1997 W202 C250 TD - cold start bubbles in fuel lines

G-C250

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Hi everyone, since i got my 97 C250 TD it was fine at starting through the warmer summer months. However, since winter im having to pump the primer in the engine and turn the ignition repeatedly until the battery is almost flat. Eventually it fires up but its taking a massive toll on the starter. I can visibly see many air bubbles in tbe fuel lines when im pumping the primer. So im sure air bubbles are getting in somewhere but i cant see where. Once it fires up it will fire up all day long and drives great. Im leaving it in to the garage on Wednesday to have tbe O-rings replaced. Im wondering of there are any more things i should have done whilst its in the garage. I dont want to lose heart in the old motor... any suggestions would be much appreciated...
 

LostKiwi

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Supply side o rings are the common cause of this.
 
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G-C250

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Supply side o rings are the common cause of this.

Supply side O-rings??? Can u elaborate a bit pls.. im not too in tune with the lingo (being a nurse lol)
 
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G-C250

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Thanks LostKiwi
 

om613

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Someone's added a primer, which they don't have, so another potential ingress site there.
 

robparker

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Someone's added a primer, which they don't have, so another potential ingress site there.

Just what I was going say, instead if solving the original problems of fuel lines and o-rings (as suggested above) they made it worse by adding a primer, remove it, replace the fuel lines, she'll be good to go!
 

yorkshire1

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get the glowplugs checked, more than a couple gone and it wont like starting regardless of air bubbles!
 
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G-C250

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Glow plugs have been changed already. Its going in on wed to the merc clinic to have o rings replaced and checked over for any other leaks.. The guy at merc clinic is very good and reasonably priced... fingers crossed i will update the post afterwards... thanks folks
 
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G-C250

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Just what I was going say, instead if solving the original problems of fuel lines and o-rings (as suggested above) they made it worse by adding a primer, remove it, replace the fuel lines, she'll be good to go!

When i say primer, i mean the little balloon-like pump on the fuel line (apologise, my lingo stops outside medical terms ). Do these not come as part of the old c250's??
 

robparker

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No, someone has fitted that instead of resolving the original problem, get rid of it as it's just somewhere else for air to get sucked in
 

om613

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Make sure they also change the 'shut off valve' O ring (in this weird diesel fuel system).
They seldom get done, and yes they go flat like all the others.
 

dbanbery

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Get the whole set of pipes replaced, they last longer as the originals go brittle and literally ANY air ingress into the system bypasses the fluid lock in the system and runs back into the tank. It shouldn’t have a primer bulb, and the reason you have to crank it forever is because there is no lift pump in the fuel tank like modern cars.

The pipes from Merc will cost less than £100 and they come with o-rings.


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G-C250

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Get the whole set of pipes replaced, they last longer as the originals go brittle and literally ANY air ingress into the system bypasses the fluid lock in the system and runs back into the tank. It shouldn’t have a primer bulb, and the reason you have to crank it forever is because there is no lift pump in the fuel tank like modern cars.

The pipes from Merc will cost less than £100 and they come with o-rings.
Cheers DBanbury... that will be ny next step should the problem not be solved after tomorrow. Left it in to garage today... will let you all know how i get on. Much appreciated everyone.

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dbanbery

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I’d strongly recommend the whole pipes doing, it’s less fiddly, simpler (no potential to ruin the new orings). And I’ve done it to four cars


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Doug1234

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What fuel level is the tank at when you get the hard starting ?, if its low it may be the cause of the air bubbles. Do a search for saddle tank syndrome / problems.
 

dbanbery

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What fuel level is the tank at when you get the hard starting ?, if its low it may be the cause of the air bubbles. Do a search for saddle tank syndrome / problems.

If the filter in the tank is full of clagg it normally starts fine, and then when you get it up to speed for a bit it empties the filter of fuel and conks out.

What’s this saddle take syndrome?


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Doug1234

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Tank is basically like two halves that should balance fuel level out between themselves via pipes and return flow from engine, but this all goes wrong and one side empties and engine stops.
Most engines stop around 1/4 tank level, its a common problem and internet is full of various cures from adding a low flow facet pump to balance fuel level out to the simplest one which is keeping tank full and never letting it go below 1/2 full.
Do a search on this forum and have a read up.
 
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G-C250

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Its usually around 1/4 to 1/2 full... i dont drive it often enough to notice a difference as its only driven at weekends. But i will keep that in mind should the replacement o-rings not do the trick today.
 

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