Drilling a hole in a plastic fuel tank: any problems I should know about first?

[chal]

Background: last winter I swapped old stainless fuel tank that had an outlet with a tap at the bottom of the tank for a new plastic tank with a syphon. I have had no end of trouble with this - try as I might, I cannot seem to stop air entering the system and collecting at the top of the syphon. I've been almost driven to drink on occasions (well, actually got there several times) and wished I'd left the old tank in place. Final straw: I went down to the boat a couple of days ago to find that the glass bowl on the bottom of the filter had broken (I suppose I must have over tightened it in my ongoing attempts to prevent air entering the system) and the entire contents of the tank, which was full, had dutifully syphoned itself into the bilge.

Now that the tank is empty, I am very tempted to drill a hole in the side an inch above the bottom and fit an outlet with tap. This might be less "safe" but the complete loss of all the fuel in the tank would actually be far less likely to happen.

The only issue I can think of is: would cutting a hole in the tank weaken it in such a way that it might be likely to split open, or is plastic not like that? It's a basic plastic tank - this one in fact http://shop4tanks.co.uk/plastic-tanks/osculati-fuel-tank-62-litres.html

NB that I am aware that I could fit a tap between the syphon and the filter which would have prevented this; in fact, when I first fitted the tank, I did include a tap in the line, but consensus was that it was one of the possible points of air ingress, so I took it out again.

Thanks!

 

[PetiteFleur]

I would find out where you have an air leak and your problems would be immediately solved without drilling holes. You have obviously tried hard to find the air leak, it sounds like you have a cav filter with the glass bowl at the base - I have just changed my old cav filter for an identical housing but for a screw on filter with drain tap. It will not leak and changing will be a doddle. I got it on ebay from ssldieselfilters from memory cost about £28 including a filter and I sold the old one on ebay.
On a previous boat I had the sam air leak and found 2 sealing rings in the housing!!

 

[chal]

Thanks for very quick reply. I take your point that finding the air leak would solve the problem but, as you say, I really have tried hard and there is a limit to the number of hours I can put into this. However, sounds like your filter might be good but I can't find it on ebay - searching on ssldieselfilters as seller returned nothing at all. However, they do have a website, and I can see quite a number of filters (though nothing costing around £28). Sorry to be a pain but would you mind having a quick look and letting me know if it is any of these: http://www.ssldieselparts.co.uk/filter-assembly-single-filter-assemblies-single-c-267_265_8.html

Thanks!

 

[VicS]

I am sure that the correct solution is as Petite Fleur suggests to find and cure the air leak in the existing connection,

Not clear From the Jay Wolfe website or from Osculati's website what the exiting outlet consists of.

I suggest PTFE tape for any tapered thread connection that must be air tight but don't over do it on plastic fittings or you will split them.

Take care not to overtighten joints that rely on O rings or you will distort the O ring and/or the fitting if its plastic.

The Universal outlet fitting kit

seems to use a couple of O rings but its not clear how this is assembled. There appear to be 3 possible leakage points: between the fitting and the dip tube, between the two halves of the fitting, between the fitting and the external pipework.

Drilling a hole for an outlet fitting in wall of the tank will not weaken it but you will still have to ensure the connections are leak proof or they will weep diesel continuously . Additionally you will have to ensure a leak proof joint between the fitting and the tank wall.

 

[HunterWanderer]

It could well be a faulty lift pump.
Debris in the fuel can stop the valves from seating and the pump will then not suck up the fuel.
The pump should have enough power to pull any air with the fuel through to the lift pump and then on to the main pump where air can be bled out. Usually though the pumps are good enough now to self prime, so no venting is needed.
Check the pump by starting with air in the fuel line, disconnect the fuel line at the main pump and turn the engine over on the starter motor. Fuel should be pulled up and delivered to the main pump after a few turns. If fuel doesent appear remove the lift pump and operate it with your thumb over the discharge it should be impossible to stop the air from being discharged.

 

[vyv_cox]

ASAP do a spin-on filter that is a replacement for the glass bowl type http://www.asap-supplies.com/search...filter-replacement-kit-for-cav-filters-302040 I have one that is a doddle to get leak free compared with the CAV ones, with which I have struggled most frustratingly. All the fittings are transferrable from the old unit. Only downside is that ASAP are currently out of stock but presumably they will appear again.

 

[chal]

ASAP do a spin-on filter that is a replacement for the glass bowl type http://www.asap-supplies.com/search...filter-replacement-kit-for-cav-filters-302040 I have one that is a doddle to get leak free compared with the CAV ones, with which I have struggled most frustratingly. All the fittings are transferrable from the old unit. Only downside is that ASAP are currently out of stock but presumably they will appear again.

That does look interesting and maybe one way of dealing with the leaks. Do you use an additional glass separator or just not bother with one at all?

 

[lw395]

On my first boat, I replaced the plastic take-off fittings on top of the tank with a brass 'bulkhead fitting' with a copper tube running right through it.
A 1/4 turn ball valve straight on top helped with filter changes.

My problem was diesel leaking out if the tank was over filled, the filler pipe held several litres and the tank only about 20 IIRC.

 

[alant]

L

Background: last winter I swapped old stainless fuel tank that had an outlet with a tap at the bottom of the tank for a new plastic tank with a syphon. I have had no end of trouble with this - try as I might, I cannot seem to stop air entering the system and collecting at the top of the syphon. I've been almost driven to drink on occasions (well, actually got there several times) and wished I'd left the old tank in place. Final straw: I went down to the boat a couple of days ago to find that the glass bowl on the bottom of the filter had broken (I suppose I must have over tightened it in my ongoing attempts to prevent air entering the system) and the entire contents of the tank, which was full, had dutifully syphoned itself into the bilge.

Don't use an electric drill, if there is any chance of a combustbe mixture still in tank.
If there is & it goes bang, might solve all your tank problems!
Now that the tank is empty, I am very tempted to drill a hole in the side an inch above the bottom and fit an outlet with tap. This might be less "safe" but the complete loss of all the fuel in the tank would actually be far less likely to happen.

The only issue I can think of is: would cutting a hole in the tank weaken it in such a way that it might be likely to split open, or is plastic not like that? It's a basic plastic tank - this one in fact http://shop4tanks.co.uk/plastic-tanks/osculati-fuel-tank-62-litres.html

NB that I am aware that I could fit a tap between the syphon and the filter which would have prevented this; in fact, when I first fitted the tank, I did include a tap in the line, but consensus was that it was one of the possible points of air ingress, so I took it out again.

Thanks!

 

[vyv_cox]

That does look interesting and maybe one way of dealing with the leaks. Do you use an additional glass separator or just not bother with one at all?

The downside is not having the glass bowl but only really a minor inconvenience. We brought the elderly, poorly maintained boat with this filter from Milford Haven to Port Dinorwic earlier this season. I was expecting fuel sludge problems and bought half a dozen filters beforehand. On the trip we lost the engine three times due to fuel filter blockage but it took less than a minute to replace it. When this happens with the CAV filter the pump sucks in air through the seal between the bowl and the filter, which can mean that the fuel system needs bleeding before the engine will restart.

 

[alant]

L

What happened to my post?

Anyway, don't use electric drill, if any chance tank has flammable mixture!

 

[David2452]

Don't even think about drilling holes in plastic fuel tanks, especially not below the fuel level, even putting fittings in the top, small ones anyway, (larger fittings with back flanges sandwiching the plastic are more successful) been there, done that and have a drawer full of the tee shirts. I had to resort to calling in a plastic welder to put on a boss on more than one occasion. I now use these http://www.aquafax.co.uk/html/product_specification.asp?ID=23439 and a reducing bush with repeated success.

 

[pvb]

Don't even think about drilling holes in plastic fuel tanks, especially not below the fuel level, even putting fittings in the top, small ones anyway, (larger fittings with back flanges sandwiching the plastic are more successful) been there, done that and have a drawer full of the tee shirts.

I'd second that! Remember that your plastic tank was rotationally moulded and the walls won't necessarily be a uniform thickness, so getting a fitting to seal properly below fuel level can be very difficult.

 

[lw395]

I'd second that! Remember that your plastic tank was rotationally moulded and the walls won't necessarily be a uniform thickness, so getting a fitting to seal properly below fuel level can be very difficult.

You need a good rubber gasket.
Neoprene is OK with diesel? (I'd check that...)
And a fitting with a suitable flange.

It's not acceptable for it to leak above the fuel level either.....

 

[VicS]

You need a good rubber gasket.
Neoprene is OK with diesel? (I'd check that...)
And a fitting with a suitable flange.

It's not acceptable for it to leak above the fuel level either.....

Nitrile, rather than neoprene, for diesel IIRC

 

[PetiteFleur]

Thanks for very quick reply. I take your point that finding the air leak would solve the problem but, as you say, I really have tried hard and there is a limit to the number of hours I can put into this. However, sounds like your filter might be good but I can't find it on ebay - searching on ssldieselfilters as seller returned nothing at all. However, they do have a website, and I can see quite a number of filters (though nothing costing around £28). Sorry to be a pain but would you mind having a quick look and letting me know if it is any of these: http://www.ssldieselparts.co.uk/filter-assembly-single-filter-assemblies-single-c-267_265_8.html

Thanks!

Search on ebay with "sfa11 filter assembly" and it will appear.
I've sent you a pm.

 

[David2452]

You need a good rubber gasket.
Neoprene is OK with diesel? (I'd check that...)
And a fitting with a suitable flange.

It's not acceptable for it to leak above the fuel level either.....

It's not so much the gasket, though that is inmportant, actually removing the flex from the tank is almost impossible with small fittings, unless you have access to the inside to fit a substantial flange along with one on the outside you are on to a loser. I tried on many occasions without success, contacting tank makers and fittings suppliers for assistance along the way, it was (is) imprortant to me as part of my living is drilling holes in tanks for fuel take off on a regular basis. Some of the welded thick wall tanks will work better, but moulded poly is a nightmare to seal as the sealed area flexes too much.

 

[CJU]

It's not so much the gasket, though that is inmportant, actually removing the flex from the tank is almost impossible with small fittings, unless you have access to the inside to fit a substantial flange along with one on the outside you are on to a loser. I tried on many occasions without success, contacting tank makers and fittings suppliers for assistance along the way, it was (is) imprortant to me as part of my living is drilling holes in tanks for fuel take off on a regular basis. Some of the welded thick wall tanks will work better, but moulded poly is a nightmare to seal as the sealed area flexes too much.

Out of interest, to supply a diesel heater from a plastic main fuel tank would you tee into the engine fuel feed, which is what I did on the recommendation of the suppliers, or drill into the top of the tank and use the kit supplied.

 

[David2452]

Out of interest, to supply a diesel heater from a plastic main fuel tank would you tee into the engine fuel feed, which is what I did on the recommendation of the suppliers, or drill into the top of the tank and use the kit supplied.

I now use the method I described earlier as a dip tube is always better than taking off the engine line or filter, but we did stop fitting standard dip tubes to poly tanks for a while due to the issues, during that short time I had bosses welded on to stiffen the area and fabricated a dip tube to screw into that, worked well, but was costly. Rock and a hard place really between teeing and a leaky dip tube, neither are acceptable in my book.

 

[pvb]

I now use the method I described earlier as a dip tube is always better than taking off the engine line or filter, but we did stop fitting standard dip tubes to poly tanks for a while due to the issues, during that short time I had bosses welded on to stiffen the area and fabricated a dip tube to screw into that, worked well, but was costly. Rock and a hard place really between teeing and a leaky dip tube, neither are acceptable in my book.

The "professionals" who installed a heater in my new boat drilled a hole in the plastic tank for the dip tube. The first time I filled the tank, there was diesel everywhere! I've resealed it as best I can, but I notice that the installation instructions for my Webasto specifically said not to install their dip tubes into plastic tanks.