Results of BoatU.S. Sponsored Fuel and Fiberglass Gas Tank Tests
Soon after the Long Island Sound area of New York switched to gas mixed with ethanol, BoatU.S. began receiving calls from boaters who owned older gas-powered boats with fiberglass fuel tanks. The tanks, it seemed, were being slowly dissolved by ethanol; black stuff was building up on valves and intakes, destroying engines and some fuel tanks were becoming soft and even weeping fuel. Since then, BoatU.S. has sponsored several tests to find out exactly what the problem is. Here are the results of what we have learned so far. We’ve highlighted the important aspects in each case.
Tests of the black material from an intake valve:
“A portion of the black material was scraped from the intake valve, pressed flat, and transferred to a potassium bromide crystal plate. The sample was then analyzed by Fourier Transform Infrared Spectroscopy (FTIR), which produced an infrared spectrum. As indicated on the spectrum, the peaks at 2800-3000 cm-1 are due to Carbon-Hydrogen absorptions; the strong absorption at 1730 cm-1 can be from Esters or Ketones. The small sharp peaks at 1460 and 1370 cm-1 are indicative of Hydrocarbons. Finally, the large broad peak seen from 1000-1200 cm-1 is due at least in part from Carbon-Oxygen single bond absorbers. It can be said that this spectrum is consistent with the presence of polyester, whoever this cannot be unequivocally proven from this spectrum alone.”
Test of fuel from an affected boat:
EPA 8260 fuel analysis of a sample of fuel taken from a 1968 Bertram 31 located on Long Island Sound indicated 736,426 µg/L of styrene, a component of polyester resin.
Test of sections of fiberglass fuel tanks from a 1967 and 1970 Bertram:
Testing Summary:
To date, the testing done by IMS, LLC indicates that the two fuel tank samples have undergone some aggressive degradation (40% of their strength). The bottoms of both tanks have lost more strength than the tops. The older tank (1967) was laminated to a much higher level of quality in terms of entrapped air and fiber roll out. The mode of property reduction in the newer tank (1970) appears to be both resin softening and loss of adhesion between fiber and resin. This is evidenced by a moderate loss in both strength and stiffness. The older tank has lost nearly a similar amount of strength but has retained all its original stiffness. This indicates some resin degradation has occurred but no loss of the fiber/resin interface’s integrity has occurred.
Both tanks were produced using a fire retardant resin system although we feel the base resins for each tank are of a different type. Both tanks have absorbed in the range of 4.2% fuel into their volume over time (tank bottoms). The top of the newer tank has also absorbed over 4% fuel. The top of the older tank has absorbed 2.2% fuel over time.
Tests of Fiberglass Fuel Tank Samples
We recently analyzed intake valves having heavy, black deposits under the crowns. The valves we have received to date had been taken from gasoline engines in older yachts that had recently changed over to gasoline containing ethanol. Bent pushrods and bent valves have been reported with heavy engine damage when pistons impacted the valves.
We removed some of the black sludge from under an intake valve crown. We soaked the sludge in ethanol and, after taking the extract down to dryness, we obtained the infrared absorption spectrum. We found that the material is di-iso octyl phthalate.
We ran a series of experiments using straight gasoline and gasoline with 10% ethanol on fiberglass coupons and coupons of filler taken from one of the fuel tanks of the vessel from which the valves had been taken. Shortly before engine failure that vessel had changed over to gasoline having 10% ethanol. The results can be summarized as follows:
With both the straight gasoline and the gasoline having 10% ethanol, analysis by Gas Chromatography Mass Spectrometry (GCMS) shows that the fuel's lightest fractions were absorbed into both fiberglass and filler. Noting the very high flammability and volatility of these light organic compounds, boaters needs to be alert to possible outgassing and fire/explosion hazards.
GCMS shows that the gasoline having 10% ethanol picked up four very heavy molecules from the fiberglass and two from the filler. The molecular weights of these molecules were in the range of 281 to 379. The straight gasoline did not pick up these molecules. Evaporating the straight gasoline we were left with a thin film. Evaporating the samples that had picked up the heavy molecules we were left with heavy, brown sludge. Infrared spectroscopy showed molecular similarities between the sludge, and the material taken from under the intake valve crowns.
This is what we believe is happening:
Polyester resins, gel coats and fillers commonly incorporate phthalates. In even the best resins and layups a small proportions of these phthalates remain unreacted. There are several water soluble molecules that are found in these materials and they play a central role in blister formation and delamination. Phthalates are only sparingly soluble in water, however many are readily dissolved by ethanol.
Whereas gasoline free from ethanol never picks up phthalates, when ethanol was introduced the very small ethanol molecules diffused into the fiberglass, filler and gel coat materials where they dissolved unreacted phthalates. Having been dissolved by smaller molecules, and almost certainly accelerated by osmotic pressure, some portion diffused back to the surface and was dispersed in the gasoline. Based on our GCMS results to date there are some other, presently unidentified, large molecules that were also leached out by the ethanol and similarly transferred into the gasoline.
This internal solution and diffusion back to the surface is the process of leaching.
Since they are in solution, the phthalates and the other heavy dissolved molecules are able to pass through the fuel line filters. When the gasoline with ethanol evaporates in the carburetor the heavy molecules do not evaporate but come out of solution and are carried along in the air-fuel mix as an aerosol. When the droplets impinge on throttle plates and on the walls of the induction system they can collect as reported by Chuck Fort at BoatU.S. We do not presently know if after impingement the films are immobile or if they are able to migrate through the induction system towards the intake valves. Some of the molecules that impinge on the hot valve stems and under the crowns decompose to leave carbon powder and ash. Others, such as the phthalates that in general have exceptional high temperature stability, remain intact or undergo only partial decomposition and then act as the binder that holds together the carbon particles and ash as the observed, black sludge.
Frederick G. Hochgraf,
Senior Scientist
NH Materials Laboratory
Other independent test results:
Chemical Resistance Data From A Leading Epoxy Supplier.
The test was made using the company's most resistant epoxy and exposing fiberglass lab samples to 10% ethanol gas and regular unleaded gas as well as diesel and aviation gas.
The results for the ethanol gas showed a 10% loss in hardness and a 10-15% loss of compressive strength over a 16 week period. It is likely that the loss of hardness and strength would continue to fall at a similar rate over time. The unleaded gas, diesel, and aviation gas tests showed virtually no change.
Link to an informal test done by amateur boat builder:
http://egyptian.net/~raymacke/Cbnskif27.htm
http://egyptian.net/~raymacke/Cbnskif36.htm