If you own a Ram, Charger, or Challenger, you've likely spent some sleepless nights worrying about your 5.7 hemi mds lifters and whether that faint clicking sound under the hood is actually a sign of impending doom. It's one of those topics that can spark a three-hour debate at a local car meet, with everyone from backyard mechanics to professional tuners weighing in on why these specific components seem to have such a reputation for failing. The 5.7 Hemi is, by all accounts, a fantastic engine with a lot of soul, but the Multi-Displacement System (MDS) adds a layer of complexity that has left more than a few owners scratching their heads and reaching for their wallets.
The reality is that while most Hemi engines will run for 200,000 miles without a hiccup, a vocal minority deal with lifter issues that can eventually eat the camshaft. Understanding why this happens and what your options are can save you thousands of dollars and a whole lot of frustration down the road.
What's Actually Going On Inside There?
To understand why 5.7 hemi mds lifters act up, you have to look at what they're designed to do. In a standard engine, a lifter is a pretty simple hydraulic component that sits between the camshaft and the pushrod. Its job is to take the rotational motion of the cam and turn it into the vertical motion that opens the valves.
With the MDS-equipped 5.7, things get a bit more technical. The MDS lifters are "collapsible." When the engine's computer decides you don't need all eight cylinders—like when you're cruising on the highway at 65 mph—solenoids redirect oil pressure to these specific lifters. This pressure disengages a locking pin inside the lifter, allowing it to compress without actually moving the pushrod. The valves stay closed, the cylinder stops firing, and you theoretically save some gas.
It's a clever bit of engineering, but it introduces more moving parts into a high-heat, high-friction environment. When those internal pins or the needle bearings in the lifter roller start to give out, that's when the trouble begins.
The Infamous Hemi Tick
We can't talk about 5.7 hemi mds lifters without talking about "the tick." If you start your truck in the morning and hear a metallic click-click-click that follows the RPM of the engine, you're probably experiencing one of two things.
The "good" news is that it might just be a broken exhaust manifold bolt. This is incredibly common on the 5.7 Hemi. The bolts snap, the manifold warps slightly, and you get an exhaust leak that sounds suspiciously like a mechanical tap. If the sound goes away once the engine warms up and the metal expands to seal the leak, you've dodged a bullet.
The "bad" news is when that tick is constant, regardless of engine temperature. This usually indicates that the needle bearings inside one of the lifter rollers have seized up. When the roller stops rolling, it starts dragging across the camshaft lobe. Imagine a lathe slowly carving away at a piece of metal—that's what a seized lifter does to your cam. Once the cam lobe is flat, the engine will start misfiring, and at that point, you're looking at a full teardown.
Why Do They Fail in the First Place?
There are a few schools of thought here, and most experts agree it's a combination of factors. One of the biggest enemies of 5.7 hemi mds lifters is actually long periods of idling. Because of the way the Hemi's oiling system is designed, the lifters and camshaft lobes rely heavily on "splash lubrication" from the crankshaft spinning. When the engine is just sitting at an idle, there isn't as much oil being flung around the top end as there is when you're actually driving. This can lead to the lifter rollers getting "dry," which eventually causes the bearings to fail.
Another factor is oil choice. The MDS system is incredibly sensitive to oil viscosity. Chrysler recommends 5W-20 for a reason; the solenoids and the tiny passages in the MDS lifters need that specific weight to function correctly. If someone puts in a much thicker oil thinking they're "protecting" the engine, they might actually be starving the lifters of the flow they need to stay lubricated and pressurized.
Maintenance Habits That Might Save Your Engine
If you haven't experienced any issues yet, there are things you can do to keep your 5.7 hemi mds lifters happy. First and foremost: don't skimp on oil changes. It sounds like basic advice, but because the MDS system relies on clean oil and precise pressure to move those internal locking pins, even a little bit of sludge or debris can cause a lifter to hang up.
Many Hemi enthusiasts swear by high-quality synthetic oils with a good dose of molybdenum (moly), which acts as a friction modifier. While it's not a magic cure, keeping that friction as low as possible on the roller bearings is always a good idea.
Also, try to avoid excessive idling. If you're sitting in a parking lot for thirty minutes with the AC on, your lifters aren't getting the best lubrication. It's better to shut it down or get it moving. Some people even choose to disable the MDS feature using an electronic tuner. While this doesn't physically change the lifters to a non-MDS style, it stops the constant cycling of the pins, which some believe extends the life of the components.
The Fork in the Road: Repair or Delete?
If you find yourself in the position where a lifter has definitely failed, you have a big decision to make. You can either replace the failed components with new factory 5.7 hemi mds lifters, or you can do what's known as an "MDS Delete."
Replacing them with stock parts is usually the cheaper route in the short term. You swap the lifters, put in a new camshaft (if the old one was chewed up), and you're back on the road with your fuel economy intact. However, you're essentially putting the same system back in, which means it could technically happen again another 80,000 miles down the road.
The MDS delete is the "permanent" fix. This involves swapping out the collapsible MDS lifters for solid, non-MDS lifters (often the ones used in the 6.1 or the 392 Hemis). You also have to replace the MDS solenoids with plugs and swap the camshaft for a non-MDS version. Finally, you'll need a custom tune to tell the engine's computer to stop looking for the MDS system. It's a more involved and expensive process, but it removes the failure point entirely. Most guys who plan on keeping their trucks for the long haul or who want to add a more aggressive cam eventually go this route.
Don't Panic, But Stay Informed
It's easy to get onto the internet and feel like every single 5.7 Hemi is a ticking time bomb, but that's just not the case. There are millions of these engines on the road doing just fine. However, being aware of how 5.7 hemi mds lifters work—and why they sometimes don't—makes you a more prepared owner.
If you hear a new sound, don't ignore it. Catching a lifter issue before it ruins the camshaft can be the difference between a $1,000 repair and a $4,000 engine overhaul. Keep the oil fresh, keep the idling to a minimum, and listen to what your engine is trying to tell you. These Hemis are legendary for a reason, and with a little bit of extra attention to the valvetrain, they can be as reliable as anything else on the road.