Defining what is the worst car engine is trickier than it might sound. There are terrible engines that could be more reliable or don’t have the best power output.
Then, some engines should never have gone into the cars they went into. Think of the DeLorean DMC-12 as one example, a sports car with an engine that does not befit a sports car.
This list will attempt to go through some of the worst car engines ever. Many of these were simply terrible designs, while others were terrible in their own unique way.
Oldsmobile Diesel
It is only now that diesel engines’ inefficiencies are beginning to shine through. But in the 1970s, Oldsmobile’s diesel engines were some of the worst as the company tried to mimic the success of diesel engines in Europe.
Oldsmobile used its 350 ci V8 as the basis for a diesel, creating a reinforced block and slapping new diesel heads onto it. Sadly, power was low at just 120 hp, and the resulting engine was loud, produced thick smoke, and would result in blown head gaskets.
Jaguar V12
We can hear the screams as we mention the Jaguar V12 on a list of bad engines. But the reality was that, while a fine piece of machinery, Jaguar’s V12 had problems. In the E-Type/XK-E, issues were relatively minor, but it was in later models, such as the XJ-S and XJ-12, where the big problems lay.
The cooling system needed to be better. It was not helping that it was very complicated for mechanics to fix should an issue arise. Keeping a Jaguar V12 running in tip-top condition can quickly become a costly exercise, so be wary of that should you own a V12 Jag.
Cadillac Northstar V8
The Northstar V8 was Cadillac’s first dual-overhead cam engine, and it helped the American manufacturer catch up with some of its rivals in Europe and Japan. Sophisticated and powerful, the Northstar V8 was a potent engine.
Early engines had 295 hp, but in the XLR-V Roadster and the STS-V, this increased to 469 hp. However, despite its sophistication, the Northstar V8 had some significant problems. The most problematic of these was the blown head gaskets installed in the engine with a single-use product that also stretched during the installation process. However, stretching would occur during the car’s use, leading to coolant leaks, overheating, and, ultimately, to the blown gaskets.
Ford 1.0-liter EcoBoost
The latest generation of Ford EcoBoost engines are some of the best on the market. The EcoBoost V6 under the hood of the Ford GT was the best of the bunch. But from 2018 to 2022, the small EcoSport SUV also had an EcoBoost engine, with the car built by Ford in India.
The EcoSport could have been a better car, but the engine was much worse. The belt that drove the oil pump would often wear out exceptionally quickly or loosen themselves up. The issue became so concerning that the NHTSA would open an investigation to prevent a similar problem in North America.
Volkswagen / Audi 2.5 TDI V6
The 2.5 TDI V6 engine is widely used in older Volkswagen Passats and the second-generation Audi A6. Despite both cars being good, solid daily drivers, flaws with the V6 engine are well documented. The construction of the cylinder head meant that the camshafts suffered and would wear out rapidly.
That issue is down to oil changes needing to occur more regularly. Audi and the broader Volkswagen Group umbrella were unaware of this, and it was only when owners worked it out for themselves that the problem became widely known. Changing the oil more frequently will work around the problem; however, that isn’t something consumers should have to do.
Triumph V8
The 1960s and 1970s were an up-and-down time for British motoring. Some exceptional cars came out of the country, but poor quality control and build quality blighted many cars. Another to suffer was the Triumph V8, found in the Stag and also sold in the United States.
Instead of using the famous Rover V8 as its basis, Triumph built its own version of a V8 from scratch. While that itself wasn’t an issue, retaining the placement of the water pump from Triumph’s existing four-cylinder was. With the engine block now tilted to create the V8, the high-sitting water pump became starved of cooling water. Any leaks would cause the pump to go dry, resulting in engine overheating and, ultimately, an engine failure.
Cadillac V8-6-4
Cadillac is a pioneer of the V8 engine, producing them since 1914 and forging a legendary reputation with its eight-cylinder block. However, in the 1980s, Chrysler V8s became big, lumbering engines with low power outputs thanks to the various gas crises of the 1970s and the rise in oil prices.
The V8-6-4 was the nadir of these big, underpowered engines. It was a clever engine, using an array of sensors to monitor the engine, which could then shut down cylinders to help save fuel by turning the engine into a V6 or four-cylinder. Sadly, the 1970s-built computer was too slow to keep up with the engines, and the entire system was prone to failure. Many owners had the system stripped out of their Cadillacs when they came in for a service.
Honda CVCC Four-Cylinder
Many will also be quite surprised to see a Honda engine on this list. The CVCC four-cylinder, however, was not without its faults. The 1751 CC engine, found in the original Honda Accord, would develop a head gasket leak between the third and fourth cylinders every 30,000 miles or so.
A user on Hagerty said that within 60,000 miles of driving his 1977 Honda Civic CVCC, the engine had eaten through three water pumps and blown a head gasket. Following this, the engine never ran correctly, and the CVCC was quite clearly not Honda’s finest hour. It was a rare blip on a near-perfect record, but it is far from the worst engine Honda has ever produced.
Opel 2.2 16v Ecotec
The 2.2 16 Ecotec engine is in the Opel Vectra and Signum, but it is also under the hood of the Chevrolet Malibu and Pontiac G5. One advantage of the X22 versions of the engines is that they come with timing belts and not chains, making them much easier to maintain.
But the Z22 engines cause the most significant problems. The complex timing system can lead to the tensioner wearing out, which is then amplified by the faulty injection system. Other engines would suffer from excessive fuel consumption, and the problem found its way into other North American models, such as the Saturn Vue and Chevrolet Cobalt.
2017 Honda RA617H
Another poor engine from Honda and its time with McLaren in Formula 1. Honda had enjoyed a much more competitive 2016 season, and the 2017 engine in the McLaren MCL32 was the engine to launch the team and engine supplier up the grid.
But it was again another tough season for McLaren-Honda. The cars were slow and unreliable, and pre-season testing saw a near-repeat of the horrible 2015 winter testing that McLaren and Honda went through. McLaren would again finish ninth in the championship, and at the end of the year, McLaren left Honda as the Japanese manufacturer moved to Toro Rosso and then Red Bull. That has, however, worked out quite well.
Alfa Romeo 2.0 TwinSpark 16v
Engine problems in an Alfa Romeo are not uncommon, although some of the stereotypes are perhaps a little unfair. However, the TwinSpark 16-valve powertrain can cause a particular set of problems in the 2.0-liter form.
Out of all TwinSpark engines, these are the most fragile. Oil change intervals need to happen more regularly then Alfa Romeo themselves say. The engines also hate running in cold conditions unless adequately warmed up. Failure to do this can result in the engines breaking down in quick acceleration scenarios, and the timing belt will need replacing every 35,000 miles.
Ford Lima
The Ford Lima is one of the rare occasions that the Blue Oval has gotten quite badly wrong. The biggest issue was that when placed under the hood of the Mustang, they could produce as little as 89 hp.
A muscle car is, of course, meant to be loud, powerful, and brash, so an engine producing just 89 hp is never going to cut it. But sadly, the Lima would find its way into other vehicles, too, such as the Ranger pickup truck, the Aerostar vans, and the Pinto. Near the end of its run, Ford squeezed out 205 hp under the hood of the Mustang SVO.
Mazda 1.3 Renesis
This engine would find its way under the hood of the Mazda RX-8, proving the nadir of what was otherwise a great sports car. That is perhaps unfair, though, because many of the problems with the RX-8 are down to faulty ignition coils, not the actual 1.3 Renesis engine.
When you have an agile sports car with a rotary engine producing 238 hp, then you still have a great baseline. There was the usual high oil consumption that is common with rotary engines. But thanks to the ignition coil problem, Mazda would throw away many perfectly usable Renesis engines. So the Renesis is a lousy engine because of an unfair reputation, not because it could have been better.
