A number of HEMI engines today use cylinder deactivation systems like MDS, which is short for Multiple Displacement System, to improve fuel economy. If you have a vehicle with a V8 engine, MDS will turn off four of the eight cylinders without you noticing a significant reduction in power or speed. This deactivation of half your engine’s cylinders reduces pumping losses, which, in turn, increases fuel efficiency. Simply put, fewer cylinders operating means less air being pumped in and out, which means less energy being used. This is what causes the bulk of fuel savings with an MDS.
However, for this system to work effectively, the MDS lifters will need to function correctly. While various things can cause the MDS to malfunction, the most common cause is contaminated oil. When contaminants block the lube circuit, the MDS lifter may not be able to engage and disengage effectively. This can result in the system not switching to the fuel-saving model, which, in turn, means you don’t benefit from any possible fuel savings that this sort of technology can provide.
The easiest way to avoid problems with the MDS is to perform regular oil changes and take your car for timely maintenance checks to identify any potential issues with the MDS early on, rather than waiting until a complete MDS lifter failure has occurred. If the MDS has already failed, you might be able to swap it out for new lifters, especially if your powertrain warranty is still active.
