Gasohol E20 is a fuel created by blending base gasoline with ethanol of 99.5% purity at a ratio of 80% gasoline to 20% ethanol. The concept of using biofuels in Thailand originated from the foresight of His Majesty King Bhumibol Adulyadej the Great (Rama IX), who promoted energy security since 1985 by encouraging research into converting agricultural products like sugarcane and cassava into clean energy to reduce dependence on imported crude oil and support Thai farmers.
The push for commercial use was led by the Thai government in collaboration with the Ministry of Energy and oil distributors. At that time, Minister Piyasvasti Amranand spearheaded the establishment of excise tax structures to incentivize pricing E20 lower than other fuels. E20 was officially launched and sold in Thailand on 1 January 2008, with PTT and Bangchak being the first fuel providers to pioneer gas stations offering E20 dispensers.
Gasohol E20 is an alternative fuel blending base gasoline and ethanol in a specified ratio, with the following chemical composition and properties.
According to the Department of Energy Business standards, E20 must consist mainly of about 80% base gasoline and approximately 20% denatured ethanol by volume (allowing a slight variance between 19-20%).
The ethanol used must be denatured ethanol with at least 99.5% purity, free from water contamination (anhydrous) to prevent phase separation inside the fuel tank. Regarding chemical properties and octane rating, E20 in Thailand generally has an octane number no less than 95. Because ethanol itself has a high octane rating (around 107-113 RON), blending it with base gasoline improves the engine's knock resistance.
Heating value: Ethanol provides about 30% less heat energy than pure gasoline. Thus, E20 delivers slightly less energy than normal gasoline, potentially increasing fuel consumption (km/liter) by about 2-3% under similar driving conditions.
Reid Vapor Pressure: Adding ethanol alters the vapor pressure of the fuel, which must be controlled to ensure easy engine starts without vapor lock caused by fuel vapor blockage.
Additives: Besides gasoline and ethanol, other chemicals are added to maintain fuel quality, such as detergents to clean injectors and intake valves, and corrosion inhibitors to protect fuel system metals and rubber components from ethanol's moisture absorption and corrosive effects.
To safely use E20 in your vehicle, check your owner's manual and vehicle labels for clear indications.
Vehicles suitable for E20 use (no concerns) include:
Most new car models (generally from 2008 onwards) from almost all Thai automobile manufacturers (Toyota, Honda, Nissan, Mazda, Mitsubishi, etc.) have been tuned and equipped with fuel system materials compatible with E20 standards since then.
Vehicles with clear labels on the fuel cap stating "E20" or "E20 OK."
Owner's manuals specifying that the vehicle can use fuel blends containing up to 20% ethanol.
Eco Cars and newer models supporting E85 can also safely use E20 without issues.
Vehicles that should avoid using E20 include:
Older cars (before 2000) were not designed for high ethanol blends; rubber, seals, and plastic components degrade more quickly.
Some older European models from the early 2000s may only support up to E10 (Gasohol 91/95). Using E20 in these may trigger the Check Engine light.
Older motorcycles with carburetor fuel systems often face overheating, corrosion from ethanol, and hard starting in the morning.
Potential problems when using E20 in unsupported vehicles include:
Long-term damage may occur if E20 is used in vehicles not designed for it.
Fuel lines and rubber seals: Ethanol is more corrosive than regular gasoline, causing rubber hoses to swell, become brittle, or crack, leading to fuel leaks which increase fire risk.
Fuel pumps and injectors may clog or suffer corrosion damage due to alcohol exposure.
Corrosion inside fuel tanks, especially older steel tanks, as ethanol absorbs moisture promoting rust formation.
Engine performance may degrade; vehicles not tuned for E20 might experience rough idling, reduced acceleration, or increased fuel consumption due to improper heat values and air-fuel ratios.
The most reliable way to check your vehicle's compatibility is:
If unsure, consult your vehicle registration documents or check the Vehicle Identification Number (VIN) with the brand's service center for accurate confirmation.
For older vehicles on a budget, it's safer to use Gasohol 95 (E10) rather than moving up to E20.
Switching from Gasohol 95 to E20:
Switching fuel types from Gasohol 95 to E20 is straightforward since both are gasoline-ethanol blends differing only in ethanol content (10% vs 20%), which can be mixed without phase separation.
Here are recommended steps for a smooth transition for your engine.
Preparation before refueling (The Hardware Check):
First, ensure your vehicle supports E20 (usually indicated by a sticker on the fuel cap or in the manual). Engines designed for E20 have upgraded rubber hoses, gaskets, and seals resistant to ethanol corrosion, plus fuel injectors with appropriate flow rates.
Fuel mixing strategy (The Mixing Strategy):
You don't need to empty the tank completely (which risks sediment being drawn into the fuel pump). Two recommended methods: top up when you have half a tank of Gasohol 95 left by filling up with E20, resulting in about 15% ethanol (E15) in the tank, allowing gradual ECU adjustment.
Or use the fuel until the low-fuel warning appears, then fill with E20, causing the engine to adapt to the new fuel energy and octane levels quickly.
ECU learning phase (The Learning Phase): When E20 enters the combustion chamber, the following occurs:
The O2 sensor detects a change in Lambda values: burning E20, which has higher oxygen content, causes the mixture to become leaner.
Short Term Fuel Trim (STFT) immediately responds: the ECU increases fuel injection pulse width within seconds to maintain a Lambda of 1.
Long Term Fuel Trim (LTFT) adjustment: after driving 10-20 km, the ECU records the increased injection in permanent memory, ensuring more accurate starts and open-loop operation according to the new fuel type.
Additional recommendations during transition:
Watch for slight engine hesitation in the first 5-10 km after refueling; this is minimal in new cars and due to recalibration.
Morning starts: ethanol evaporates less easily at low temperatures, so starting may take 1-2 seconds longer, which is normal for high ethanol fuels.
Keep the fuel system clean: ethanol's solvent properties may loosen deposits in older tanks, possibly clogging fuel filters during the first 1-2 tanks; check for reduced acceleration and consider filter replacement if needed.
Long-term parking: if leaving your vehicle unused for over two weeks, keep more Gasohol 95 than E20 in the tank, as higher ethanol content absorbs moisture more readily, potentially harming the fuel pump and injectors over time.
Usage precautions:
Because E20 contains more alcohol than standard 91 or 95 octane fuels,
Corrosion: some vehicles made before 2008 may not have fuel system materials resistant to 20% ethanol's corrosive effects.
Moisture absorption: if left unused for over 1-2 months, ethanol can absorb moisture and cause phase separation in the tank, damaging the fuel system.
Arkom Ruamsuwan
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