Military vehicle maintenance has gotten complicated with all the conflicting advice flying around forums and Facebook groups. As someone who’s been wrenching on everything from M35s to HMMWVs for close to twenty years, I learned everything there is to know about keeping these unique machines running. Today, I will share it all with you.
These trucks present challenges that differ significantly from civilian automotive work. Multi-fuel engines, 24-volt electrical systems, and specifications designed for actual combat conditions require specific knowledge and approaches. If you’re coming from working on regular cars, there’s a learning curve—but it’s manageable once you understand the philosophy behind these systems.
The Multi-Fuel Engine
Probably should have led with this section, honestly. The LDT-465 multi-fuel engine that powered the M35 “Deuce and a Half” represents an engineering approach that civilian vehicles never bothered to adopt. This beast can run on diesel, JP-4 jet fuel, kerosene, or even gasoline—basically any combustible liquid fuel you could scrounge up in a war zone.
Multi-fuel capability comes from a unique fuel injection system that’s unlike anything you’ve seen on civilian diesels. Where your typical diesel has precisely calibrated injectors that demand specific fuel, the multi-fuel system uses adjustable injectors and a fuel heater designed to accommodate wildly different fuel properties. Operators adjust the system for fuel type using a simple selector—elegant in its simplicity.
Maintenance requires understanding this flexibility. That’s what makes working on these engines both interesting and challenging. Injector timing, fuel heater operation, and combustion chamber deposits all vary depending on what you’ve been feeding it. Many civilian owners run JP-8 or regular diesel exclusively, which simplifies maintenance considerably but doesn’t exercise the full system capability. Nothing wrong with that approach if availability isn’t a concern.
24-Volt Electrical Systems
Most military vehicles use 24-volt electrical systems rather than the 12-volt systems you’re used to from civilian cars. This provides real advantages for starting heavy engines in cold weather, radio operation, and powering equipment—but it definitely complicates component sourcing when something breaks.
The 24-volt system typically uses two 12-volt batteries wired in series. Some components genuinely need the full 24 volts, while others tap the batteries at 12 volts for convenience. Understanding which circuits use which voltage is critical—I’ve seen people fry components by making incorrect connections, and it’s an expensive mistake.
Civilian replacements for electrical components require careful selection. Lights, gauges, and accessories must match the 24-volt requirement or you’ll be buying them twice. Some owners convert their systems to 12-volt to simplify parts sourcing, but this sacrifices original specifications and may significantly affect vehicle value for collectors.
Hydraulic and Pneumatic Systems
Military vehicles often feature hydraulic power steering, brake assist, and winch systems that civilian trucks of the same era rarely had. These require specific fluids and maintenance intervals that you need to follow. The military specification MIL-PRF-2104 covers lubricants; civilian equivalents exist but must meet the same performance requirements—don’t just grab whatever’s on sale.
Air brake systems, common on larger military vehicles, demand regular inspection and maintenance that many car guys aren’t familiar with. Moisture accumulation, compressor condition, and brake adjustment all require ongoing attention. Many states also require air brake certification for drivers, so check your local requirements before you take delivery.
Finding Parts and Expertise
Military vehicle parts come from surplus dealers, specialty suppliers, and increasingly from civilian equivalents with compatible specifications. Online forums provide invaluable guidance on interchangeable parts—the collective knowledge there has saved me countless hours and dollars.
Finding mechanics experienced with military vehicles can be genuinely challenging. That’s what makes the community so important. Some military vehicle clubs maintain lists of knowledgeable shops in various regions. Many owners develop their own expertise out of necessity—and honestly, these vehicles were designed for maintenance by soldiers with basic training, not factory-certified technicians. If you can follow a technical manual and swing a wrench, you can maintain these trucks.
