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Fuel system deposits, which decrease engine performance and efficiency, form when heavy hydrocarbons in fuel are partially oxidized. In other words, the hydrogen in the fuel burns and creates water in the exhaust, while the carbon doesn’t fully combust and instead sticks to engine surfaces as elemental carbon.
Hot surfaces, such as the backs of valves and the piston crown, are most prone to deposit accumulation. Deposit formation is often a surface phenomenon where liquid fuel undergoes pyrolysis — another fancy word for when hydrogen burns away and carbon clumps together to form deposits. Deposits on the back of valves reduce intake and exhaust efficiency, while deposits on the piston crown cause it to run hotter. Carbon buildup around piston ring lands can prevent proper sealing and lead to cylinder bore scoring.
Bottom line? Deposits are bad news!
The role of fuel control
The first step in reducing deposits is good fuel control. Modern fuel-injected engines regulate the fuel-air ratio precisely to achieve near-complete combustion — meaning all carbon should ideally become CO2, and all hydrogen should become H2O.
However, under extended high-load conditions (like towing a trailer up a mountain), engines inject extra fuel to keep critical components cool. Unfortunately, excess fuel means excess carbon at a time when surface temperatures are high — prime conditions for deposit formation. Frequent short trips can also lead to deposits from fuel condensing on engine surfaces.
Finding the right solvent
The trick to cleaning up these unwanted deposits is using the right solvent. I was thinking about this the other day when I parked my car under a tree, which promptly dropped several globs of sap onto my hood.
“What solvent do I need? Hot water and a sponge?” Just smeared it around. “Soap?” Useless. “Goo Gone?” Nope. “WD-40?” Still no luck. Time for an internet search! Turns out hand sanitizer (which is primarily made of bioethanol) dissolves tree sap. Who would’ve guessed?
Now, think about cleaning your kitchen stove or a greasy mechanical part — what do you reach for? A degreaser! Degreasers dissolve oils (carbon-heavy compounds) and leave no residue. Bioethanol is an excellent degreaser because it dissolves carbon-dense components and promotes complete combustion of both hydrogen and carbon, preventing deposit buildup in the first place.
Cleaning vs. lubrication
While gasoline on hot engine surfaces can contribute to deposit formation, it also provides lubrication for key parts like valve seats and piston rings. Adding bioethanol to fuel reduces deposits, but it can also reduce lubrication. To compensate, engine manufacturers have improved valve seat materials, piston ring designs, and cylinder bore finishes in modern engines to ensure durability while keeping deposits in check.
The verdict
Yes, bioethanol reduces fuel system deposits — and the higher the bioethanol percentage, the greater the effect, and engine design enhancements compensate for reduced lubrication. Indeed, modern engines achieve excellent durability and resistance to deposits, even under extended high-load conditions, while running on high-bioethanol fuel blends.
So, if you’re looking for a fuel ingredient that helps keep your engine clean, bioethanol’s got your back. And just in case you park under a tree, keep a bottle of hand sanitizer in your glovebox!
