A YouTuber attempting to build a fully 3D printed rocket engine has tested an unusual solution to one of the biggest challenges facing plastic rocket components. Heat.

The project, created by YouTuber Mr. More Gooder, explores whether a rocket engine printed with a standard FDM printer could withstand combustion by circulating water through internal channels built directly into the engine walls.

Conventional plastic rocket engines tend to fail almost immediately after ignition because the combustion chamber and nozzle rapidly reach temperatures high enough to soften or melt common printing materials. Instead of changing materials, the builder attempted to remove heat before it could destroy the structure.

The design uses a hollow double-walled architecture in which water flows continuously through internal channels, while propane and air mix separately before combustion. The concept is broadly similar to regenerative cooling techniques used in conventional liquid rocket engines, although implemented here with consumer-grade printing methods and plastic materials.

Water cooling improved survival but exposed new limits

According to the build video, the first engine versions lacked any cooling and failed almost instantly after ignition. The combustion chamber softened rapidly, and the structure deformed within seconds as exposed plastic sections began melting.

The builder then redesigned the engine using a two-wall structure. Water circulated between the inner wall exposed to combustion gases and the outer structural shell using a small pump connected through printed adapters.

Before firing, the system was pressure-tested for leaks. Ignition used two-bolt electrodes that generated an electrical arc, but later tests switched to a grill lighter after the electrodes themselves began bending from heat.

The revised engine performed noticeably better. During testing, the water-cooled combustion chamber remained intact and operated longer than previous versions.

However, another issue quickly appeared. Sections lower in the nozzle that were not cooled began to overheat and sag while molten plastic dripped from the engine outlet. “The cooled section held up well, but the other section, not so much,” the creator explained in the video.

Fully cooled version ran but developed internal leaks

To address the failure point, the builder developed a fully water-cooled version printed as a single piece with cooling channels covering all areas exposed to combustion gases.

Initial results again appeared promising, and the engine operated longer while maintaining structural stability. The test ended when a leak formed in the inner wall, allowing coolant to enter the combustion area and extinguish the flame.

Post-test analysis suggested the issue may be linked to a more fundamental material limitation. Standard FDM plastics conduct heat poorly, meaning the inner wall must reach very high temperatures before heat can radiate outward toward the coolant.

Thinner walls could improve heat transfer but would reduce structural strength and pressure resistance. The project also highlighted another challenge for any future flight-capable design. Mass.

Water reservoirs, pumps, and plumbing increase weight, potentially reducing payload capacity and overall performance. Although the experiment did not produce a fully functioning plastic rocket engine, it demonstrated that active cooling significantly improves survivability and may provide a path for further development.

The creator concluded that the concept still has potential but requires further refinement and invites suggestions for future iterations.