We're taught to expect nothing but reliability from Japanese engines, and these popular cars have failed to hit the mark.

Generally, Japanese automakers have a reputation for producing reliable and affordable cars. Japanese car manufacturers like Toyota and Honda are among the most reliable car brands in the world. On top of that, JDM engines are popular among gearheads for their ability to withstand incredible amounts of power with aftermarket tuning. But nothing is perfect.

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Throughout Japanese automotive history, some engines were far worse than average. Plagued with many dependability issues, their respective brands eventually abandoned them in favor of more reliable engines. But this wasn't before the engines and cars bankrupted their owners with expensive maintenance and repair bills.

Whether it's due to poor build quality, substandard engineering, or underwhelming power figures, these are the 10 worst Japanese car engines ever made.

Subaru is among the few automakers that entered diesel engine production a bit late. They, therefore, applied a different approach to retain the trademark boxer engine layout. Unfortunately, this turned out catastrophic. Early first-generation models had a DPF problem due to excessive oil soot formation that needed replacing sooner than later.

When owners tried to fix this problem with aftermarket performance kits, the high-pressure direct fuel injection system would make holes in the pistons. While Subaru fixed these issues upon warranty, owners found the engine expensive to live with after their warranties expired.

The 3VZ-E debuted in 1988 in the 4Runner, Toyota T100, and Toyota Pickup. Considering the size of the automobiles it powered, the 3.0-liter V6 engine's 150hp and 180lb-ft of torque was pitiful. The fact that the engine wasn't dependable didn't help matters much.

The engine had serious head gasket problems arising from the combination of a cast iron block with an aluminum cylinder head and would often overheat. Add in cylinder head cracks, and connecting rod bearings wear, and you realize how pretty unreliable of an engine it was. Knocking sounds and a rise in oil consumption would be the final symptoms of a dying engine at only 180,000 miles.

If there were an award for the worst car engine ever built, the 13B-MSP Renesis would be a strong contender. Performance-wise, the engine couldn't compete with the 13B-REW that came before it since Mazda prioritized fuel economy.

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Leaking apex seals are the engine's weakest link, turning the Mazda RX-8 into an oil and gasoline guzzler, usually after 40,000 kilometers. Other problems relate to ignition coils, catalytic converter failure, and engine flooding . On top of the high maintenance and repair costs, this motor requires a rotary engine specialist.

The 1MZ-FE (1993 to 2007) had the potential to be a top-tier engine. Toyota implemented it in several vehicles and even made a TRD supercharger kit available for the Camry, Solara, and Sienna. However, many drivers later learned the engine was bad due to several issues.

Any slight disrespect for routine service and oil changes led to the dreaded sludge buildup, dooming many engines early. Also, overheating would lead to head gasket failures and cracked aluminum heads - which are costly to fix. The result was a class-action lawsuit and a settlement covering roughly 2-5 million Toyota and Lexus vehicles (1997-2002).

The Mitsubishi 4G54B (1978 to 1992) was a very big 4-cylinder engine that came in the Starion, Pajero SUV, L200 pickup truck, and some Chryslers. Despite its enticing on-paper profile, its tunability left much to be desired.

Fuel injectors positioned behind the throttle body had sketchy fuel distribution, and its 2.6-liter displacement was not helped by the tiny OEM turbocharger. The difficulty of wringing out more power was compounded by limited aftermarket support. And to make matters worse, owners and tuners eventually discovered that it was prone to head gasket problems.

The Nissan QR-series engine replaced the mediocre KA engines and the iconic SR, but the 2.5-liter variation (QR25DE) was the most problematic. The 2.5-liter QR25DE engine is basically identical to the QR20DE except for a few details. The integrated catalytic converter on Sentra models suffered from poor ECU tuning.

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While the Altima models didn't experience the same issue, they suffered from problematic piston rings that led to excessive oil and water consumption. This problem ultimately triggered a recall campaign. Additionally, there was an issue with loose screws in the intake plenum. The outcome was catastrophic for the cylinder walls if the screws found their way into the combustion chamber.

Produced between 1986 and 1992, the 7M-GTE powered the Soarer Z20 and the Supra A70. The 3.0-liter turbocharged engine was Toyota's top-performance engine before the 1JZ-GTE replaced it. Supposed to put the Supra on the map as Toyota's best sports car, reliability issues dented its success.

The inline six-cylinder engine suffered from failed head gaskets (turbo models) which destroyed its reputation. Another common problem is rod knock. While the 7M-GTEU racing version produced up to 580hp on the tap, you'd rather get the bulletproof 1JZ or 2JZ if you want 800-1000+hp from a Japanese engine.

The EJ Engine series succeeded the Subaru EA engine and became the mainstay of the brand's engine line, with all engines featuring 16-valve horizontal flat-fours. You can get the EJ series engine in either naturally-aspirated or turbocharged form, with power ranging between 96 and 320hp. While owners report head gasket failures in the EJ Engine series, the 2.5-liter EJ25 boxer engine experiences the most problems.

According to Consumer Reports, models produced between 2001 and 2009 still have unreliable head gaskets despite Subaru's effort to fix the problem in 1999. This problem lies in the horizontal engine design, as cooling fluids tend to pool adjacent to the head gasket when the engine isn't running. Although it costs about $1,500 for head gasket repair, the labor to pull out the engine takes a big chunk of the repair bills.

Introduced in 1998, the 1.8-liter 1ZZ-FE engine mainly powered front-wheel drive cars such as the Celica GT and Corolla and a few rear-wheel drive vehicles like the Lotus Elise and MR2 Spyder. Unlike the 1.8-liter 7A-FE engine it replaced, the 1ZZ-FE utilized a die-cast aluminum cylinder block.

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The 1ZZ-FE never earned much buyer respect, and Toyota replaced it with the 2ZR-FE in 2007. It was underwhelming from a performance perspective, producing 120-140hp. On top of that, earlier engines produced before 2005 consumed excessive oil. This problem was a design flaw in the engine's oil piston rings. Although Toyota revised and improved these engines in 2005, the 1ZZ-FE's reputation was already damaged.

One of the reasons why Japanese engines have above-average durability is the tendency to use timing chains to reduce maintenance. However, not all engines fitted with timing chains are reliable, especially Nissan's 1.5/1.8-liter QG engines.This is due to the wear-prone piston rings that annoy drivers with an immoderate appetite for excessive oil consumption.

In the worst-case scenario, this consumption hits 1.5-l/1000km, which is extreme considering the engine's oil sump holds less than 3 liters. This makes the 1.5/1.8-Liter QG engine a ticking time bomb. Although Nissan replaced the faulty engines with new ones upon warranty, there's little you can do after the warranty expires besides expecting high maintenance and repair bills.

Sources: Dsportmag, Autowise, Toyotanation, YouTube, Carvertical

Dennis Kariuki is a tech enthusiast who writes for Hotcars.com. Previously, he wrote for the.car .He likes covering the marriage between technology and cars. Besides that, he is big f1 fan. After working tirelessly through the week, you can be sure that on Sundays he is most likely enjoying and following motorsports events.