Fixing hairline crack in plastic expansion tank?

[Hereward]

I have a small coolant leak on the top surface of my expansion tank at the male breather hose connection. It only leaks when the tank heats up and pressurises.

I would prefer to fix it rather than buy a new tank.

I was thinking of using a soldering iron to melt the plastic in the area. The melting then re-setting should seal the hairline crack, but knowing my luck I will probably start a fire.

Alternatively can anyone recommend a chemical fix, something that can leach in to and then seal a tiny crack? Any advice gratefully received, the solution needs to be pressure and heat resistant.

Thank you.

[GreenV8S]

The fact it's failed here suggests this area is under strain and makes me think that no repair is likely to have much of a chance, because it's unlikely that any repair would be as strong as the original. If you have nothing to lose then I suspect that plastic welding is going to be your best bet (i.e. using some compatible 'filler', not just trying to heat up the crack and melt the two sides into each other) but I suspect you're wasting your time.

[PositronicRay]

You could try and support the joint on the outside with fibreglass, but only regard it as a temporary repair.

[steveo3002]

replace it before it leaves you stranded , not the sort of part to save money on

[227bhp]

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

[Little Pete]

I've tried to repair these in the past with limited success. Replacement is the best way.

[E-bmw]

For what will be a cheap part from a scrappy I wouldn't waste my time trying to fix it......It will go again & these things always happen at the worst possible time/place according to sods law.

[ou sont les biscuits]

227bhp said:

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

To be pedantic, fibreglass doesn't stick to anything. It's the (normally) epoxy resin you coat it with that does the sticking. There may be some sort of resin that would stick to plastic, but as others have said it's liable to be a bodge at best, and not having the cooling system pressurise is probably not a good thing.

[227bhp]

ou sont les biscuits said:

227bhp said:

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

To be pedantic, fibreglass doesn't stick to anything. It's the (normally) epoxy resin you coat it with that does the sticking. There may be some sort of resin that would stick to plastic, but as others have said it's liable to be a bodge at best, and not having the cooling system pressurise is probably not a good thing.

To be just as pedantic fibreglass is usually used with Polyester resin and that doesn't adhere to plastic.

[ou sont les biscuits]

227bhp said:

ou sont les biscuits said:

227bhp said:

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

To be pedantic, fibreglass doesn't stick to anything. It's the (normally) epoxy resin you coat it with that does the sticking. There may be some sort of resin that would stick to plastic, but as others have said it's liable to be a bodge at best, and not having the cooling system pressurise is probably not a good thing.

To be just as pedantic fibreglass is usually used with Polyester resin and that doesn't adhere to plastic.

Depends what you're using the fibre glass for. Me, I mess around in plastic boats, and the resin normally used for repairs is an epoxy

[dave_s13]

The plastic shelf in my fridge door cracked and the replacement cost was ridiculous. I couldn't get any glue that would work.

I used a bit of the same kind of plastic from an unused drawer in the garage beer fridge and used that to effective weld it back up. Not pretty but it's worked a treat.

If you can get hold of something made of the same kind of plastic then you may be able to bodge that over the crack using a soldering iron.

[PositronicRay]

ou sont les biscuits said:

227bhp said:

ou sont les biscuits said:

227bhp said:

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

To be pedantic, fibreglass doesn't stick to anything. It's the (normally) epoxy resin you coat it with that does the sticking. There may be some sort of resin that would stick to plastic, but as others have said it's liable to be a bodge at best, and not having the cooling system pressurise is probably not a good thing.

To be just as pedantic fibreglass is usually used with Polyester resin and that doesn't adhere to plastic.

Depends what you're using the fibre glass for. Me, I mess around in plastic boats, and the resin normally used for repairs is an epoxy

Doesn't it depend on the plastic? It's GRP after all.

[ou sont les biscuits]

PositronicRay said:

Doesn't it depend on the plastic? It's GRP after all.

I think what 227 is getting at is that whatever resin you use, they don't stick terribly well to the sort of 'oily to the touch' plastics that they make expansion tanks out of. An epoxy resin might stick a bit better than polyester initially, but whether it would last I have no idea. I suspect not, but you'd have to try it to find out. And, if it failed, you're back to running your cooling system unpressurised.

[phillpot]

dave_s13 said:

If you can get hold of something made of the same kind of plastic ............

A new tank ....




Depending on the price of new (good second hand?) tank you might want to try Permatex but I don't think it's cheap stuff ?

[Hereward]

phillpot said:

Depending on the price of new (good second hand?) tank you might want to try Permatex but I don't think it's cheap stuff ?

That's just what I was hoping for. Many thanks, I just bought a pack on Amazon.

I enjoy fixing things and if this doesn't work then I will replace the tank.

Thanks for the comments. I should add the crack is absolutely tiny and the coolant loss is measured with teaspoons. Most owners wouldn't even notice.

[227bhp]

PositronicRay said:

ou sont les biscuits said:

227bhp said:

ou sont les biscuits said:

227bhp said:

Fibreglass doesn't stick to plastic.
Replacement is the best way, but if you want to try and patch it up then i'd go with the soldering iron bodge, poke it into the crack and smear it down with a screwdriver.

To be pedantic, fibreglass doesn't stick to anything. It's the (normally) epoxy resin you coat it with that does the sticking. There may be some sort of resin that would stick to plastic, but as others have said it's liable to be a bodge at best, and not having the cooling system pressurise is probably not a good thing.

To be just as pedantic fibreglass is usually used with Polyester resin and that doesn't adhere to plastic.

Depends what you're using the fibre glass for. Me, I mess around in plastic boats, and the resin normally used for repairs is an epoxy

Doesn't it depend on the plastic? It's GRP after all.

That raises the question; Define plastic.

We used to use plastic containers when mixing up, when it had set you just gave them a bit of a massage and the old dry resin just dropped out.
Other types of plastic (Polystyrene) will just melt on contact with it.

[Chees on wheels]

If it is HDPE try welding it with a soldering iron using the plastic strips cut from a supermarket milk carton! Worked for my water butt!