Ensuring Reliability: How to Maintain Your Hemi After Mds Removal with OEM or Aftermarket Parts

Understanding MDS Removal and Its Impact on Your HEMI

The Multi-Displacement System (MDS) was introduced by Chrysler to improve fuel economy by deactivating four of the eight cylinders under light load. While effective for EPA numbers, many enthusiasts disable or remove the system to eliminate reliability concerns, improve throttle response, and unlock the engine’s true potential. However, once MDS is removed, the engine’s dynamics change. The camshaft, lifters, and oiling system are affected, and maintenance strategies must adapt accordingly. Whether you choose OEM or aftermarket components, a well-informed approach is essential for long-term reliability.

MDS removal typically involves installing a non-MDS camshaft, non-MDS lifters, and often a custom tune to disable the system electronically. Some owners also replace the valley pan and oil control hardware. The result is a simpler, more robust valvetrain that eliminates the known failure points of MDS lifters—collapse, wear, and catastrophic engine damage. But with this modification comes the responsibility of tailored maintenance.

Why Remove MDS? Common Failure Modes

Before discussing maintenance, it helps to understand why many HEMI owners opt to delete MDS:

• Lifter collapse: MDS lifters are hydraulic and prone to failure, especially with extended oil change intervals or low oil pressure.
• Camshaft wear: Failed lifters can gouge cam lobes, requiring expensive cam and lifter replacement.
• Oil dilution: MDS deactivation can increase fuel dilution in oil, accelerating wear.
• Hesitation and noise: MDS engagement transitions can feel sluggish and produce unwanted vibration.

By removing MDS, you eliminate these failure modes, but you also lose the fuel economy benefit. The trade-off is a more reliable, responsive engine—provided you adapt your maintenance habits.

Maintenance Strategies After MDS Removal

Oil and Lubrication: The Foundation of Reliability

After MDS removal, your HEMI relies on the camshaft and lifters operating under constant pressure. Because MDS lifters are replaced with solid or non-MDS hydraulic lifters (often from Hellcat or aftermarket brands), the oil requirements shift. Use a high-quality full synthetic oil with a viscosity that matches the new cam and lifter clearances—typically 5W-30 or 5W-40. Many tuners recommend Pennzoil Ultra Platinum or Amsoil Signature Series. Change oil every 3,000-5,000 miles, not the factory 8,000-10,000 mile interval, to prevent sludge and maintain proper additive levels. Also consider installing a high-volume oil pump to ensure adequate pressure at idle and high RPM.

External reference: Amsoil synthetic oil recommendations for high-performance HEMI applications.

Cooling System Upgrades

Removing MDS can increase engine heat because the engine now runs on all eight cylinders more often. The factory cooling system may be adequate for stock power levels, but if you’ve also added a performance cam or higher compression, consider upgrading the radiator, thermostat, and cooling fan. A 170°F or 180°F thermostat helps keep temperatures stable. Monitor coolant levels regularly and flush the system every 30,000 miles. Use a high-quality coolant like Zerex G-05 or Mopar OAT. Overheating is a common complaint after MDS delete, but it can be prevented with proactive parts selection.

Ignition System: Spark Plugs and Coils

With MDS removed, the engine’s firing order and load patterns change. Standard copper-core spark plugs may wear faster. Upgrade to iridium or platinum plugs (e.g., NGK 92145 or Champion 9409) and gap them per your camshaft manufacturer’s specs. Replace ignition coils if they are aged—aftermarket options like MSD or ACDelco provide better dwell and longevity. Inspect spark plug wires if your HEMI uses a separate coil-on-plug setup. Proper ignition is critical to avoid misfires that can damage the catalytic converters.

Exhaust System and Tuning

MDS removal often goes hand-in-hand with aftermarket exhaust. A performance cat-back system (e.g., Borla, Corsa, or Mopar Performance) reduces backpressure and lets the engine breathe. But more importantly, the engine control unit (ECU) must be tuned to disable MDS and adjust fuel maps accordingly. A custom tune from a reputable shop like DiabloSport or HP Tuners is essential. Without the tune, the ECU will still try to engage MDS, causing drivability issues and potential engine damage. The tune also recalibrates the transmission shift points for the new power curve.

External reference: DiabloSport tuning solutions for HEMI MDS delete.

Valve Train Inspection and Adjustment

Non-MDS lifters may require periodic lash adjustment depending on the cam type. Hydraulic flat tappet lifters (common in aftermarket kits) are self-adjusting, but solid roller lifters need manual checks. Follow the cam manufacturer’s break-in procedure—first 20 minutes at varied RPM, then change oil and filter. After 500 miles, inspect the lifters for proper rotation and check for any abnormal wear. Using a bore scope through the spark plug hole can reveal carbon buildup or valve damage. Early detection prevents major repairs.

OEM vs. Aftermarket Parts: What Works Best?

OEM (Mopar) Parts

Original Equipment Manufacturer parts from Mopar are designed to the exact specifications of the HEMI. For MDS delete, Mopar offers non-MDS camshafts (e.g., Hellcat cam) and non-MDS lifters that are direct replacements. Pros: guaranteed fit, OEM quality control, quiet operation, and often a warranty. Cons: higher cost, limited performance options, and the Hellcat cam may not optimize low-end torque for daily driving. OEM parts are an excellent choice if you want a reliable, factory-like experience without the tuning complexity of aftermarket cams.

Aftermarket Performance Parts

Aftermarket companies like Comp Cams, Killer B Motorsports, Texas Speed & Performance, and Briley Manufacturing offer complete MDS delete kits with upgraded cam profiles. Benefits include tailored lift and duration for specific power goals, lighter components that reduce reciprocating mass, and often lower cost than OEM. Some kits include new lifters, pushrods, springs, and retainers for a complete valvetrain upgrade. However, aftermarket parts may require more meticulous installation and tuning. Choose reputable brands with verified dyno results and clear instructions.

External reference: Comp Cams HEMI MDS delete camshafts for detailed specs.

Recommendation: Hybrid Approach

Many experienced builders combine OEM oil pump, timing chain, and tensioner with an aftermarket cam and lifters. The oil pump is a critical component—OEM Mopar oil pumps are reliable, while aftermarket high-volume pumps can stress the oil pan gasket. For most street-driven HEMIs, an OEM oil pump paired with a quality aftermarket cam and lifters provides the best balance of reliability and performance. Always replace the timing chain and tensioner during MDS delete, as they are wear items.

Common Post-Delete Issues and Troubleshooting

• Check Engine Light (CEL): Often due to incomplete tuning. Ensure the PCM is flashed with MDS disabled and all O2 sensor monitors are reset. Use a scan tool to clear pending codes.
• Rough idle: Caused by incorrect cam timing or vacuum leaks. Verify that the camshaft phaser is locked properly (if variable valve timing is retained). Inspect intake gaskets and PCV hoses.
• Oil leaks: Common at the valley pan if the MDS solenoid block is removed. Use a new Mopar valley pan gasket and apply correct torque sequence. Aftermarket valley pan covers often seal better than OEM.
• Noisy valvetrain: May indicate improper lifter preload or wrong pushrod length. Measure pushrod length after cam installation with a checking tool. Use Smith Brothers or Manton pushrods for exact lengths.
• Reduced fuel economy: Expected after MDS removal. However, if fuel consumption drops dramatically, check for exhaust leaks or a stuck open thermostat.

Long-Term Maintenance Schedule

After the initial 500-mile break-in, adopt the following schedule for a post-MDS-delete HEMI:

Interval	Task
Every 3,000 miles	Oil and filter change (synthetic). Inspect valve cover gaskets for leaks.
Every 15,000 miles	Replace spark plugs, check ignition coils. Inspect serpentine belt and tensioner.
Every 30,000 miles	Coolant flush. Inspect radiator and fan clutch. Check camshaft lobe wear via oil analysis.
Every 50,000 miles	Replace timing chain, tensioner, and guides (if not already done). Consider water pump replacement.
Annually	Inspect exhaust system for leaks. Test battery and charging system. Update ECU tune if new components added.

Conclusion: Building a Reliable Post-MDS HEMI

Removing the Multi-Displacement System from your HEMI is a proven step toward better reliability and performance, but it requires a shift in maintenance philosophy. Regular oil changes with high-quality synthetic oil, upgraded cooling components, and a professional tune form the bedrock of a trouble-free engine. Whether you choose OEM or aftermarket parts depends on your goals—factory-like simplicity or maximum power. By following the guidance in this article, you can ensure your HEMI runs smooth, strong, and dependable for tens of thousands of miles.

For further reading, consult the Hemi MDS delete resource guide and explore aftermarket cam profiles from Texas Speed & Performance.