How to Winterize Your RV’s Fuel the Right Way

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Fuel does not stay fresh forever. Gasoline begins to oxidize in a few months, forming sticky varnish and gum that can clog carburetors, injectors, and fuel filters. Diesel faces its own problems: as it ages, it can oxidize and darken, while water condensation inside the tank creates an environment where bacteria and fungus (yes, fungus) can grow. Those microbes leave behind sludge that blocks filters and can damage pumps.

Temperature swings during winter storage make the situation worse. Warm daytime air carries moisture that condenses on the cool metal walls of a tank at night. Over time, that water settles to the bottom of the tank or mixes with ethanol in gasoline, increasing the risk of rust in steel tanks and poor performance later.

The bad news? Forgetting to treat your fuel is one of those winterizing mistakes many Rvers tend to make.

The good news is that protecting your fuel isn’t complicated. With the right stabilizers and a little attention while you winterize your RV, you can keep your RV’s fuel system clean and ready when you roll out next year.

Gasoline Engines

Start by treating the motorhome’s main fuel tank. Add a stabilizer designed for ethanol-blended gasoline, such as Star Tron or Sta-Bil, before you fill the tank. Adding the stabilizer first helps it mix thoroughly as the fuel goes in. Fill the tank nearly full to reduce the amount of moist air inside and lower the chance of condensation and rust if the tank is steel.

Once the tank is treated and full, run the engine for 10 to 15 minutes. This pulls the stabilized fuel through the lines, pump, and injectors or carburetor, so every part of the system is protected while the RV sits through winter.

💡Tip: Don’t forget your gas-powered generator! Use the same stabilizer you added to the main tank. After filling and treating the fuel, start the generator and let it run for about 10 to 15 minutes so that stabilized fuel reaches its carburetor or injectors. For owners who want to go further, Onan suggests a deeper prep: disconnect the fuel line, run the generator dry, draw stabilizer directly into the carburetor, and run it dry again. This extra step is optional and more involved than most people need, in my opinion.

Diesel Engines

Diesel needs its own kind of care. Start by adding a diesel-specific stabilizer such as Power Service Diesel Fuel Supplement. This product slows oxidation and helps keep cetane levels stable during storage.

If your RV will sit for many months or has had microbial growth in the past, add a biocide such as Biobor JF. Diesel can develop bacteria or fungus when water collects in the tank, and a biocide keeps that from spreading.

Fill the tank completely after adding the treatment. A full tank leaves less room for moist air, which cuts down on condensation and the chance of rust in steel tanks. Once treated and full, run the engine and any diesel-powered generator long enough for the stabilized fuel to reach the lines and injection system.

Engine Care Beyond Fuel

If you can reach your RV during winter, starting the engine and generator once a month does more than keep fuel fresh. Running them under load for 30 to 45 minutes coats internal parts with oil, keeps seals flexible, moves coolant to reduce sediment buildup, and helps generator windings stay dry.

💡Tip: wait for a milder day, about 20°F or warmer, and let the oil, not just the coolant, reach normal operating temperature before shutting down.

If your RV will stay parked and untouched for the whole season, it’s still worth changing the oil and filters beforehand. Old oil holds moisture and acids that can corrode engine parts during storage.

Wrapping Up

Fuel often gets overlooked when people prepare an RV for winter. Yet untreated gasoline or diesel can quietly turn into a spring headache, clogging filters, rusting tanks, or causing a generator that refuses to start. Adding the right stabilizer, keeping the tank full, and circulating treated fuel through engines and generators is usually all it takes.

For those who can visit their RV during the off-season, a short monthly run keeps moving parts lubricated and helps prevent internal corrosion. A fresh oil change before long storage is a smart final step. With a little attention now, you’ll avoid costly fuel-system problems and start next season with confidence.