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The thin steel float used in my car (which was built in the UK in the early 60s, which I'm assuming is why it's not originally plastic) has rusted to a point where it's leaking in fuel and therefore failing to operate as desired.

I'm planning to replace it with a plastic float, but obviously want to make sure I'm not using something that could dissolve in the petroleum. I notice that 5 litre plastic canisters are HDPE so I intend to use that, but I'm intrigued as to just how much it matters. Plenty of discussion around the net suggests that most plastic bottles are likely to dissolve, most of which in my experience are PET. But this chart suggests PET is as good as HDPE:

http://www.plasticsintl.com/plastics_chemical_resistence_chart.html

That chart doesn't have data on PP or PE interestingly (though I assume HDPE has the same properties as PE).

So my question, respecting that storing petroleum in plastic containers not explicitly rated for the task is a bad idea, which plastics will actually dissolve? If it's a grey area is there a minimum thickness?

tjbp
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  • It seems like the chart that you linked to answers the question in your title. You end up with a question about how long various plastics will last. That is a much harder question. If you are really looking for an answer to the last part, you may want to [edit] your text to make it more focused on that part. – hazzey Jun 16 '17 at 13:54
  • What is it use for - carburettor float or fuel sender unit? – Solar Mike Jun 16 '17 at 15:34
  • @hazzey - true, I should have been more clear that the chart appears to conflict with the consensus basically everywhere else - am hoping for someone with the chemical knowledge to set the record straight. – tjbp Jun 16 '17 at 16:32
  • @SolarMike it's a fuel sender unit – tjbp Jun 16 '17 at 16:33
  • How about going to a scrap yard and finding a similar one in plastic - there are many cars that use similar systems... – Solar Mike Jun 16 '17 at 16:48
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    Those that know plastics know there is no consensus. It's a crazy world out there, but HDPE made from one grade of resin will have different crosslinking then the other grade, and that can be enough to change chemical compatibility. Heat exposure or reduction can convert LDPE to HDPE, which react differently to chemicals! Always check your material against your chemical before purchasing. – Mark Jun 21 '17 at 19:20

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There is a wide world of plastics, and a wider world of corrosive fluids to pit them against. Then within each plastic are different resins, brands, each with unique manufacturing methods. Some plastic resins have actually been formulated to be more corrosion resistant against one type of chemical and less against another while still being chemically identical. Most companies just lock the vast data of corrosion testing in giant matrices that become to vast for casual comparison, and you immediately jump to your favorite chemical and just run the row of plastics. http://www.hipco.com/ChemGuide.cfm is usually a good source for this, then. There are others, and official books, but the bottom line is - investigate thoroughly before making plastics decisions.

Mark
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The carburetor float on my'69 MGB sank. It happened abruptly while I was driving. I diagnosed it before taking anything apart when I saw a stream of gas on the road following me, while the engine died at the same time. When I pulled the translucent plastic float I saw that it was more than half full of fuel. I tried squeezing it in various ways to empty it without any luck until I poked it with a needle. After that it stayed afloat for several months. When it sank again I bought a new, identical float which lasted as long as the car. I hated buying parts from the dealer because the clerk always bid farewell by saying, "See you tomorrow."

In your case, I wouldn't spend time searching for a better designed replacement. You should carefully open up your corroded float, then fill it with something like styrofoam before gluing it back together.

toiler
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  • One car parts supplier in the UK had a slogan along the lines of "Yes, now what's your question" which rapidly became (as parts were usually not in stock) : "Yes, we haven't got one" !! – Solar Mike Jun 21 '17 at 14:31