V8-6-4 Engine

10 Worst Car Engines That Made Mechanics Cringe

Engines are the beating heart of automobiles, but not all engines are created equal. While some have become legends for their power, efficiency, or innovation, others have earned a different kind of reputation—one they’d rather forget. 

As car manufacturers strive for excellence, they occasionally stumble upon designs plagued by reliability issues, lackluster performance, or engineering missteps. These engines, each with its own story, have gained infamy among automotive enthusiasts and owners alike.

The Infamous Iron Duke Engine: A Heavyweight Underachiever

Iron Duke
Image Credit: WikiCommons.

The Iron Duke engine stands out as a notorious example of underpowered and inefficient engineering in recent history. Crafted entirely from iron, its durability came at a hefty price—it was excessively weighty for an inline-four engine. General Motors’ decision to install this powerhouse in vehicles like the Pontiac Fiero, the Firebird, and notably, the Chevrolet Camaro, left enthusiasts scratching their heads. The idea of a classic ‘muscle car’ boasting just over 90 horsepower was almost comically disappointing. Despite its durability, the Iron Duke engine remains etched in memory as one of the most lamentable engines of its time.

GM’s Terrible V8-6-4 Engine: A Groundbreaking Concept Gone Awry

V8-6-4 Engine
Image Credit: WikiCommons.

GM’s V8-6-4 engine, touted as groundbreaking for its variable displacement technology, unfortunately, fell flat in execution. The concept of adjusting displacement based on need seemed promising, yet the reality was far from ideal. The engine’s internal sensors struggled to keep pace with its dynamic changes, resulting in erratic performance that caused the car to lurch and falter. Despite the engine’s supposed ability to gauge the required cylinders and fuel-air ratios, the end result was a miserable misfire, tarnishing the engine’s reputation and leaving a lasting legacy of disappointment.

The LF9 Diesel V8 Engine: Oldsmobile’s Troubled Legacy

LF9 Diesel V8
Image Credit: Hemmings.

The LF9 diesel V8 engine from Oldsmobile earned a reputation as nothing short of a vehicular nightmare. Diesel V8 engines, historically, weren’t known for ease of maintenance, and this diesel iteration, a direct conversion of Oldsmobile’s 5.7-liter gasoline V8 architecture, became a catalyst for the United States’ disinterest in diesel engines for nearly four decades.

The litany of issues plaguing the LF9 engine was relentless. From pervasive leaks in head gaskets and oil pans to corroded fuel injector pumps and instances of water contamination in fuel, the engine’s faults were abundant. Its propensity to crack and seize regularly further sealed its notoriety, ultimately eroding Oldsmobile’s reputation and leaving a stain on its history.

The Iconic RX-8’s Renesis 13B Wankel Rotary Engine: A Legacy of Woes

Renesis 13B
Image Credit: WikiCommons.

Despite inheriting the legacy of the revered RX-7, the Mazda RX-8 failed to uphold its predecessor’s sterling reputation. Much of the blame for the RX-8’s notorious reliability issues falls on the Renesis 13B Wankel rotary engine housed under its hood.

Regrettably, the Renesis motor emerged as one of the most notoriously unreliable engines in automotive history. Owning an RX-8 often meant frequent visits to the mechanic rather than enjoying its performance on the road. Excessive oil consumption, engine flooding, catalytic converter failures, and problematic apex seals were just a few of the myriad problems plaguing this engine. These issues turned the RX-8 ownership experience into a never-ending headache, tarnishing its legacy within the automotive world.

BMW’s 5-Liter S85 Motor: A Titan’s Stumble

BMW 5-Liter S85
Image Credit: WikiCommons.

Even giants falter, as evidenced by BMW’s 5.0-liter S85 engine. Initially introduced beneath the hood of the M6 in 2005, this engine turned what could have been an exceptional car into one to avoid at all costs.

The S85 engine’s Achilles’ heel was its insatiable appetite for rod bearings. Issues extended beyond that; even the throttle actuators in the M3 variant were notoriously prone to failure. Coupled with the SMG transmission, the S85 motor exacerbated problems in models like the M5 and M6. Any BMW model equipped with the S85 engine or derivatives thereof became a cautionary tale, steering buyers away from the pre-owned market due to its notorious unreliability.

Škoda’s 1.2 HTP Engines: Volkswagen’s Troublesome Redesign

Škoda's 1.2 HTP
Image Credit: WikiCommons.

Produced between 2002 and 2007, Škoda’s 1.2 HTP engine struggled due to its weak hydraulic tensioner within the timing system, leading to frequent instances of the chain jumping teeth. Infamous for its voracious appetite for both oil and fuel, this power mill also suffered from prevalent burnt valve issues.

In an attempt at a comprehensive redesign, the Volkswagen Group implemented new chains and tensioners to rectify the persistent problem. However, this effort led to a new set of issues. The throttle butterfly valves became problematic, compounded by faulty EGR valves, further tarnishing the engine’s reliability despite attempts to salvage its troubled history.

Subaru’s Troubled 2.0 and 2.5-Liter Boxer Engines: A Government Intervention

2.5-Liter Boxer
Image Credit: WikiCommons.

In recent years, Subaru’s 2.0- and 2.5-liter naturally-aspirated boxer engines have gained infamy due to their alarming oil consumption issues. Witnessing brand-new engines burning oil straight out of the dealership raised serious concerns, prompting government intervention. Subaru ultimately acknowledged a defect in the piston rings of their 2011–15 vehicles, resulting in a negligence lawsuit. To address this, the brand had to reimburse owners for repair costs and extend warranties. Nationwide, dealerships replaced countless short blocks, cementing this engine’s status as one of the worst in recent automotive memory.

Volkswagen’s FSI Engine: A Disastrous Evolution

Volkswagen's FSI Engine
Image Credit: Shutterstock.

In the early 2000s, Volkswagen embarked on a quest for ‘more advanced and efficient’ engines to power their lineup, leading to the introduction of the FSI engine. Unfortunately, these new engines didn’t live up to their promises of efficiency and compatibility.

The most significant issue plaguing VW’s FSI engine stemmed from carbon deposits accumulating in the intake system and valves. Compounding these problems were malfunctioning sensors that incurred exorbitant costs for repairs or replacements, along with unreliable timing chains.

From the onset of production, the FSI engine proved terribly unreliable. Experiencing four-figure repair bills on small commuter cars was simply unacceptable, solidifying this engine’s reputation as one of the worst, leaving owners grappling with its unreliability and costly maintenance.

The Yugo 55’s Engine: An Unreliable Relic

Yugo 55's Engine
Image Credit: WikiCommons.

The Yugo 55’s 1.1-liter carbureted engine stands as one of the most unreliable and underpowered engines to grace American roads. Generating a mere 55 horsepower, this Serbian vehicle claimed the title of the slowest car sold in the country.

However, its faults extended far beyond its lackluster performance. Sporting a timing belt prone to snapping and causing catastrophic engine failure, the engine demanded exclusive use of premium gasoline, adding to its inefficiency. Even the carburetor contributed to its woes. The rejoicing of gearheads across America was palpable when the EPA announced the marque’s failure to meet exhaust emissions standards, leading to the brand’s exit from the USA in 1992.

BMW’s N47 Diesel Engine: A Modern Marque Misfire

BMW N47 Diesel
Image Credit: WikiCommons.

BMW’s N47 diesel engine, produced between 2007 and 2012, found itself marred by significant issues, earning its place on this ignominious list. Notorious for substantial timing chain wear, the engine’s demise often seemed inevitable.

The rapid wear of the timing chain caused considerable collateral damage. While older BMW models typically present good deals in the used car market, any vehicle equipped with the infamous N47 diesel four-cylinder unit is best avoided, offering a cautionary tale of reliability concerns associated with this engine.

Author: Madison Cates

Title: Managing Editor


Research journalist, Freelance writer, Managing editor

  • Expertise: automotive content, trending topics.
  • Education: LeTourneau University, Bachelors of Science in Business Administration.
  • Over 400 articles and short news pieces published across the web.

Experience: Madison Cates is a journalist located in the great state of Texas. She began writing over eight years ago. Her first major research piece was published by the Journal of Business and Economics in 2018. After growing up in a household of eight brothers and a dad who was always restoring old Camaros, she naturally pivoted her freelance career into the automotive industry. There, she found her passion. Her experience paved the way for her to work with multiple large corporations in automotive news and trending topics. Now, she now finds her home at Wealth of Geeks where she proudly serves as Managing Editor of Autos. Madison is always down to geek out over the latest beautiful cars on the market, and she enjoys providing her readers with tips to make car ownership easier and more enjoyable.

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