Fixing the Factory Duramax Flaws: Known LML Trouble Spots
Fixing Factory Flaws: Known LML Duramax Trouble Spots
When General Motors introduced the 6.6L LML Duramax for the 2011–2016 models, it had impressive horsepower and increased torque over its predecessor. However, ask any experienced diesel mechanic about LML Duramax flaws, and they’ll tell you the same thing: the factory engine has structural, thermal, and mechanical weak points that can leave you stranded or cost thousands in repairs.
At D&J Precision Machine, we’ve built our reputation on expert machining and race-winning Cummins engines. Now, we’re bringing our diesel expertise to the Duramax platform with our new 2011–2016 6.6L LML Duramax Long Block Engines, specifically engineered to eliminate those known factory failure points.
3 Known Weak Points of the LML Duramax Engine
1. Head Gasket and Cylinder Head Failures
- The Factory Issue: Under heavy towing, elevated cylinder pressures, or high heat cycles, stock LML head bolts stretch. This leads to blown head gaskets, warped heads, and coolant consumption.
- Our Machining Solution: We resurface every head, recut valve seats, and install upgraded stem seals. For our Precision Plus long block, we upgrade to ARP head studs combined with Tier 1 Multi-Layer Steel (MLS) head gaskets to provide dramatically higher clamping force and eliminate head gasket failure.
2. Crankshaft and Gear Retention Issues
- The Factory Issue: The stock LML relies on a friction-fit press arrangement for key components. Over time, especially in high-stress applications, gear slip on the crankshaft, camshaft, or oil pump can throw off engine timing or cause a sudden loss of oil pressure.
- Our Machining Solution: Every D&J LML long block features keyed crankshaft and camshaft retention. To ensure total peace of mind, our Precision Plus build also includes a pinned oil pump, preventing gear movement or slippage regardless of load.
3. Oil Temperature Control and Thermal Stress
- The Factory Issue: Engine oil temperatures can spike quickly during heavy pulls, causing thermal breakdown, reduced oil life, and increased wear on bearings and turbochargers.
- Our Machining Solution: We integrate an upgraded L5P oil cooler on our Precision Plus package, providing superior heat rejection to keep oil temperatures controlled.
D&J LML Duramax Engines: Choose Your Build
We’ve engineered two 6.6L LML Duramax long blocks designed for everyday drivers, work trucks, and high-performance tow rigs.
| Feature / Upgrade | Essentials LML Long Block ($9,499.99) | Precision Plus LML Long Block ($13,499.99) |
|---|---|---|
| Target Application | Daily drivers & tow rigs needing a solid remanufactured baseline | High-torque towing, performance builds, & turn-key installations |
| Crank & Cam Retention | Keyed Crankshaft & Camshaft | Keyed Crankshaft & Camshaft + Pinned Oil Pump |
| Head Sealing | Tier 1 Head Gaskets & Refreshed Heads | ARP Head Studs + Tier 1 MLS Head Gaskets |
| Thermal Management | OEM-Spec Thermal Package | Upgraded L5P Oil Cooler |
| Valvetrain & Accessories | Core block + refreshed heads with new valves | Includes: Rocker assemblies, valve covers, intake manifold, harmonic balancer, flex plate/flywheel, and mounting hardware |
| In-House Testing | RMC ETS Compression & Cooling Testing | Compression, Cooling, + Oil Pump Pressure & Volume Testing |
| Warranty | 24-Month / 100,000-Mile | 24-Month / 100,000-Mile |
The D&J Advantage: In-House Precision & Testing
We don't just assemble generic parts. We measure, machine, and test every long block in-house at our Cambridge, Ohio facility.
- Controlled Assembly: Critical dimensions, bearing clearances, and deck surfaces are blueprinted and verified at every step.
- RMC ETS Testing: Every completed engine undergoes RMC ETS testing to verify cylinder compression and cooling system integrity before shipping. Precision Plus builds also undergo live pressure testing for oil pump flow and volume.
- Backing Our Work: Both engine packages come backed by our 2-Year / 100,000-Mile Warranty.
Ready to Upgrade Your LML?
Whether your stock engine suffered a failure or you’re building a truck that you can depend on for the long haul, D&J Precision Machine has the solution.