Steve Dunne Posted August 4, 2019 Share Posted August 4, 2019 A few days ago I posted elsewhere that I was having problems with fuel tubing rotting in the half-gallon fuel bottles in my flight box. I have now had the fourth occasion in the past 2 or 3 years of the silicon tubing in my fuel bottles going cloudy and stiff, then wrinkling, then breaking off inside the bottle. The fuel is Propower 16%, decanted from gallon bottles into the 1/2 gallon bottles I keep in the flight box. I've used this fuel for donkey's years. The fuel tubing is standard 3mm bore from the LMS, and worryingly the same tubing that I use inside the fuel tanks... The tubing is all the coloured type, not used clear for some years. The damage appears to be in the tubing above the fuel level - i.e. in free air above the fuel. It hasn't happened (yet) to my Laser 5%. Any bright ideas? Steve. Most recent: Last time: .and... Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted August 4, 2019 Share Posted August 4, 2019 Only had this happen once years ago with some coloured silicone tubing that was new on the market . The green was the worst followed by the yellow . The current tubing in my flightbox tank is probably ten plus years old and fine. I only ever buy tubing that has a blueish tint now as it seem far more robust and less likely to split at the ends .I would guess that its nothing to do with the fuel but that the tubing is made of inferior material; however minor changes to the composition of fuel/ oil might be responsible as has the changes to petrol composition that now seem to rot nitrile tubing very quickly . Quote Link to comment Share on other sites More sharing options...
Don Fry Posted August 4, 2019 Share Posted August 4, 2019 I would guess that silicone tubing is made for all sorts of markets, with different formulations and specifications. And suppliers to our hobby are probably not to well acquainted with what they are buying when the rename it silicone fuel tubing. Like Engine Doctor says, I have some clear tube in my refuelling bottle. I have no idea how old it is, many years, and it's good. Quote Link to comment Share on other sites More sharing options...
J D 8 Posted August 4, 2019 Share Posted August 4, 2019 There is silicon tubing and there is silicon tubing. As with Don's mine has been in the fuel can on the flight box for many years and is fine. Quote Link to comment Share on other sites More sharing options...
Jon H Posted August 4, 2019 Share Posted August 4, 2019 I went through this several times with the tanks i use at work for engine testing. They are often left with fuel in them and are left out in the sun etc. I have also found glow fuel eats through brass quite efficiently under certain circumstances. Methanol is pretty savage stuff! Quote Link to comment Share on other sites More sharing options...
Steve Dunne Posted August 6, 2019 Author Share Posted August 6, 2019 Thanks for the comments. I think I will have to try to find some of the older, non-coloured tubing and try that. I just hope that the same problem does not happen inside the fuel tanks.... Steve. Quote Link to comment Share on other sites More sharing options...
Don Fry Posted August 6, 2019 Share Posted August 6, 2019 Steve, a fuel tank should be an annual pull out and inspect job. I don't bother on all of mine, but only ones where I don't care if the motor stops. Quote Link to comment Share on other sites More sharing options...
Steve Dunne Posted August 7, 2019 Author Share Posted August 7, 2019 I agree "should be" Don, but with nearly 20 large warbirds and other complex aircraft, it becomes a major operation. Many of them need the engine removing to get the tank out, so not a quick/simple task. On the odd ones that I have investigated or serviced in recent years, I have not seen any deterioration. The latest rotted silicone tubing was in the bottle only 4 months... I note that the rotting is only in the part of the tubing above the fuel surface - the submerged part was fine?!? Still confused but thanks for the comments. . Steve. Quote Link to comment Share on other sites More sharing options...
Phil Olson - Model Technics Posted August 7, 2019 Share Posted August 7, 2019 It could just be the sunshine doing the damage!!! Quote Link to comment Share on other sites More sharing options...
Steve Dunne Posted August 7, 2019 Author Share Posted August 7, 2019 That's a novel idea! I hope so - most of my tanks are well out of the sun!. I haven't heard of that before - is it a reasonable idea? Note that the same silicone tubing out of the top of the container (in the sunshine) appears not to be affected, it is just the bit inside the bottle above the fuel surface. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted August 7, 2019 Share Posted August 7, 2019 Combination of vapour and UV attacking the compound used to colour the tubing perhaps? Quote Link to comment Share on other sites More sharing options...
John Stainforth Posted August 7, 2019 Share Posted August 7, 2019 I leave some of my models for three month periods in cupboards with essentially no daylight. Yet I often have problems with tanks and rotted fuel tubing. I suspect the main culprit is the nitromethane in any residual fuel in the tanks and tubing. Nitromethane is a very aggressive chemical and the resistance of neoprene and silicon rubbers to it is poor. I looked this up on the web a short while ago and was interested to see that nitromethane is also cited as an excellent solvent of cyanoacrylate adhesives! (And it is also reckoned now to be more explosive than TNT!) I should add that I like fairly high nitro fuels (typically 12 to 15%) for most of my engines. Edited By John Stainforth on 07/08/2019 12:39:00 Quote Link to comment Share on other sites More sharing options...
Bruce Collinson Posted August 8, 2019 Share Posted August 8, 2019 Steve, Is it the pigment? On a practical level, the PS has lots of clear and pale blue and I have to pass within half a mile of it tomorrow. Last orders? Ty Trygon? BTC Quote Link to comment Share on other sites More sharing options...
Steve Dunne Posted August 8, 2019 Author Share Posted August 8, 2019 Hi Bruce, All my current silicone tubing came from the LMS... I'm not worried yet, as only the filler bottles are affected. I will probably buy some un-pigmented stock from elsewhere, when I am more sure about what is happening. I understand that Tygon stiffens over time when immersed in glow fuel with nitro added. Thanks anyway! Steve. Quote Link to comment Share on other sites More sharing options...
ROSS MANSELL 1 Posted August 8, 2019 Share Posted August 8, 2019 TYGON appears to be the scientific tube that is impervious to fuels/oils etc...expensive.. Its yellow in colour and has the name every 300mm down the tube to show its genuine. Quote Link to comment Share on other sites More sharing options...
Manish Chandrayan Posted August 8, 2019 Share Posted August 8, 2019 Posted by ROSS MANSELL 1 on 08/08/2019 10:13:31: TYGON appears to be the scientific tube that is impervious to fuels/oils etc...expensive.. Its yellow in colour and has the name every 300mm down the tube to show its genuine. I have had that stuff rot in pack. The pack had slimy precipitation at the bottom and all over the tube. Instead of investigating what it was I preferred to throw it all off. That stuff will also harden over time when in contact with petrol. Ultimately started using either Viton or PU type petrol tubing Quote Link to comment Share on other sites More sharing options...
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