Fuel Tank Repair

[drh1965]

Could a "plastic" diesel tank from 1987 be anything other than polyethylne? I need to make a small repair and would like to weld it.

Thanks

[GordMay]

“Plastic” Fuel Tanks are generally made from High Density Crosslinked Polyethylene Resin (HDXLPE), which has a melting point of around 130 degrees C (about 266 degrees F).

[drh1965]

Does anyone have any experience with using a hot glue gun to make a repair? I read in an RV forum that this works well on Poly holding tanks. I just want to seal some small drill holes.

[GordMay]

Nope, hot glue won't stick.
Heat to about 275 deg. F, then use a poly' weld stick, or just smear the heated tank wall around.

[Kanani]

Gord's right again........The only way to seal up Polyethylene is to weld it with a proper plastic welder and Polyethylene welding rod.

if you can access the inside of the tank, why not just put a S/S nut, bolt and a coulpe plastic washers?

If you can't access the inside of te tank you could get some of those nuts that expand as you tighten them.

[drh1965]

Thanks guys. I can't use a bolt because the holes were drilled by the PO to attempt to seal a leak around the sender unit and the bolts/nuts would interfere with the sender. I fixed the original problem with an under-ring but when I press down on the tank, I can't hear a minute amount of air coming out under the sender gasket. I'm probably being anal but I don't want a problem when the boat is heeled.

The thought of heating the tank up enough to melt the poly makes me nervous. Seems like I could easily make the problem worse. Is it hard to do a plastic weld?

[Kanani]

Originally Posted by drh1965

Thanks guys. I can't use a bolt because the holes were drilled by the PO to attempt to seal a leak around the sender unit and the bolts/nuts would interfere with the sender. I fixed the original problem with an under-ring but when I press down on the tank, I can't hear a minute amount of air coming out under the sender gasket. I'm probably being anal but I don't want a problem when the boat is heeled.

The thought of heating the tank up enough to melt the poly makes me nervous. Seems like I could easily make the problem worse. Is it hard to do a plastic weld?

It isn't hard to complete the weld. You just need a welder like this one:
Harbor Freight Tools - Quality Tools at the Lowest Prices

It would be best to get another piece of Polyethylene to weld over the top of the holes. Filling the holes can be a little more tricky.

You don't have to worry about igniting the diesel fuel. There is no flame and it doesn't get hot enough to ignite diesel fuel.

[mike d.]

why don't you try bedding the sender gasket in 4200 before welding. clean the tank surface with acetone let dry then apply gasket etc. and let sit until cured! the tank is vented isn't it? if so you should not build pressure to cause a problem.

[drh1965]

OK, I completed the repair. It was quite easy. Melted some plastic milk jobs sections into the holes with tape on the under side. Worked fine.