Moeller Marine Fuel Tanks & Vent Cap Guide

Portable outboard tanks that look similar can have different capacities, footprints and hose-outlet arrangements. Moeller’s Ultra3, 6BOW and Ultra6 designs are not the same shape. Compare the actual tank dimensions and the original fuel cap before selecting a replacement.

Choose by shape and usable space

Ultra3 portable fuel tank3 US gal (11.35 L)
17 × 9 × 9¾ in unpacked

Compact rectangular tank

Compare part 620003LP

6BOW portable fuel tank6 US gal (22.71 L)
19 × 16½ × 11 in unpacked

Wide bow-style tank

Compare part 620040LP

Ultra6 portable fuel tank6.5 US gal (24.60 L)
21¼ × 13½ × 10 in unpacked

Long, narrow Ultra6 tank

Compare part 620049LP

All dimensions are manufacturer-listed unpacked exterior measurements. Allow additional clearance for connections and handling.

Do not confuse fuel capacity with tank footprint. The six-gallon 6BOW is wider than the six-and-a-half-gallon Ultra6. The Ultra6 also features a rotating fuel-withdrawal connection. Match the shape, not just the volume.

Moeller capacity and dimensions chart

MPN	Component	Capacity	Unpacked dimensions (L × W × H)
620003LP	Ultra3 portable fuel tank	3 US gal (11.35 L)	17 × 9 × 9¾ in
620040LP	6BOW portable fuel tank	6 US gal (22.71 L)	19 × 16½ × 11 in
620049LP	Ultra6 portable fuel tank	6.5 US gal (24.60 L)	21¼ × 13½ × 10 in
305994-10	Two-stage replacement vent cap	Replacement cap	Match original fill neck

The cap is a replacement component, not a standalone fuel tank. Moeller’s current documentation lists the cap as a specified factory-style replacement for compatible Moeller/Tempo portable tanks.

Before ordering a portable fuel tank

Measure the actual tank storage area and allow clearance for fuel hose, cap and lifting access.
Choose 620003LP for the 3-gallon Ultra3 shape, 620040LP for the 6BOW design, or 620049LP for the 6.5-gallon Ultra6 only when suitable for the vessel.
Check the original fuel pickup connection and the outboard manufacturer’s hose and fitting requirements.
For cap 305994-10, compare the original fill neck and tank family, and follow Moeller’s two-stage venting and pressure-relief instructions.
Secure the tank as specified and follow marine gasoline safety rules; do not install a tank in an unsuitable enclosed space.

Vent caps are safety components. Moeller 305994-10 uses a two-stage vent and pressure-management design. Use the correct cap for your tank and follow its instructions; do not substitute an unverified ordinary cap.

Compare Moeller fuel tanks and the replacement cap

Open each exact NewRVParts listing for product details and online availability.

Moeller portable fuel tanks

Moeller 620003LP ultra3 portable fuel tank catalog product photo

Moeller 620003LP — Ultra3 portable fuel tankThe Ultra3 is Moeller’s compact three-gallon low-permeation portable tank. Check the available floor space and clearance for the cap, outlet and fuel line.View product and availability

Moeller 620040LP 6bow portable fuel tank catalog product photo

Moeller 620040LP — 6BOW portable fuel tankThe 6BOW layout is intended for bow placement on compatible inflatable boats and dinghies. Its wider 16½-inch footprint differs from the Ultra6.View product and availability

Moeller 620049LP ultra6 portable fuel tank catalog product photo

Moeller 620049LP — Ultra6 portable fuel tankThe Ultra6 holds 6.5 gallons and has a rotating fuel-withdrawal assembly to help align the fuel hose. It is not the same shape as the 6BOW.View product and availability

Two-stage replacement fuel cap

Moeller 305994-10 two-stage replacement vent cap catalog product photo

Moeller 305994-10 — Two-stage replacement vent capMoeller’s two-stage cap includes an audible sealing click, tether and pressure-management features. The manufacturer lists it for specified Moeller and Tempo-style portable tanks; match the original cap and neck.View product and availability

Related marine fuel parts

Need outboard primer-bulb hoses and a comparison with other portable tank sizes? See the Attwood tank and fuel-line guide.

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Moeller Portable Fuel Tanks: Ultra3, 6BOW & Ultra6 Guide