How to Convert Propane RV Generator to Diesel: Complete Fuel System Guide for Safe Installation

The Quick Answer

Yes, you can safely fuel a diesel generator without starving your main engine, but you're absolutely right to be concerned about fuel starvation. Simply teeing off the main fuel line is not recommended and could indeed starve your engine or generator during high demand because it creates competition for fuel at the same pickup point. The proper solution is to install a dedicated fuel transfer system with either a separate fuel pickup tube in your tank or a fuel polishing system that draws from and returns to the main tank. Most successful conversions use a small 12V transfer pump (like a Facet or Carter unit) sized according to your generator's fuel consumption requirements and pressure specifications that feeds a small day tank or directly supplies the generator with proper fuel return lines.

What's Causing This

Your concern about fuel starvation is well-founded because diesel engines and generators have very specific fuel flow requirements. Your main engine's fuel system is designed for its specific consumption rate and pump capacity. When you add a generator to the same fuel supply without proper planning, you create several potential issues.

The primary problem is that both the engine and generator will be competing for fuel from the same source. During heavy loads - like running the generator while driving up hills - both systems could demand more fuel than the main fuel pump or pickup can deliver. Additionally, diesel generators typically need a fuel return system to prevent overheating and maintain proper pressure, which a simple tee connection doesn't provide.

Another issue is that diesel fuel systems rely on consistent pressure and flow. Air bubbles or fuel starvation in one system can affect the other, potentially leaving you stranded or without power when you need it most.

Tools You'll Need

For a professional diesel generator conversion, you'll need several specialized tools and components. A 12V fuel transfer pump rated for diesel (see manufacturer specs for appropriate models) is essential, along with appropriate fuel-rated hose, fittings, and clamps. You'll also need basic hand tools including wrenches, screwdrivers, and wire strippers.

Electrical components include a fuel pump relay, inline fuse holder, and marine-grade wiring. For fuel system work, you'll need a fuel pressure gauge, fuel line disconnect tools, and thread sealant rated for diesel fuel. Safety equipment is crucial - have a fire extinguisher nearby, work in a well-ventilated area, and keep absorbent materials on hand for spills. Ensure proper grounding of all fuel system components to prevent static electricity buildup, be aware that diesel fuel vapors can be explosive, and never smoke or use open flames when working on fuel systems.

Depending on your chosen approach, you might need a tank sending unit tool, hole saw for additional tank fittings, or components for a day tank system. Many RVers also install a fuel flow meter to monitor consumption and ensure adequate supply to both systems.

Step-by-Step Fix

Start by determining your fuel supply strategy. The most reliable approach is installing a separate fuel pickup in your main tank, positioned away from the engine pickup to prevent interference. However, fuel tank modifications typically require professional certification and specialized equipment in most jurisdictions due to safety regulations, so this work should be performed by a qualified technician.

Install your 12V transfer pump in the fuel line between the tank and generator, mounting it in an accessible location but away from heat sources. Wire the pump through a relay connected to the generator's ignition or run circuit so it only operates when the generator is running - this prevents unnecessary fuel circulation and potential issues. Consult your generator's wiring diagram for the appropriate signal wire and ensure the system includes a manual override switch for initial fuel line priming and system bleeding. Connect the pump to run off your house batteries with proper fusing and use marine-grade connections.

Create a fuel return system from the generator back to the tank. This is critical for proper diesel generator operation and prevents fuel from overheating in the lines. The return line should be properly sized according to generator specifications and enter the tank separately from the main return to avoid creating turbulence that could affect the engine's fuel pickup.

Before testing, properly bleed and prime the fuel system according to generator manufacturer procedures to remove all air from fuel lines. Test the system thoroughly before putting it into regular service. Run the generator under various loads while monitoring fuel pressure and flow. Check that your engine starts and runs normally after generator operation. Many installers recommend adding a fuel/water separator and additional filtration in the generator fuel line since generators are often more sensitive to fuel quality than engines.

When to Call a Pro

Call a professional if you're not comfortable working with fuel systems or if your RV has complex fuel tank access. Any work involving cutting into fuel tanks or major modifications to fuel lines should be done by someone with proper certifications and insurance. This is especially important for newer RVs where warranty considerations come into play.

Professional installation is also recommended if you're dealing with multiple fuel tanks, complex routing, or if you want to add sophisticated fuel management systems. A qualified technician can properly calculate fuel flow requirements, ensure all connections meet safety standards, and provide documentation that may be required for insurance purposes.

Additionally, if you experience any fuel system problems after installation - like hard starting, fuel contamination, or pressure issues - it's better to have a professional diagnose the problem rather than risk damage to expensive engine or generator components. Most RV service centers have experience with generator conversions and can ensure your system meets both safety and performance requirements.