Gasoila Water Finding Paste - Fuel Water Detection Gasoline, Diesel, Kerosene, Petroleum | 2.5 oz Tube | Quick Color Change | Reliable & Easy to Use | Ideal for Fuel Storage Tanks & Non-Ethanol Fuel

A simple, dependable way to confirm water in fuel

A sputtering outboard sent me down the path of checking the fuel, and that’s where the Gasoila water-finding paste earned a permanent spot in my kit. It’s a straightforward tool: smear the mustard-yellow paste on a gauging stick or clean dowel, dip it to the bottom of the tank, and if there’s free water present, the paste turns a vivid red where water meets fuel. No electronics, no calibration, no guesswork—just an immediate visual cue.

Over several weeks, I used the paste on a boat tank, a diesel storage tote, and a home heating oil tank. In each case, it did what I needed: tell me if free water had settled at the bottom, and roughly how much.

What it is and what it’s for

Water is heavier than hydrocarbon fuels and settles at the lowest point in the tank. The paste is designed to find that layer quickly. It’s intended for gasoline (especially non-ethanol gas), diesel, kerosene, and similar petroleum products. It’s not a test for dissolved moisture throughout the fuel; it’s for free water that’s separated and pooled.

Gasoila packages the paste in a 2.5 oz plastic tube. Compared to the old-school metal tubes you often see with similar products, the plastic tube is less prone to cracking, oozing, and sharp edges when tossed into a toolbox. The cap threads seal well, and I haven’t had leaks.

Setup and application

My routine looks like this:

1. Wipe a clean measuring stick, dipstick, or piece of PVC/wooden dowel.
2. Squeeze a small bead from the tube and spread a thin coat over the bottom 2–4 inches of the stick. A thin, even coat gives the cleanest read.
3. Lower the stick to the tank bottom and hold it there for about 10–15 seconds.
4. Withdraw and look for a color change. The yellow paste turns a distinct red wherever it touched water, creating a sharp interface line you can measure.

On a diesel tote that had sat through a damp spring, I saw a crisp 1/4-inch red band on the first dip. After draining the sump, I repeated the test and the red shifted to a faint trace, then disappeared entirely after a second drain. In the boat tank, it gave me quick confirmation that the issue wasn’t water that day, so I kept troubleshooting elsewhere.

Performance and speed

The color shift is fast—on the order of seconds—and highly visible. The red is saturated enough to read in low light, and it doesn’t smear into the yellow as long as you apply a thin layer. In cold weather (near freezing) the paste thickens but remains spreadable; the color change is still immediate. Warming the tube in a pocket for a minute helps if you’re working outside in winter.

The sensitivity is practical for maintenance: if there’s no free water, nothing turns red. If there is, even a shallow layer produces a clear line right at the interface. For routine checks, that’s exactly what I want: unambiguous yes/no, plus an estimate of depth.

Precision and limitations

• What it detects: free water at the bottom of the tank. It will not indicate dissolved moisture uniformly distributed in fuel. With ethanol-blended gasoline, small amounts of water can stay in solution; you’ll only see a red band after phase separation, when water and ethanol drop out together.
• Readability: the transition line is neat enough to estimate water depth to within a few millimeters on a smooth stick. If you’re measuring depth, mark your stick beforehand for quick reading.
• Interference: sediment and sludge can muddy interpretation. If you bring up a paste coated in brown or black fines, wipe and repeat with a gentler touch, aiming to contact the bottom without raking debris.
• Tank geometry: if the pickup or a baffle blocks the lowest point, you might not reach the true bottom with a straight stick. A flexible ruler or a thin PVC rod can help access sumps and low spots.

These aren’t flaws of the paste so much as realities of tank testing. Understanding them will save you from false assumptions.

Build and packaging details

The plastic tube is a small but meaningful improvement. It’s easier to meter a thin bead, the cap seals reliably, and it doesn’t dent. The paste itself has a smooth consistency—no gritty texture—and spreads evenly without clumping. Cleanup is easy: wipe your stick with a shop rag, then follow with a little mineral spirits if you want it spotless.

One quibble: my tube didn’t include an obvious manufacture or expiration date printed on it. Water-finding paste isn’t particularly fragile, but like any compound it can dry out or lose snap over time if stored poorly. I mark the purchase date on the tube with a paint pen and plan to replace it every couple of years or if the consistency changes. So far, after months of use and being stored in a truck box, the paste is still pliable and responsive.

Practical tips from use

• Use a thin coat. Thick globs can smear and make the interface fuzzy.
• Give it a full 10–15 seconds at the bottom. Yanking it out immediately can miss a shallow layer.
• Keep a dedicated “fuel stick.” A smooth, non-porous surface (poly or finished wood) shows the line cleanly and wipes off better than raw lumber.
• For cold-weather work, keep the tube in a pocket before use to maintain spreadability.
• Label your containers and tanks with test dates. If you’re managing multiple tanks, it’s easy to forget which ones you verified.
• After draining water, re-test. Seeing the red band shrink or vanish is a satisfying confirmation that you’ve actually fixed the problem.

Where it fits in a maintenance workflow

For me, this paste is a first-step diagnostic on anything that’s been sitting: boats, generators, tractors, and heating oil systems. Before swapping filters, bleaching tanks, or dosing with additives, I check for free water. If there’s none, I move on. If there is, I drain, re-test, and only then consider additives to handle residual moisture or microbial issues.

It’s also useful as a routine check right after fuel delivery to storage tanks. You’ll catch contaminated batches early, before water makes its way into equipment and causes corrosion, injector problems, or burner flame-outs.

How it compares conceptually

Functionally, most water-finding pastes promise the same outcome: a visible color change on contact with water. The differences that matter in daily use are consistency (does it spread evenly?), color contrast (is the red easy to see?), packaging durability, and performance in cold. Gasoila’s paste hits the mark in each area. The red is vivid, the paste is smooth, and the plastic tube is practical. I haven’t had it dry out at the tip the way some metal tubes do after a few openings.

Value and longevity

At 2.5 ounces, the tube goes a long way. A pea-sized bead covers an inch or two of stick, and most checks use just that much. Assuming occasional testing, a single tube can last years. Because there’s no ongoing calibration, strips, or sensors to replace, the running cost is effectively zero.

The bottom line

The Gasoila paste is the kind of low-tech tool I like best: simple, repeatable, and easy to trust. It turns a vague suspicion—“maybe there’s water in this tank”—into a clear answer in seconds, and it does so without mess or fuss. It excels as a first-line check across gasoline (especially non-ethanol), diesel, kerosene, and heating oil, and it holds up in both hot and cold conditions.

It’s not a Swiss Army knife; it won’t reveal dissolved moisture or microbial contamination. But as a quick detector for free water where it causes the most trouble—at the bottom of tanks—it performs exactly as advertised.

Recommendation: I recommend this paste for anyone who stores or uses hydrocarbon fuels—boat owners, small engine caretakers, farmers with diesel tanks, and homeowners with fuel oil. It’s inexpensive insurance against avoidable problems, gives an immediate and unambiguous read, and the packaging makes it cleaner to use than many alternatives. The only caveat is to be mindful of its scope: it finds free water, not all forms of moisture. Used with that understanding, it’s a reliable, practical addition to any fuel maintenance routine.