UK Monster Owners Club Forum .: Technical :. Fuels & Oils » Ethanol test for pump petrol

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Old 02-10-2018, 12:35 PM   #46
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I've repaired a few steel tanks that have rotted though and they have all had the most serious corrosion on the side stand side at the lowest point which I took to be from the presence of water either though ingress or from aqueous ethanol coming out of solution.

Quite often what looks like just a small pinhole or two turns out to be the tip of the iceberg with whole areas around the holes left tissue paper thin.

I don't know the history of one particular tank that was holed and thin but had no visible rust on the area inside the tank. It may have had the rust removed/treated before it came to me but from the description above I guess it could have been acidic corrosion.
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Old 02-10-2018, 01:28 PM   #47
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Originally Posted by Luddite View Post
Scary stuff about steel tanks...
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Old 02-10-2018, 07:36 PM   #48
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Originally Posted by Luddite View Post
Having an 1100 Evo with a plastic tank, I've done quite a bit of reading into this subject. I don't want to sound like the voice of doom, DD, but it's not just us plastic tank owners who have to be careful; even steel tanks are not immune although they are at risk in a different way.

Obviously, they're not going to swell, but they can corrode. The corrosion mechanism works like this:

Fuel is left in the tank for some time.
The ethanol in the fuel absorbs water from the atmosphere.
Once the ethanol is saturated and cannot absorb anymore water, it comes out of solution with the fuel and, being heavier, sinks to the bottom of the tank ("phase separation").
Ethanol is a perfect food source for a particular microbe "acetobacter", which has been found in ethanol underground storage tanks.
Once the bacteria have feasted on the ethanol, they produce acetic acid, which is corrosive to mild steel.
The surface of the tank in contact with the ethanol will suffer from "aqueous corrosion" while any exposed area above the fuel will experience "gaseous corrosion". If you've ever opened your fuel cap after a winter hibernation and detected a faint whiff of vinegar, then that's acetic acid at work.

Perhaps potentially more damaging is the effect on any in-tank fuel pumps with their moving parts and critical clearances.

As I said earlier, I don't want to be a scare-longer - if you fill up every couple of weeks, then there won't be time for the ethanol to cause problems, (it's safe while it's in suspension with the petrol). But I think, if you're laying up your bike for any length of time, it's good practice to either drain the tank (and carbs if appropriate) or add an ethanol specific fuel stabilizer.

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