Air in the fuel line...

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zipster31

New Member
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Hello all, am sure this problem has been seen many times before ( have had a look elsewhere on this forum but can't find any info) so please bear with me. Have a BMW diesel P38, 1996. Can see air in the fuel line - in the clear pipe after the fuel filter. Have fitted a non-return valve just before the fuel filter, replaced the fuel filter housing, new pipe and connector from non-return valve to filter housing. Filter lightly smeared with oil before fitting (to stop rubber puckering). Have changed filter a couple of times and problem is persistent. When I leave the Rangie for a while - 1 day or half a day for example, there is a 4 inch long air bubble in the fuel line - hence is a pig to start and flattens the battery before starting. Am tired of using my 240v booster pack to start the old girl. Any ideas? Am lost and can't work it out.:doh:
zipster31
 
zipster31 said:
Hello all, am sure this problem has been seen many times before ( have had a look elsewhere on this forum but can't find any info) so please bear with me. Have a BMW diesel P38, 1996. Can see air in the fuel line - in the clear pipe after the fuel filter. Have fitted a non-return valve just before the fuel filter, replaced the fuel filter housing, new pipe and connector from non-return valve to filter housing. Filter lightly smeared with oil before fitting (to stop rubber puckering). Have changed filter a couple of times and problem is persistent. When I leave the Rangie for a while - 1 day or half a day for example, there is a 4 inch long air bubble in the fuel line - hence is a pig to start and flattens the battery before starting. Am tired of using my 240v booster pack to start the old girl. Any ideas? Am lost and can't work it out.:doh:
zipster31
Click to expand...

Have a look at the O rings either side of fuel filter. Also at the spill pipes on the injectors. Look at RAVE service bulletins for diesel bad starting.
 
May I ask which O rings either side of the filter? Do you mean the O rings on the end of the inlet/outlet pipe (if there are any o rings there). Spill pipes - I assume you mean the rubber return hoses from the injectors - they are fine. If they were ruptured, how would that create bubbles after the filter? Surely air must be coming in before the clear pipe as this is where the bubbles are coming from?
 
zipster31 said:
May I ask which O rings either side of the filter? Do you mean the O rings on the end of the inlet/outlet pipe (if there are any o rings there). Spill pipes - I assume you mean the rubber return hoses from the injectors - they are fine. If they were ruptured, how would that create bubbles after the filter? Surely air must be coming in before the clear pipe as this is where the bubbles are coming from?
Click to expand...

Spilloff is returned to the pump. When engine is hot fuel is hot and expands, when it cools it contracts and sucks air in if pipes are not good. Same with O rings they seal to prevent leaks by fuel pressure but air can be sucked back past them when fuel cools. Read RAVE as i said.
 
zipster31 said:
May I ask which O rings either side of the filter? Do you mean the O rings on the end of the inlet/outlet pipe (if there are any o rings there). Spill pipes - I assume you mean the rubber return hoses from the injectors - they are fine. If they were ruptured, how would that create bubbles after the filter? Surely air must be coming in before the clear pipe as this is where the bubbles are coming from?
Click to expand...

I replaced all my leak off pipes even though they looked fine when i took them off the pipes had small splits near the end. changed them and no longer had air in the system.
 
Replace the leak off pipes with silicone vacuum tube, I got the size from Wammers (thanks again Wammers) and purchased it on Ebay. Fiddly job but can be done without removing the manifold.
 
Datatek said:
Replace the leak off pipes with silicone vacuum tube, I got the size from Wammers (thanks again Wammers) and purchased it on Ebay. Fiddly job but can be done without removing the manifold.
Click to expand...

Ain't it strange, someone comes on and asks a question. Then when they are given the answer argue the toss. Strange old world we live in. If the questioner knows more than the one who gives the answer why ask in the first place? :cool::cool::cool:
 
wammers said:
Ain't it strange, someone comes on and asks a question. Then when they are given the answer argue the toss. Strange old world we live in. If the questioner knows more than the one who gives the answer why ask in the first place? :cool::cool::cool:
Click to expand...

Thank you everybody for your words of advice. I will replace spill off pipes as advised. I think you have misunderstood me Wammers. I have not argued the toss at all. I did not understand something and hence asked a question. Nothing wrong with that. Thank you once again folks for your help, yours words of advice have enlightened me!
zipster31
:)
 
zipster31 said:
Thank you everybody for your words of advice. I will replace spill off pipes as advised. I think you have misunderstood me Wammers. I have not argued the toss at all. I did not understand something and hence asked a question. Nothing wrong with that. Thank you once again folks for your help, yours words of advice have enlightened me!
zipster31
:)
Click to expand...

No problem mate hope it sorts it for you.Use 3mm bore silicone vacuum hose available on Ebay for a few quid. A lot better than the rubber stuff. And will last the life of the car.:):):)
 
Last edited:
Thank you for your advice folks. The 3mm silicone hose has done the trick. Am surprised it does not melt as is quite soft. The final solution was to fit the box of tricks that tricks the vehicle into thinking it is cold when hot - had a hot start problem also. All good on the starting front now. Now just have a battery drain problem - have started another post for that : )
 
wammers said:
No problem mate hope it sorts it for you.Use 3mm bore silicone vacuum hose available on Ebay for a few quid. A lot better than the rubber stuff. And will last the life of the car.:):):)
Click to expand...

Just had a quick look on eBAy it does state on the descriptions not suitable for fuel? Or does it mean not for a fuel line replacement?
Also the I'd is 3 mm?
 
Canyon said:
Just had a quick look on eBAy it does state on the descriptions not suitable for fuel? Or does it mean not for a fuel line replacement?
Also the I'd is 3 mm?
Click to expand...

I put a note on another thread about this last week. I changed my glowplugs last week and noticed that the silicone tube i had used for spill pipes was slightly swelled. They were still tight on the nipples with no sign of a leak. These pipes have been on for over a year. However i did change them for spill pipe available from PARTCO in a kit at £3.00 per metre. To replace all the spill piping you would need two kits. I know for a fact silicone is NOT suitable for unleaded petrol because of the additives in it. It would appear the fuel companies are adding things to diesel that can effect the silicone if only slightly. One of the biggest problems when vehicles which ran on leaded fuel were changed to unleaded, apart from the valve seat problem, was the fuel lines, which the unleaded fuel rotted quite quickly because of the chemicals added to it. It would appear diesel is following the same route. So anyone who has used the silicone just be aware and keep an eye on it.
 
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