Drilling a hole in a plastic diesel fuel tank

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Oceanis

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I need to drill a 25mm hole in the top of my plastic diesel fuel tank which is about half full of fuel. I was thinking about using a hand drill and a 25mm bit and cleaning away any bits of plastic as I go. What would be the risks and can anyone suggest a better way of doing this. Removing and draining the tank really isn't an option.
 
I used an adjustable hole cutter with a point, not drill bit centre ( bought from http://www.ebay.co.uk/itm/1-New-Hol...Home_Garden_PowerTools_SM&hash=item20b2d0cbb6 ) to cut a 4" hole in my polyethylene diesel tank this year, removing swarf from the top until the hole cutter was about 90% through the plastic. Then followed round with a Stanley knife blade to cut the last bit, and I am sure no debris at all entered the tank, which was over 1/2 full at the time.

I had to do this to get inside to properly refasten fuel takeoff and return fittings that were held down by the builders by self-tappers, and were leaking at fitting/tank joint. Getting a good seal to polyethylene is hard, I had to have several goes at it, eventually cork/nitrile gaskets plus red hermetyte sealant seems to have worked. I have another leak now, but from a different fitting. Diesel really is difficult stuff to seal in to a flexible plastic tank....
 
Keep a hover right next to where you are drilling. Hover it up as you go. A few bits might fall in but there are plenty old steel tanks with a lot worse that a few bits of plastic in them. You filters will trap any bits that might find their way into the fuel lines.
 
Proper hole saw with a load of grease on it to collect the swarf, low speed, clean up ragged edges with a craft knife, I do similar sized holes for heater standpipes using that method and never had an issue, though I know some have issues when done on different areas of the tank. I will not do it unless on a thick tank, right at the top and on a flat area though.
 
jwilson said:
I used an adjustable hole cutter with a point, not drill bit centre ( bought from http://www.ebay.co.uk/itm/1-New-Hol...Home_Garden_PowerTools_SM&hash=item20b2d0cbb6 ) to cut a 4" hole in my polyethylene diesel tank this year, removing swarf from the top until the hole cutter was about 90% through the plastic. Then followed round with a Stanley knife blade to cut the last bit, and I am sure no debris at all entered the tank, which was over 1/2 full at the time.

I had to do this to get inside to properly refasten fuel takeoff and return fittings that were held down by the builders by self-tappers, and were leaking at fitting/tank joint. Getting a good seal to polyethylene is hard, I had to have several goes at it, eventually cork/nitrile gaskets plus red hermetyte sealant seems to have worked. I have another leak now, but from a different fitting. Diesel really is difficult stuff to seal in to a flexible plastic tank....
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Great idea but the adjustable hole saws only go down to 30mm. I could use a 25mm hole saw and replace the arbor bit with a shorter point rather than a drill bit.
 
David2452 said:
Proper hole saw with a load of grease on it to collect the swarf, low speed, clean up ragged edges with a craft knife, I do similar sized holes for heater standpipes using that method and never had an issue, though I know some have issues when done on different areas of the tank. I will not do it unless on a thick tank, right at the top and on a flat area though.
Click to expand...

Do you think I could get away with using a battery powered drill? I'm just not sure about how flammable diesel is!!
 
Don't worry about a battery drill, diesel has a high flash point (>60C) and is quite difficult to ignite without a wick. Just clear out fuel soaked rags and you should be fine. To be honest it isn't that easy even with a wick but better safe than sorry.
 
I tried a ole saw with lots of grease, it didn't work for me, I got swarf and a disc of plastic in the tank. Maybe I wasn't careful enough. Luckily the tank was easy to remove and drain and clean.
 
If you have access into the tank float a plastic dish on the diesel under where you are drilling the hole to catch all the swarf.

Battery drill will not be a problem with diesel. I have used a mains drill to drill holes in my steel diesel tanks several times.
 
LittleShip said:
You could try heating a piece of pipe and using it to melt the hole you need,removing any scarf carefully with a Stanley knife.

Tom
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I would definitely do it this way - no swarf just carefully remove the small ridge created on the edge of the hole with a knife

Pete
 
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