HOW TO TEST ETHANOL CONTENT
"E85" at the pump legally ranges from E51 to E83 by season and region. If you blend to a target or run a dedicated tune, that 30-point swing matters — and a two-minute test with water settles it.
WHAT YOU NEED
A graduated ethanol test tube — a few dollars, lives in the glovebox. Grab a tester on Amazon. A narrow graduated cylinder from a kitchen-scale kit works in a pinch.
THE TEST
- Water to the line. Fill the tube with water to a marked line — say 2 ml.
- Fuel to the top line. Add pump fuel up to the fill mark — say 10 ml total.
- Shake and settle. Cap it, shake hard for 15–30 seconds, then let it sit a few minutes.
- Read the line. Ethanol leaves the gasoline and bonds with the water, so the separation line rises. The rise, divided by how much fuel you added, is your ethanol percentage.
Example: water at 2 ml, filled to 10 ml (so 8 ml of fuel), line settles at 8.8 ml → it rose 6.8 ml → 6.8 ÷ 8 = E85. Line doesn't move at all? That's E0.
SKIP THE ARITHMETIC
The blend calculator has this built in — open TEST YOUR FUEL, punch in your three readings, and one tap drops the result straight into the blend math as your E85 pump's actual content or your tank's current mix.
FAQ
How accurate is this?
Within a few percent. It ignores the small volume shrink when water and ethanol mix — the same simplification the printed scales on commercial testers make. For blending, plenty. For live-tune precision, run an ethanol content sensor.
When should I test?
Any fill that matters (dyno day, track day), any new station, and always during seasonal changeover months — that's when the pump swings hardest.