Glass fibre fuel tanks - degradation.

rogcal · Post by **rogcal** » Mon Jul 18, 2011 5:25 pm

The fuel tank in my VP1 has started to leak from the top of all places but the worrying aspect of this is that it leaking at all.

Constructed of glass fibre at the same time as the aircraft was built some 30 odd years ago (the top of the tank forms the top of the fuselage aft of the firewall), I would have hoped that its life would have well exceed three decades but apparently this is not the case.

There are several locations on the top where fuel is seeping through and all affected areas seem to be where the gel coat has failed and the fibres have become brittle and easily break away when even gentle probed.

Is this degradation of the glass fibre usual in fuel tanks of this age or could it be the affects of ethanol?

I some how doubt if the latter has been the cause, as the aircraft has been laid up for two years and I doubt if the ethanol was present in the fuel prior to that.

Having Googled the issue of glass fibre tanks degrading after long term exposure to petrol, there is a distinct possibility that the problem with my tank stems from bio deterioration where microbes present in the fuel attack the glass fibre leading to the degradation I have described. Scary or what!

Shortly after I purchased the aircraft in late 2008, I noticed the paint on the top of the tank beginning to bubble up in the same locations where I've now discovered the leaks.

At the time I put it down to the possibility of the new paint applied by the previous owner just prior to the sale, reacting to the old paint over which it had been applied and didn't even consider that the tank was unsound, particularly as the schedule of works for the aircraft for the permit issued prior to sale included an item relating to the repair of the tank.

So, what to do now?

I was considering opening up the tank and laying up new glass fibre over the degraded areas but I take the view that the entire tank is likely to be affected and carrying out repairs will be a waste of time and with ethanol being an ever present threat to the fuel system in general, I shall probably opt to fabricate an aluminium tank and remove the risk of the tank becoming compromised again in the future.

I wonder how many glass fibre tanks in homebuilts constructed over 20 years ago are on their last legs!

tnowak · Post by **tnowak** » Mon Jul 18, 2011 9:36 pm

Exactly the same thing happened on a friend's aircraft earlier this year. Fuel suddenly started to seep through the front of the fibreglass tank. Fibreglass repair didn't work so he had a new aluminium tank made.
Tony Nowak

rogcal · Post by **rogcal** » Wed Jul 27, 2011 3:58 pm

I can't positively identify ethanol in fuel as the cause but I've now found that one of the rubber boots that connect the inlet manifolds on my VW engine has failed.

If I hadn't been checking the spark plugs for indications of lean/rich mixture, I might have missed it but as all the plugs on two cylinders had very light grey deposits on them, whereas the plugs on the other cylinders were noticeable darker, I investigated the cause and found the rubber boot had softened and split.

Luckily, the VW after market product manufacturers have come up with a silicone rubber replacement part which I have ordered and when fitted will remove another risk area in the fuel system that would have been affected by ethanol.

I'd recommend that those of you running VWs with rubber boots on the inlet manifolds consider swapping them for the silicone variant or at least check your existing ones for signs of deterioration.

The worst that could happen could be a hole in a piston crown through a weak mixture followed by a forced landing which is exactly what happened to VP1 G-BGLF a couple of decades ago and although not attributable to the rubber boot (it was in fact a loose nut on the cylinder head to inlet manifold joint), the result was the same.

rogcal · Post by **rogcal** » Fri Jul 29, 2011 4:55 pm

Further to my post regarding the rubber inlet manifold sleeves/boots being degraded by ethanol in fuel and that the silicone variant would not suffer the same fate.

Today I received my "silicone" boots which I'd ordered online from a long established VW parts supplier and was shocked to find they were manufactured from urethane and not silicone as advertised.

As urethane is affected by ethanol, I immediately rung the supplier who didn't even realise the product supplied to them had changed and was no longer silicone.

Needless to say I got a refund and the supplier has now changed the description.

Following this I contacted two other suppliers of "silicone" boots and in both cases they found the products on their shelves were also made from urethane and they have now also changed their description.

I did eventually find a supplier of the silicone boot and have ordered a couple of pairs as it appears that they have limited stocks and don't know if they will be able to get any more.

It beggars belief that the US manufacturer of these silicone boots has switched to urethane from silicone, when it's well known that any of the urethanes are not compatible with ethanol and in some US states 20% of ethanol in fuel is becoming standard!