Stop the Drip: Common Causes and Expert Fixes for Ford Lehman 120 HP Fuel Leaks
The Ford Lehman 120 HP diesel engine is renowned as a reliable workhorse for many classic trawlers and cruising vessels. However, like any seasoned marine engine, it can occasionally develop a fuel leak. A diesel leak is more than just a mess—it’s a serious fire hazard and an environmental concern. If you’ve spotted a tell-tale puddle of diesel in your bilge, it’s time for an immediate investigation.
As the marine engine experts in the Kemah area, we at Yes Centers know exactly where to look when a dependable Ford Lehman 120 starts to weep.
Where Does the Ford Lehman 120 HP Typically Leak Fuel?
The good news is that many Ford Lehman fuel leaks are caused by simple, fixable issues related to fittings and components on the low-pressure side of the fuel system. Here are the most common culprits:
1. Loose Bleed Screws and Banjo Bolt Washers
This is often the easiest and most overlooked source of a slow leak. The Ford Lehman’s fuel system requires periodic bleeding, especially after a filter change.
The Cause: If a bleed screw on the fuel filter housing or the injection pump (often a Simms pump) is not re-tightened sufficiently, or if the copper crush washer underneath is old or damaged, it can weep diesel fuel under engine vibration.
The Fix: A simple snugging of the screw might solve it, but the most reliable fix is to replace the copper crush washer with a new one. This ensures a proper, fuel-tight seal.
2. High-Pressure Injector Return Lines
The diesel fuel that doesn’t get injected into the cylinders is routed back to the tank or filter via low-pressure return lines, often utilizing small rubber hoses.
The Cause: These rubber hoses degrade over time due to heat and exposure to diesel fuel. They can crack, become brittle, or loosen where they attach to the injector nozzles or the main return rail, leading to a visible leak on the engine.
The Fix: Inspect and replace any cracked or hardened return lines immediately. This is a crucial maintenance item on any older diesel engine.
3. Leaking Fuel Lift Pump
The fuel lift pump (or mechanical fuel pump) is mounted on the side of the engine block and is responsible for drawing fuel from the tank and pushing it to the fuel filters and injection pump.
The Cause: The diaphragm inside the pump can fail, or the gasket where the pump meets the engine block can deteriorate, allowing fuel to leak externally or, in rare cases, into the engine oil (causing a rising oil level).
The Fix: A lift pump that is leaking should be replaced entirely. While repair kits exist, the peace of mind and reliability of a new or professionally rebuilt unit is worth the investment.
4. Failed Injector Pump Seals
The heart of the fuel system, the injection pump, uses various seals and gaskets.
The Cause: Internal seals within the injector pump (especially on Simms or CAV/Lucas DPA pumps) can wear out, causing fuel to leak externally and pool in the bilge, or internally, leading to fuel dilution of the pump’s lubricating oil.
The Fix: This is a job best left to certified diesel mechanics. The pump often needs to be removed and taken to a specialist shop for proper overhaul and calibration.
Need Expert Marine Diesel Help in the Kemah Area?
Don’t let a slow drip turn into a critical problem. A diesel fuel leak is a serious maintenance issue that requires prompt, professional attention.
At Yes Centers in Kemah, TX, our experienced marine technicians specialize in all aspects of diesel engine repair and diagnostics, including the venerable Ford Lehman 120 HP. We offer convenient dockside service across Kemah, Clear Lake, Galveston Bay, and the surrounding areas within a 30-mile radius, meaning we come to your slip to get your engine fixed right.
Contact us today for professional service that keeps your classic diesel running reliably and safely.
Yes Centers 828 Marina Bay Dr, Kemah, TX 77565 Phone: +1 281-538-9377
