel's air ingress was caused by the fuel bleed off rubber piping that runs between the injectors. Althought they looked OK visually, they crumbled in my fingers when I went to replace them (which is straight forward job).

I had already changed all O rings on my fuel system, the fuel heater, the seal on the cut-off valve to find it was the (cheap costing) rubber pipes that had showed their age.

 

[Bolide]

Fuel return pipes

My C250 Diesel's air ingress was caused by the fuel bleed off rubber piping that runs between the injectors. Althought they looked OK visually, they crumbled in my fingers when I went to replace them (which is straight forward job).

I had already changed all O rings on my fuel system, the fuel heater, the seal on the cut-off valve to find it was the (cheap costing) rubber pipes that had showed their age.

That's useful to know. Annoying though it may be to replace bits that may not be at fault I think it's a good idea to go through the whole fuel system to cure this problem. You're probably now clear for another 5-10 years

Nick Froome
www.w124.co.uk

 

[230K]

As yours is an early W210 it's very similar to a late W124. Air in the fuel system is a known problem and there are a number of things you can do but I suggest you return it to the people who did the work and ask them to finish the job. They may be more helpful than you think

I've found the normal cause is that the O rings in the fuel system flatten with age and then leak when disturbed. Typically this will happen after a service. The cure is to remove all the plastic pipework and replace the O rings - they're about 80p each from a dealership. Some people recommend greasing them to make a better seal but I'm not convinced

Second thing is to fit a non-return valve in the fuel feed close to the fuel filter. It's a factory-sanctioned mod for W124s

Once you've done all this, if the problem continues you'll have to look for perished or damaged pipework, damaged parts or a leaking stop valve

Nick Froome
www.w124.co.uk

The factory kit of non-return valves is available from dealers £10.88 + vat and part no. B6 6 54 8198.

230K

 

[Bolide]

Non-return valve

The factory kit of non-return valves is available from dealers £10.88 + vat and part no. B6 6 54 8198.

230K

Thank you - that's really useful. There are seven in stock at MBUK as of today. Or six now I've ordered mine

Nick Froome
www.w124.co.uk

 

[230K]

Bolide

In the kit you get an inline non return valve mechanical and an electric stop valve, local guy i know says to throw away the mechanical one and fit two of the electric valves one on the feed and one on the return.

I bought my kit and was going to fit it but renewing the o ring on the stop solenoid together with the 5 plastic lines cured my problem although i still have a small amount of trapped air just as the line enters the pre filter.

Cheers,

230K

 

[Bolide]

Stop valve

Thanks for the info. FYI the stop valve can leak. If it does a replacement is only about £10

You've got the basis of a great immobiliser with the electric valve. Just wire the valve feed via a hidden switch and you have a simple fuel feed shutoff

If your car has the ATA Anti Theft Accessory you can also quite easily route the starter motor feed via another (or the same) switch. If it doesn't have ATA you'll have a bit more cable to run but a starter cutout is always useful

Nick Froome
www.w124.co.uk

 

[Jonners]

Ben,

I have an identical problem with my E300TD Avantgarde Estate - (98 'R').

There is air visibly in the fuel pipes and non-starting that has got progressively worse.

Can you confirm how you resolved your problem? Was it through fitting a non return valve kit from MB?

Would you advise this is tried before changing the many fuel feed and return pipes around the pump and fuel filter??

I would be very grateful for a quick call or email to try and avoid some of the expensive frustration..!

Regards and thanks,

John - 01494 569392 or 07970 056881

 

[230K]

Jonners

I would replace the o ring on top of the prefilter probably best to renew the whole plastic pipe it is around a £5. Also check for any sign of wetness around the shut off solenoid on the side of the injection pump. Some advise replacing all the plastic pipes and o ring on solenoid. As a last resort fit the non-return valves.

230K

 

[Parrot of Doom]

Would you advise this is tried before changing the many fuel feed and return pipes around the pump and fuel filter??

If they're old and yellow, and leaking, replace all of them. They're not expensive. If you replace only 1 or 2, the leak will simply move to the others I know from experience

You can get easy access to them by removing the windscreen washer bottle. The two lines on the underside of the fuel shutoff valve (you should also order an O-ring for that) can be tricky to remove, they get stiff with age.

 

[42864]

Air Leaks

One old trick that we used to use on trucks to find a air leak on the fuel system was to disconect the fuel line at the tank and pressurise the system with an air line, and watch for the tell tale spray of mist/ deisel from the leak. I knowthat the fuel tank is harder to get at on a car than a truck but it is aethod worth thinking about.

Dave

 

[Hibbo]

I'm not doubting anything that's been said by people who know much more about these engines than I do, but could anyone explain how perished injector spill-off lines allow air to enter the fuel supply lines? Surely if they were letting air in it could only find it's way to the return line?