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Results of Fuel and Fiberglass Gas Tank Tests

Soon after the Long Island Sound area of New York switched to gas mixed with ethanol, BoatUS 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, BoatUS 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 BoatUS 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

Fiberglass Tank and Residue Analysis

Analysis of a piece of fiberglass tank (sample 1) and residue from tank (sample 2). Samples were examined using stereomicroscope and Fourier Transform Infrared Spectroscopy (FTIR). Sample 1 showed that the inside section of the tank has begun to erode. Portions of the resin material are flaking off in sheets, exposing the actual fiberglass webbing. Additionally, the resin on the inside of the tank had tiny granular particles adhering to the sheets that were delaminating from the inside surface. Examination of the residue (sample 2) showed sheets of resin-like material, with a similar appearance as the material flaking off the tank. The sheets observed in sample 2 also had tiny granular particles adhering to the surface as viewed with the aid of the microscope.

Analysis of the resin and granular material from sample 1 and the residue and granular material in sample 2 showed they had a similar composition. This indicates that the residue in sample 2 is coming from the erosion of the tank material (sample 1).

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.

Ethanol and Fiberglass Tanks

Test Results are Discouraging. Meanwhile, Problems With Fiberglass Tanks May be Spreading

The January 2006 issue Seaworthy reported on several engines in the Long Island Sound area that seemed to have been badly damaged when fiberglass tanks that had been filled with ethanol-enhanced gasoline started to fail. Some of the tanks had begun leaking. Seaworthy has since received dozens of additional complaints, which, again, were mostly from the Long Island Sound area.

New York state recently switched their oxygenated gas mix from MTBE (an ether) to a blend of 10% ethanol. There have also been three complaints of the problem from California, which mandates a 5.6% blend of ethanol, as well two reported problems from the Great Lakes. Ethanol blends of up to 10% have been used in he Midwestern states for a many years.

The reports are all remarkably similar — a black sludge coats intake manifolds and builds up on intake valves, which soon destroys the engine. Most of the reports still involve fiberglass tanks made before the mid-80’s by notable manufacturers such as Hatteras, Bertram, and Chris Craft. We’ve even received reports from owners of small outboard powered boats that had been using portable fiberglass tanks.

Fiberglass/Ethanol Test Results

BoatUS sponsored lab test on two badly deteriorated fiberglass tanks to help confirm that the problems were indeed being caused by ethanol. The results, as expected, were not encouraging; though the report is full of hard to pronounce chemical names and expensive sounding equipment, the bottom line is that the tests indicate that two fuel tanks have undergone aggressive degradation—losing up to 40% of their strength. The report goes on to say that there is “resin softening and loss of adhesion between fiber and resin, evidenced by a moderate loss in both strength and stiffness.”

A separate test, this one on ethanol-enhanced gasoline taken from a fiberglass tank, revealed the presence of styrene, a component of polyester resin that is used to make fiberglass fuel tanks. According to the EPA, styrene should not be present in gasoline. Another lab test of the black stuff on a valve showed what appeared to be degraded polyester.

An independent test done by New Hampshire Materials Laboratory seems to indicate that ethanol reacts with chemicals in the resins and causes a reaction much like osmotic blistering, only at a much faster rate. The report says that ethanol dissolves uncured phthalates in the fiberglass (the same chemical that can cause osmotic blistering of a boat’s hull), which then pass through the engine’s filters and get deposited on the intake components.

Finally, chemical resistance data from a leading epoxy supplier showed that even epoxy can be attacked by ethanol. 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 and it’s likely that the loss of hardness and strength would continue to fall at a similar rate. The unleaded gas, diesel, and aviation gasoline tests, none of which contained ethanol, showed virtually no loss of strength.

What to Do?

Many boaters have made the decision to replace what were thought to be superior fiberglass gas tanks with aluminum tanks (tank replacement is not covered by insurance). Seaworthy has talked to resin manufacturers who say that there are resins that resist ethanol, but simply coating a tank with one of these resins is not likely to work, since the tank has to be thoroughly cleaned and prepped on the inside and the resins have to be specially cured.

The good news is that the requirement for oxygenated fuel has been dropped by the EPA this year. The bad news is that the recent energy bill introduced by the federal government calls for billions of gallons of ethanol to be used in the nation’s fuel supply. And since there is a tax incentive for ethanol, more states are planning to use gasoline. (New Jersey, for one, will begin switching over about the time this issue is mailed.)

What can an owner of a gas-powered boat with fiberglass tanks do? There doesn’t appear to be any quick fixes or magic additives that can slow the degradation of fiberglass tanks. Tank replacement is the only sure cure. In the meantime, owners of these boats are urged to install gasoline vapor alarms.


BoatUS Editors

Contributor, BoatUS Magazine

Award-winning BoatUS Magazine is the official publication of Boat Owners Association of The United States. The magazine provides boating skills, DIY maintenance, safety, news and more from top experts.