Does MDS Delete Really Fix Hemi Cam/Lifter Failure?

Summary

David from Hemi Garage Hacks tests how removing the Multi-Displacement System (MDS) affects oil delivery to Hemi lifters and cam rollers. His main conclusion is that an MDS delete appears to improve lubrication in this low-speed test, but it does not eliminate camshaft and lifter failures.

Test setup and observations

• The engine runs on a pushrod tester at about 700 rpm and roughly 30 psi oil pressure. It is warm; the block temperature is later reported at about 150°F.
• With MDS operating normally, all eight cylinders run until MDS is activated. The system uses oil pressure to collapse its special lifters, stopping the valves from operating. It also disables fuel injection and ignition for those cylinders.
• The MDS cylinders are 1, 4, 6, and 7.
• David removes the four MDS solenoids and plugs their openings to compare oil flow. Several initial rubber plugs are forced out, creating small oil “geysers.” This indicates that open or poorly sealed ports affect pressure and oil flow, making this part of the comparison difficult to interpret.
• Better-fitting plugs hold more reliably, though one still leaks or falls out. David emphasizes that increased pressure in a passage does not necessarily mean more oil reaches the lifter roller.
• He observes that some lifters receive more oil than others. In his visual comparison, oil delivery to the tested rollers is generally better with the MDS system removed.

Full MDS-delete test

• For the final configuration, David removes both the MDS solenoids and the MDS lifters, replacing them with regular hydraulic lifters.
• The engine runs with all cylinders active at approximately the same oil pressure—about 30 psi.
• He again sees more oil reaching the lifter rollers than in the MDS configuration, although some lifters still appear to receive relatively little lubrication.
• He interprets the results as suggesting that MDS can restrict or reduce lubrication to the tested rollers under these conditions, and that removing it improves oil delivery.

Main lesson and limitations

• David says an MDS delete may help by improving lubrication, but it is not a complete fix for Hemi camshaft and lifter failures.
• Based on his shop experience disassembling thousands of engines, he also sees failures in vehicles that came from the factory without MDS. He does not provide comparative failure-rate data and notes that most vehicles on the road may have MDS, making raw counts difficult to compare.
• The test is primarily a visual, low-speed assessment—not a quantified measurement of oil volume or a controlled study of long-term failures. Plug leaks and ejections also complicate some comparisons.
• David plans to investigate whether reaming the pushrods and their sockets could improve lubrication. This is presented as future work, not as a proven solution.

Speakers and sources featured

• David — presenter from Hemi Garage Hacks; conducts the test and shares his observations and shop-based perspective.
• No other speakers or external sources are featured in the subtitles.