ipw
Well-Known Member
Have got a problem with air leaking into diesel fuel lines when engine running have tightened all unions and joints. Is their a product that seals joints like a grease that dosn,t harden,maybe spray on.
sucking air ?
- Thread starter ipw
- Start date
kirielad
Well-Known Member
Maybe a split in the rubber diaphragm on the diesel lift pump ?
Talulah
Well-Known Member
I have found the diesel/water seperator as the source of an air leak before.
Avocet
Well-Known Member
Had a mate with a similar problem on an old Perkins. It turned out to be an almost invisible hole in a steel tube that had been chafing against its bracket that held it to the engine.
Csail
N/A
I had the same...took ages to find.Worst bit was it would run for about 5 hours before stopping and the moment it stopped on one occasion was in a f7 against a very strong tide...lifeboat.
whipper_snapper
Well-Known Member
Don't forget the possibility that the pick-up pipe in the tank may be leaking. You can get corrosion at the top and they have been known to fall off entirely. A good indication is if the problem gets worse as the tank level drops.
fluffc
Well-Known Member
[ QUOTE ]
have tightened all unions and joints.
[/ QUOTE ]
Could you have over tightened them - this will cause an imperfect seal and air to leak in?
have tightened all unions and joints.
[/ QUOTE ]
Could you have over tightened them - this will cause an imperfect seal and air to leak in?
pvb
Well-Known Member
First step...
Your quickest first step would be to undo and remake all joints using a suitable sealing compound on the olives. Once you're sure the joints aren't leaking, if you still have an air leak you can investigate further.
Your quickest first step would be to undo and remake all joints using a suitable sealing compound on the olives. Once you're sure the joints aren't leaking, if you still have an air leak you can investigate further.
oldharry
Well-Known Member
Re: First step...
[ QUOTE ]
Your quickest first step would be to undo and remake all joints using a suitable sealing compound on the olives.
[/ QUOTE ] ... which In my experience is the quickest way to create more problems! (Been there and regretted it - every time!) To check the fuel system for leaks, carefully clean off every trace of muck and diesel specially round any joints, olives, seals etc. Dont forget things like bleed screws. Now go to Tescos and buy a roll of pink loo paper (well any colour will do, but pink seems to show up any moistening of the tissue best).
Run the engine up for 5 or ten minutes. Now carefully go over every joint with the loo paper - any leak will show up instantly as darkening of the paper. And if fuel is getting out, air is getting in. Every time the injector pump takes a 'gulp' of fuel it depresurises the entire fuel sytem momentarily, so that any leak ' goes in to reverse' and draws air in.
If the fuel system definitely has no leaks, and is still drawing air, then the leak is in the fuel lift pump, usually the diaphragm has a pin hole (therefore invisible) leak.
Why does sealant not work on olives? Because olives are designed to seal by soft metal contact, and because such a thin film is involved if a sealant is introduced, it can not do its job properly, and sooner or later (usually sooner!) it is either forced out by the pressure pulses of the various pumps, or if you are unlucky, sucked in to wreck the injectors! Its the same problem as trying to seal a 'dry fit' head gasket with additional sealant - the sealant actually holds the joint apart, then gets blown out by the fluctuating pressure.
In any case if the olives and seals already damaged by overtightening then no amount of 'sealer' is ever going to make them fuel tight again.
[ QUOTE ]
Your quickest first step would be to undo and remake all joints using a suitable sealing compound on the olives.
[/ QUOTE ] ... which In my experience is the quickest way to create more problems! (Been there and regretted it - every time!) To check the fuel system for leaks, carefully clean off every trace of muck and diesel specially round any joints, olives, seals etc. Dont forget things like bleed screws. Now go to Tescos and buy a roll of pink loo paper (well any colour will do, but pink seems to show up any moistening of the tissue best).
Run the engine up for 5 or ten minutes. Now carefully go over every joint with the loo paper - any leak will show up instantly as darkening of the paper. And if fuel is getting out, air is getting in. Every time the injector pump takes a 'gulp' of fuel it depresurises the entire fuel sytem momentarily, so that any leak ' goes in to reverse' and draws air in.
If the fuel system definitely has no leaks, and is still drawing air, then the leak is in the fuel lift pump, usually the diaphragm has a pin hole (therefore invisible) leak.
Why does sealant not work on olives? Because olives are designed to seal by soft metal contact, and because such a thin film is involved if a sealant is introduced, it can not do its job properly, and sooner or later (usually sooner!) it is either forced out by the pressure pulses of the various pumps, or if you are unlucky, sucked in to wreck the injectors! Its the same problem as trying to seal a 'dry fit' head gasket with additional sealant - the sealant actually holds the joint apart, then gets blown out by the fluctuating pressure.
In any case if the olives and seals already damaged by overtightening then no amount of 'sealer' is ever going to make them fuel tight again.
pvb
Well-Known Member
Re: First step...
[ QUOTE ]
Run the engine up for 5 or ten minutes. Now carefully go over every joint with the loo paper - any leak will show up instantly as darkening of the paper. And if fuel is getting out, air is getting in.
[/ QUOTE ]I'm not sure you've fully understood the original question. As far as I can see, the problem was that air is leaking in - fuel isn't leaking out.
[ QUOTE ]
Every time the injector pump takes a 'gulp' of fuel it depresurises the entire fuel sytem momentarily, so that any leak ' goes in to reverse' and draws air in.
[/ QUOTE ]Now that's an intriguing concept! /forums/images/graemlins/confused.gif
[ QUOTE ]
Run the engine up for 5 or ten minutes. Now carefully go over every joint with the loo paper - any leak will show up instantly as darkening of the paper. And if fuel is getting out, air is getting in.
[/ QUOTE ]I'm not sure you've fully understood the original question. As far as I can see, the problem was that air is leaking in - fuel isn't leaking out.
[ QUOTE ]
Every time the injector pump takes a 'gulp' of fuel it depresurises the entire fuel sytem momentarily, so that any leak ' goes in to reverse' and draws air in.
[/ QUOTE ]Now that's an intriguing concept! /forums/images/graemlins/confused.gif
rjp
Well-Known Member
Re: First step...
Bear in mind that it's possible for air to get in even if fuel is not getting out. I had that problem with a flexible fuel pipe from my filter to the fuel pump but it was a devil to find.
John
Bear in mind that it's possible for air to get in even if fuel is not getting out. I had that problem with a flexible fuel pipe from my filter to the fuel pump but it was a devil to find.
John
pvb
Well-Known Member
Re: First step...
[ QUOTE ]
Bear in mind that it's possible for air to get in even if fuel is not getting out.
[/ QUOTE ]That's exactly the point I made. I've had the same problem on my current boat, which has the main fuel tank deep in the keel under the engine and therefore generates a fair bit of suction in the pipes, especially if the fuel level is low. I ended up remaking all the compression joints, using a smear of jointing compound, and solved the problem. Jointing compound is an acknowledged sealant for pipework joints in lots of industries. On the feed to a diesel engine, it can't be "forced out by the pressure pulses of the various pumps" as oldharry said, because the feed pipe is basically under light suction all the time the engine's running. Similarly, it won't be "sucked in to wreck the injectors" because there's a fuel filter on almost every engine.
[ QUOTE ]
Bear in mind that it's possible for air to get in even if fuel is not getting out.
[/ QUOTE ]That's exactly the point I made. I've had the same problem on my current boat, which has the main fuel tank deep in the keel under the engine and therefore generates a fair bit of suction in the pipes, especially if the fuel level is low. I ended up remaking all the compression joints, using a smear of jointing compound, and solved the problem. Jointing compound is an acknowledged sealant for pipework joints in lots of industries. On the feed to a diesel engine, it can't be "forced out by the pressure pulses of the various pumps" as oldharry said, because the feed pipe is basically under light suction all the time the engine's running. Similarly, it won't be "sucked in to wreck the injectors" because there's a fuel filter on almost every engine.
vyv_cox
Well-Known Member
Re: First step...
"Jointing compound is an acknowledged sealant for pipework joints in lots of industries."
Maybe, but fuel systems is not one of them. Many problems can result from its use, particularly deposition of unwanted burnt material on nozzles, resulting in poor spray characteristics and consequent rough running, excessive fuel use and possibly worse. Your point about leakage where the tank is sited below the engine is valid but possibly not a very common situation? For the majority of installations an air leak will be a fuel leak when the engine is not running.
The answer is to check very carefully and renew olives where leakage is occurring. Better still, renew them all anyway.
"Jointing compound is an acknowledged sealant for pipework joints in lots of industries."
Maybe, but fuel systems is not one of them. Many problems can result from its use, particularly deposition of unwanted burnt material on nozzles, resulting in poor spray characteristics and consequent rough running, excessive fuel use and possibly worse. Your point about leakage where the tank is sited below the engine is valid but possibly not a very common situation? For the majority of installations an air leak will be a fuel leak when the engine is not running.
The answer is to check very carefully and renew olives where leakage is occurring. Better still, renew them all anyway.
aluijten
Well-Known Member
I've had this problem as well. I solved it by replacing all the sealing rings in the joints by new ones. Most of them only allow a few times being re-used.
If you bleed your engine by loosening fuel lines the sealing rings tend to wear out.
Spend a few quid on new sealing rings (originals from the engine manufacturer) and save a lot of time.
Do not go for any liquid sealant, you will regret it in the end as others have stated already.
Cheers,
Arno
If you bleed your engine by loosening fuel lines the sealing rings tend to wear out.
Spend a few quid on new sealing rings (originals from the engine manufacturer) and save a lot of time.
Do not go for any liquid sealant, you will regret it in the end as others have stated already.
Cheers,
Arno
T_Apprentice
New Member
Many diesel engines have low pressure injector spill pipes located in between the injectors and usually passing back to the fuel tank by a return pipe. I have seen installtions where the spill connection is returned to the lift or fuel pumps and therefore, this innocent rubber hose or pipe can be the source of air ingress where the hose or pipe is split or any unions are loose. Let us know what the solution is anyway. <span style="color:black"> </span>
macnorton
Well-Known Member
Easy! spray the fuel lines /filters with shaving foam, it will disolve where the leak is.
Then wash it off?
Then wash it off?
Aja
Well-Known Member
Is this a troll?
If you are experts in engine renovations you should know the answers, surely?
Your WEBSITE!!!!
Donald
If you are experts in engine renovations you should know the answers, surely?
Your WEBSITE!!!!
Donald
Billjratt
Well-Known Member
I painted the lines, joints and even part of the Racor with hammerite. Fixed. (volvo md11d with tank above)
Cliveshep
Well-Known Member
Re: sucking air ? re MacNorton
Gillette or will Tesco's own do?
Gillette or will Tesco's own do?
Talbot
Well-Known Member
lockseal - made by the same company as loctite.
I spent a miserable summer a couple of years ago trying to trace a leak in my system, and eventually replaced the lot, only to discover the leak was in the fitting on top of the tank that some muppet had made with teflon tape!
I spent a miserable summer a couple of years ago trying to trace a leak in my system, and eventually replaced the lot, only to discover the leak was in the fitting on top of the tank that some muppet had made with teflon tape!
