Leaking fuel filter

D

Daydream believer

Well-Known Member
Joined
6 Oct 2012
Messages
23,576
Location
Southminster, essex
Visit site
Every year i have had problems with sealing the joint between the top of the glass bowl & the filter or the filter & the top part of my water trap filter ( CAV)
i have changed the whole filter in case there was a distortion.
I have tightened it to the point of actually shattering the glass bowl
I have fitted butterfly nuts to the mounting bolts so i can remove the whole assembly & put together easily ( it is a little innaccessible in the engine bay)
Yet to my utter frustration i always seem to get a slight leak.
I know it is there because i have positioned some kitchen roll in various places & it stains if there is any drips on to it
The rubber sealing rings never seem to work & i have changed them frequently

Can anyone give some tips on how to get a good seal on the filter
 
Have you tried thoroughly cleaning out the groove that the seals fit in on the mount? Any muck there would break the seal. An old motorcycling trick for a leaking fuel tap was to smear the working surfaces with vaseline. Sounds unlikely, but it worked, permamnently. A smear of vaseline on the O ring seal might just do the trick.

Do not allow the glass to rotate when you are tightening down, it can distort the seal and cause it to leak.


Any other ideas anyone/
 
Last edited:
Had a similar problem with my CAV's. Tried & tried over & over again to get a seal. In the end I found the cause was a very slight difference in the size of the new filter. It looked & seemed fine but what was happening was as I tightened the screw the
seal was being twisted & hence the leak. Have you tried a different make of filter ?
 
oldharry said:
Have you tried thoroughly cleaning out the groove that the seals fit in on the mount? Any muck there would break the seal. An old motorcycling trick for a leaking fuel tap was to smear the working surfaces with vaseline. Sounds unlikely, but it worked, permamnently. A smear of vaseline on the O ring seal might just do the trick.

Do not allow the glass to rotate when you are tightening down, it can distort the seal and cause it to leak.


Any other ideas anyone/
Click to expand...

The same trick works for leaky forehatch seals.
 
I have changed from glass bowl to metal water separator, admittedly you cannot see what is happening but it does seem to seal better. There is then one less seal to leak as well. I can recommend the Racor spin on but the filters are expensive. I have added one so have the CAV filter followed by the racor.

Also worth checking the fuel line connections as when I changed mine found they where loose.

Good luck with it.
 
I am beginning to think about an earlier comment where it was suggested filters vary in size
I will take a gauge to the boat & try the filters
I currently have- new Holland- Davidson- & volvo filters all purchased from different sources

I suspect that is the clue. But i will get some Vaseline. If only to smear on my cracked knuckles
 
Strange you are having problems, the one fitted on Ronhilda seals every year without problems. It should seal well before you have tightened so much the glass shatters.

As others have said groove must be clean
Seal ring is slightly different (bigger) size to the ring used for the element to the metal top cap, my filter was fitted in 1987 so a later version may differ.
Prewetting the rubber ring with diesel helps rather than fitting dry. Have also used grease on these rings when end caps are well corroded such as found on ships lifeboats engines.
Check your central spindle is straight, if you have tightened so much the glass bowl has broken it may well be off centre
Do not tighten too much or risk of rubber seal(s) becomig deformed.


Brian
 
According to WoodyP on PBO forum, anyone who cannot seal a CAV filter is a 'cack-handed spanner monkey'. http://www.ybw.com/forums/showthread.php?350892-Diesel-filter-vacuum-gauge-and-CAV

I am included in those numbers, as I have persistent problems with them. I have descended to applying a smear of 'instant gasket' to the seal, which seems to work. It seems to me that it's the tapered joint that is at the root of the problem. The accuracy of fit required seems to be beyond the capabilites of the manufacturing equipment.
 
Sandyman said:
Had a similar problem with my CAV's. Tried & tried over & over again to get a seal. In the end I found the cause was a very slight difference in the size of the new filter. It looked & seemed fine but what was happening was as I tightened the screw the
seal was being twisted & hence the leak. Have you tried a different make of filter ?
Click to expand...
Changed from a CNH filter to a New Holland one today
Problem solved
I could not see the size difference with my aged eyes
However, a gauge showed the New Holland one to be 0.9 mm bigger on the outer bottom rim & 0.8 mm across the rebate
Many thanks for your solution
It was only a thimble full leaking after a few days but i cannot tolerate the smell of diesel in the boat
I now have 3 spare filters that do not fit
 
Viv, I'm sorry if my tongue in cheek bon mot still rankles. The problem for you is that you aren't a bodger but please don't take it personally. I find a spannner makes a better hammer than a screw driver.

vyv_cox said:
According to WoodyP on PBO forum, anyone who cannot seal a CAV filter is a 'cack-handed spanner monkey'. http://www.ybw.com/forums/showthread.php?350892-Diesel-filter-vacuum-gauge-and-CAV

I am included in those numbers, as I have persistent problems with them. I have descended to applying a smear of 'instant gasket' to the seal, which seems to work. It seems to me that it's the tapered joint that is at the root of the problem. The accuracy of fit required seems to be beyond the capabilites of the manufacturing equipment.
Click to expand...
 
Chris _Robb has the right answer.
CAV are a problem waiting to happen if you have to search for the right brand, not just the 296 number.

I just changed to spin-on filters with a drain tap to check for water & muck.
 
Chris_Robb said:
This appears to be a very common problem with the CAV. The best way to cure it is to get rid of it and put in a system that is clean, quick and easy to change the filter, especially in an emergency at sea.

This is what I put in
http://www.parker.com/portal/site/P...00FG+FUEL+FILTER/WATER+SEPARATOR&Wtky=FILTERS
It requires a little more space, but I was glad I had done it.
Click to expand...
The problem- as i see it- is that for the centrifuge to work there must be a flow fast enough to generate the spin- am i right?
I note they are talking about 200 litres per hour & i use 2 litres per hour
So i suspect it would not work on a small engine in a yacht- or would it
 
Daydream believer said:
Every year i have had problems with sealing the joint between the top of the glass bowl & the filter or the filter & the top part of my water trap filter ( CAV)
i have changed the whole filter in case there was a distortion.
I have tightened it to the point of actually shattering the glass bowl
I have fitted butterfly nuts to the mounting bolts so i can remove the whole assembly & put together easily ( it is a little innaccessible in the engine bay)
Yet to my utter frustration i always seem to get a slight leak.
I know it is there because i have positioned some kitchen roll in various places & it stains if there is any drips on to it
The rubber sealing rings never seem to work & i have changed them frequently

Can anyone give some tips on how to get a good seal on the filter
Click to expand...

Yes. After 20 odd years of the same sort of issue, I discovered last year that the two big filter rings you get arent the same. They are slightly different sizes and one of them will only seal with difficulty if put in the wrong place. Study them carefully and you will see what I mean.
 
Daydream believer said:
The problem- as i see it- is that for the centrifuge to work there must be a flow fast enough to generate the spin- am i right? ....
Click to expand...

Yes, that is what still happens but at low velocities. The fuel is directed both downwards and outwards as it enters the bowl. The large denser material transfers to the outside of the bowl where it falls down due to gravity which is where this differs from a high speed fuel centrifuge. In a high speed fuel/oil cleaner an internal bowl like device with large surface area spins at high speed which provides the velocity to clean fuel, not the velocity of the fuel entering the device. Both devices use low centripetal forces to allow the solids to move away from the main flow path of the fuel. A high centripetal force is caused by high shear forces between the particles of fuel which would keep the denser matter in the fuel flow path. As the shear rates are low in diesel, the centripetal forces are low and thus the denser matter shears its way across the fuel flow path to the outside and drops out. In the high speed version the clean fuel and contaminates both move in the same direction but at different distances from the centre of flow. So, both use the same principle.
 
Bosun Higgs said:
They are slightly different sizes and one of them will only seal with difficulty if put in the wrong place. Study them carefully and you will see what I mean.
Click to expand...

Spot on. I suspect this is the main reason some can't get a proper seal, apart from trying to fit it dry.
 
Years ago I worked for CAV Rotax. Without a doubt you have answered your own question inadvertantly. Assuming you have the right seal ring in place the most common reason for these leaking is over tightening which distorts the housing. Once this distortion has been caused it will never seal properly and needs to be replaced. USE LESS WELLY!!!
 
Bosun Higgs said:
Yes. After 20 odd years of the same sort of issue, I discovered last year that the two big filter rings you get arent the same. They are slightly different sizes and one of them will only seal with difficulty if put in the wrong place. Study them carefully and you will see what I mean.
Click to expand...

Yes i had that one sussed from the start- but thanks anyway
I have been playing with diesel engines since when i was a teenager one of my jobs was to service the 30 odd mixers & dumpers on the firm
I regularly had them stripped own & de coked
But that was 45 years ago & being older some of my hard won skills now fail me
However, i do not ever recall that a slight difference in filter diameter causing me such hassle
As an aside-
I always remember when i became MD, one of our old contract managers making a mistake of some sort( forget what it was now)
I gave him a right rollicking & telling him that it was him that taught me how to do that some years earlier so how the hell could he justify getting it wrong now
However, now i am as old as he was, i am finding that i too am getting things that i once took for granted wrong
I think it is old age catching me up!!
Still damned annoying that i could not put a filter together without a leak & without coming to this forum though!
 
You must log in or register to reply here.

Share this page

Top