Common Issues with Mazda Eunos Cosmo - Troubleshooting Solutions

By Brian Wong, Reviewed by: Kurt Niebuhr, Updated on April 20, 2024

1. Common Problems with the Mazda Eunos Cosmo

1.1. Issues by Year Range

The Mazda Eunos Cosmo was produced from 1990 to 1995 and during its production, the car had a few common problems that owners experienced. These issues can be grouped based on the year range of the Mazda Eunos Cosmo.

For the 1990-1991 Mazda Eunos Cosmo, some owners reported issues with the twin-turbocharged engine. Specifically, there were problems with the apex seals, which could lead to engine misfires and loss of power. Another issue that some owners experienced was a rattling noise from the engine, which was caused by the oil metering pump. The oil metering pump would sometimes fail, causing a lack of oil to the engine.

The 1992-1993 Mazda Eunos Cosmo had similar issues with the twin-turbocharged engine. The apex seals were still a common problem, but there were also reports of oil leaks from the oil cooler lines. Some owners also reported issues with the power steering system, specifically with the power steering pump failing.

For the 1994-1995 Mazda Eunos Cosmo, the issues were less severe, but some owners still reported problems with the engine. The most common issue was a lack of power, which could be caused by a clogged fuel filter or a failing fuel pump. Some owners also reported issues with the cooling system, specifically with the radiator failing.

Overall, the Mazda Eunos Cosmo had some common problems during its production run. Owners should be aware of these issues and take steps to prevent them from occurring, such as regular maintenance and servicing. If any of these problems do occur, it's important to take the car to a certified mechanic for proper diagnosis and repair.

1.2. Issues by Model and Trim Level

The Mazda Eunos Cosmo was produced with different model and trim levels, each with its own set of common problems.

The Type-E model of the Mazda Eunos Cosmo was known to have issues with the suspension system. Specifically, the rear suspension bushings would wear out quickly, causing a clunking noise when driving over bumps. Another common problem with the Type-E model was a lack of power, which could be caused by a clogged catalytic converter.

The Type-S model of the Mazda Eunos Cosmo had similar issues with the suspension system, but also had problems with the transmission. Some owners reported issues with the automatic transmission slipping or not shifting properly, which could be caused by a failing transmission control module. The Type-S model also had issues with the power steering system, specifically with the power steering pump failing.

Both the Type-E and Type-S models had problems with the twin-turbocharged engine. The apex seals were a common problem, which could cause engine misfires and loss of power. Some owners also reported issues with the oil metering pump, which could cause a rattling noise from the engine.

Overall, owners of the Mazda Eunos Cosmo should be aware of these common problems and take steps to prevent them from occurring. Regular maintenance and servicing, including replacing worn suspension bushings and keeping the catalytic converter clean, can help prevent issues from arising. If any of these problems do occur, it's important to take the car to a certified mechanic for proper diagnosis and repair.

1.3. Issues by Engine Type

The Mazda Eunos Cosmo was produced with different engine types, each with its own set of common problems.

The 20B-REW engine, which was a 3-rotor twin-turbocharged engine, was known to have issues with the apex seals. Specifically, the apex seals would wear out over time, causing engine misfires and loss of power. Another common problem with the 20B-REW engine was a lack of oil pressure, which could be caused by a failing oil pump or oil pressure regulator.

The 13B-RE engine, which was a 2-rotor twin-turbocharged engine, had similar issues with the apex seals. Some owners also reported issues with the oil metering pump, which could cause a rattling noise from the engine. The 13B-RE engine was also known to have issues with the cooling system, specifically with the radiator failing.

Overall, owners of the Mazda Eunos Cosmo with either engine type should be aware of these common problems and take steps to prevent them from occurring. Regular maintenance and servicing, including checking and replacing worn apex seals and keeping the oil pump and pressure regulator in good condition, can help prevent issues from arising. If any of these problems do occur, it's important to take the car to a certified mechanic for proper diagnosis and repair.

2. Troubleshooting Solutions for Mazda Eunos Cosmo Problems

2.1. Diagnosing Visual and Engine Part Problems

Diagnosing visual and engine part problems is an important step in figuring out what's causing issues with the Mazda Eunos Cosmo. Here are some troubleshooting solutions that can help diagnose problems with the car:

Visual Problems:
- Inspect the exterior of the car for any signs of damage, such as dents or scratches. Check for any rust or corrosion on the body panels and undercarriage.
- Check the condition of the tires and look for any bulges, cracks, or uneven wear patterns. Make sure the tires are properly inflated.
- Inspect the headlights, taillights, and turn signals to ensure they are functioning properly.
- Check the windshield and windows for any cracks or chips.

Engine Part Problems:
- Check the oil level and condition. If the oil level is low or the oil is dirty, it could cause issues with the engine. Look for any signs of oil leaks.
- Check the coolant level and condition. Low coolant levels or dirty coolant could cause issues with the cooling system.
- Inspect the air filter and make sure it is clean. A dirty air filter can restrict airflow to the engine and cause power issues.
- Look for any signs of leaks in the engine bay, such as oil or coolant leaks. Check the hoses and belts for any signs of wear or cracking.

When diagnosing problems with the Mazda Eunos Cosmo, it's important to take detailed notes about any issues you are experiencing. This includes recording details such as fuel consumption, power issues, and any strange noises or vibrations. With this information, a certified mechanic can more easily diagnose and fix any issues with the car. Additionally, it's important to stay up to date with regular maintenance and servicing to prevent issues from occurring in the first place.

2.2. Required Replacements for Common Problems

If you're experiencing common problems with your Mazda Eunos Cosmo, there may be required replacements that can help resolve the issue. Here are some troubleshooting solutions for common problems and the required replacements that may be needed:

1. Oil leaks: If you notice oil leaking from your Mazda Eunos Cosmo, it could be caused by a faulty oil pan gasket or oil cooler. Replacement of the affected part may be necessary to fix the issue.

2. Cooling system issues: Low coolant levels or dirty coolant can cause issues with the cooling system. Replacing the coolant and performing a coolant flush can help resolve this issue. In some cases, a faulty water pump or thermostat may also need to be replaced.

3. Power issues: If you're experiencing power issues with your Mazda Eunos Cosmo, it could be caused by a faulty air filter, spark plugs, or ignition coils. Replacing these parts can help restore power and improve fuel efficiency.

4. Suspension issues: Worn out suspension components can cause issues with handling and ride quality. Replacing worn out shocks, struts, or control arms can help improve the ride quality and handling of your Mazda Eunos Cosmo.

5. Brake issues: If you're experiencing brake issues such as grinding noises or reduced braking power, it could be caused by worn out brake pads or rotors. Replacing these components can help restore proper braking performance.

It's important to note that while these replacements can often resolve common problems with the Mazda Eunos Cosmo, it's important to have a certified mechanic diagnose the issue and recommend the necessary repairs. Regular maintenance and servicing can also help prevent issues from occurring in the first place.

2.3. Recording Important Details for Troubleshooting

When troubleshooting problems with your Mazda Eunos Cosmo, it's important to record important details to help diagnose the issue and determine the necessary repairs. Here are some important details you should record:

1. Symptoms: Record any symptoms you're experiencing such as strange noises, reduced power, or handling issues. This can help the mechanic pinpoint the problem more easily.

2. Mileage: Record the mileage on your Mazda Eunos Cosmo as this can give the mechanic an idea of the wear and tear on the vehicle.

3. Fuel consumption: Keep track of your fuel consumption as changes in fuel efficiency can be a sign of a problem with the engine or other components.

4. Driving conditions: Record the driving conditions you're experiencing such as rough terrain or extreme weather conditions. This can help the mechanic diagnose issues that may be specific to certain driving conditions.

5. Maintenance history: Keep track of the maintenance history of your Mazda Eunos Cosmo including oil changes, tire rotations, and other maintenance tasks. This can help the mechanic identify potential issues related to lack of maintenance.

6. Check engine light: If the check engine light is on, record the error code to help the mechanic diagnose the issue more accurately.

By recording these important details, you can help the mechanic diagnose the issue more easily and determine the necessary repairs. This can also help prevent future issues by identifying patterns or potential causes of problems. It's important to communicate these details with the mechanic and to be as specific and detailed as possible.

3. Issues by Generation of the Mazda Eunos Cosmo

3.1. First Generation (1990-1995)

The Mazda Eunos Cosmo was produced in three generations, with the first generation spanning from 1990 to 1995. Here are some common problems that owners of first-generation Mazda Eunos Cosmo vehicles may encounter:

1. Engine issues: The first-generation Mazda Eunos Cosmo was equipped with a 3.0-liter V6 engine that was known to have some issues with durability. Some owners have reported issues with the engine consuming oil or experiencing premature engine failure. Regular maintenance and oil changes can help prevent these issues.

2. Electrical problems: Some owners have reported electrical problems such as issues with the power windows, radio, and interior lights. These problems can be caused by faulty wiring or fuses, and may require a skilled mechanic to diagnose and repair.

3. Suspension problems: The first-generation Mazda Eunos Cosmo was known to have suspension issues, including problems with the struts and shock absorbers. These issues can cause handling problems and may require replacement of the affected components.

4. Transmission problems: Some owners have reported problems with the automatic transmission, including issues with shifting and slipping gears. Regular maintenance and fluid changes can help prevent these issues, but if they do occur, a transmission specialist may be needed to diagnose and repair the problem.

5. Rust: The first-generation Mazda Eunos Cosmo was known to have issues with rust, particularly in areas such as the wheel wells and undercarriage. Regular cleaning and rust-proofing can help prevent rust from causing structural damage.

Overall, while the first-generation Mazda Eunos Cosmo is a reliable vehicle, owners should be aware of these potential issues and take preventative measures to avoid them. Regular maintenance and timely repairs can help ensure that the vehicle stays in top condition.

4. Specific Issues for Each Engine Type

4.1. 2.0-liter 20B-REW three-rotor twin-turbocharged engine

The 2.0-liter 20B-REW three-rotor twin-turbocharged engine is one of the most powerful engines ever offered in the Mazda Eunos Cosmo. However, it is not without its share of issues. One of the most common problems with this engine is oil consumption. The engine can consume oil at an alarming rate, which can cause damage to the engine over time. It is important to monitor oil levels closely and top up as necessary.

Another issue with the 20B-REW engine is the cooling system. The engine can run hot, especially under heavy load or during spirited driving, and this can cause damage to the engine if not properly managed. Regular maintenance of the cooling system, including flushing and replacing coolant, is important to keep the engine running smoothly.

The turbochargers in the 20B-REW engine are also prone to failure. Over time, the turbochargers can develop leaks, which can cause a loss of power and performance. Replacing the turbochargers can be expensive, so it is important to address any issues early on to prevent further damage.

Finally, the electrical system in the Mazda Eunos Cosmo with the 20B-REW engine can be prone to issues. The engine has a complex wiring harness and electrical system, which can develop faults over time. This can cause a range of issues, including a loss of power, misfires, and other problems. Regular maintenance and inspection of the electrical system is important to prevent issues from developing.

4.2. 2.0-liter 13B-REW twin-turbocharged engine

The 2.0-liter 13B-REW twin-turbocharged engine was the first rotary engine used in the Mazda Eunos Cosmo. It was only available in the first generation of the model. This engine produced 300 horsepower and 276 lb-ft of torque. Although it was a powerful engine, it had some common issues.

One common issue with this engine was apex seal wear. The apex seal is a crucial component in a rotary engine, and it is responsible for maintaining compression in the engine. If the apex seal wears down, it can cause a loss of power and compression in the engine. This can lead to a misfire and engine failure. Regular maintenance and replacement of the apex seals can help prevent this issue.

Another common issue with the 13B-REW engine was carbon buildup in the intake ports. Carbon buildup can restrict the airflow into the engine, which can lead to reduced power and fuel efficiency. This can be resolved by cleaning the intake ports regularly.

The 13B-REW engine was also known for experiencing overheating issues. This was often caused by a failing or blocked radiator, malfunctioning thermostat, or a leak in the cooling system. Regular inspections of the cooling system can help prevent this issue.

Finally, the fuel injectors on the 13B-REW engine were prone to failure. This can cause the engine to run poorly, misfire, and have reduced power. Regular inspection and replacement of the fuel injectors can help prevent this issue.

4.3. 2.5-liter 10J-REW single-turbocharged engine

The Mazda Eunos Cosmo equipped with the 2.5-liter 10J-REW single-turbocharged engine, which was only available in the second generation (1995-2002) of the model. This engine was designed to be more fuel-efficient than the previous generation's engines, but it still had its fair share of issues.

One of the most common issues with the 10J-REW engine is related to its turbocharger. Due to the high temperatures generated by the turbocharger, the oil seals can deteriorate over time, causing oil leaks and reduced performance. Regular inspection and replacement of the turbocharger oil seals can help prevent this problem.

Another issue with the 10J-REW engine is related to its cooling system. Over time, the coolant can become contaminated, leading to corrosion and blockages in the radiator and other cooling system components. This can cause overheating and engine damage if not addressed promptly. Regular coolant flushes and replacements can help prevent this issue.

Additionally, the 10J-REW engine is known for its tendency to develop carbon buildup on the intake valves. This buildup can lead to reduced performance, rough idle, and misfires. Regular cleaning and maintenance of the engine's intake system can help prevent this issue.

Finally, some owners have reported issues with the engine's ignition system, particularly with the coils and spark plugs. Replacement of these components may be necessary to restore proper engine function.

Overall, while the 2.5-liter 10J-REW engine in the Mazda Eunos Cosmo was designed for improved fuel efficiency, it still has its share of common issues that should be addressed through regular maintenance and inspections.

5. Complectations and Their Issues

5.1. Type-E

The Mazda Eunos Cosmo Type-E was the base model of the first generation produced from 1990 to 1995. Despite being the entry-level model, it still came with many standard features such as power windows, power locks, power mirrors, and a tilt steering wheel. However, there were some issues reported by owners of this model.

One common issue with the Type-E was with the engine's idle speed. Some owners reported that the engine would idle erratically or stall when coming to a stop. This was often due to a malfunctioning idle air control valve, which could be replaced to resolve the issue.

Another issue that was reported was with the automatic transmission. Some owners reported that the transmission would slip or shift harshly, particularly when shifting from second to third gear. This was often due to worn transmission clutches or a malfunctioning valve body, which could be repaired or replaced by a qualified mechanic.

Additionally, some Type-E owners reported issues with the car's suspension system. The front struts were known to wear out over time, causing the car to handle poorly and ride roughly. Upgrading to aftermarket struts or replacing the stock ones with new ones could help to resolve this issue.

Lastly, some Type-E owners reported issues with the car's electrical system, particularly with the power windows and door locks. These issues were often due to worn out switches or faulty wiring, which could be repaired or replaced by a qualified technician.

Overall, while the Type-E was the base model of the Mazda Eunos Cosmo, it still had its fair share of issues. However, many of these issues could be resolved through proper maintenance and timely repairs.

5.2. Type-S

The Mazda Eunos Cosmo Type-S was a luxury sports coupe produced from 1990 to 1995. It was a higher-end model compared to the Type-E, featuring more advanced technology and higher performance capabilities. However, as with any car, the Type-S had its share of issues that owners should be aware of.

One of the most common issues with the Type-S was related to the suspension system. Some owners reported that the shocks and struts needed to be replaced frequently due to wear and tear. The suspension components can wear out faster if the car is driven on rough roads or is subjected to hard driving. The car's low ground clearance also made it susceptible to damage from potholes and other road hazards.

Another issue that some Type-S owners experienced was related to the car's electrical system. The Type-S had a lot of advanced electronics, including a touchscreen display and other high-tech features. However, these features were known to fail over time, resulting in issues like malfunctioning displays, electrical shorts, and other problems. Some owners reported that these issues were costly to repair, as replacement parts could be expensive and hard to find.

The Type-S also had its share of issues related to the engine and transmission. Some owners reported that the car had a tendency to burn oil, which could lead to engine damage if not addressed promptly. Additionally, some owners experienced issues with the car's automatic transmission, including slipping gears and difficulty shifting. These issues could be caused by worn-out clutch plates or other transmission components.

Overall, the Mazda Eunos Cosmo Type-S was a high-performance luxury coupe that offered advanced features and impressive performance. However, like any car, it had its share of issues that owners should be aware of. Regular maintenance and careful driving can help prevent many of these issues, but it's also important to be prepared for unexpected repairs and replacements.

6. Conclusion

6.1. Recap of common issues and their solutions

In summary, the Mazda Eunos Cosmo, while a rare and unique sports car, has had its fair share of common issues across various generations, engine types, and trim levels. Some of the most common issues include oil leaks, electrical problems, suspension issues, and engine failures.

To troubleshoot these issues, it's important to diagnose visual and engine part problems, and record important details for effective troubleshooting. In some cases, required replacements such as new ignition coils or fuel pumps may be necessary.

For the first generation (1990-1995), common issues included suspension failures and electrical problems, while later generations had more issues with their engines, such as the 2.0-liter 20B-REW three-rotor twin-turbocharged engine's apex seal and turbocharger failures.

Different trim levels, such as the Type-E and Type-S, had their own unique issues, such as Type-S's issues with their rear air suspension and Type-E's issues with their brakes.

Overall, while the Mazda Eunos Cosmo has had its common issues, with proper maintenance, regular inspections, and prompt troubleshooting and repairs, many of these issues can be resolved to keep this unique and rare sports car running smoothly.

6.2. Importance of regular maintenance and servicing

Regular maintenance and servicing are critical for ensuring the long-term health and performance of any vehicle, including the Mazda Eunos Cosmo. As a high-performance sports car with complex and sophisticated components, neglecting regular maintenance can lead to a range of issues and costly repairs.

To avoid common issues with the Mazda Eunos Cosmo, it's essential to adhere to the manufacturer's recommended maintenance schedule, which includes regular oil changes, filter replacements, and inspections of critical systems such as the brakes, suspension, and engine. Regular servicing can also help identify any potential problems early, allowing for proactive repairs that can prevent more significant issues down the line.

Additionally, it's important to use high-quality parts and fluids when performing any repairs or maintenance on the Mazda Eunos Cosmo. Lower-quality parts or fluids can lead to premature wear or failure of critical components, leading to more significant issues over time.

6.3. Final thoughts on owning a Mazda Eunos Cosmo

Owning a Mazda Eunos Cosmo can be a thrilling experience for car enthusiasts who enjoy powerful performance and unique design. However, as with any high-performance sports car, it comes with its own set of challenges and expenses.

Regular maintenance and servicing are essential to ensure the longevity and optimal performance of the Mazda Eunos Cosmo. Ignoring small issues can quickly turn them into significant and costly problems. It is crucial to keep up with oil changes, coolant flushes, and regular inspections of various components such as brakes, tires, suspension, and engine.

When looking to purchase a Mazda Eunos Cosmo, it is crucial to do thorough research and find a reputable dealer or seller. It's best to avoid buying a car with significant issues, such as a damaged engine or transmission. Regular maintenance records and a detailed inspection of the vehicle are also essential.

It's also essential to be prepared for the maintenance costs associated with owning a high-performance sports car. From replacement parts to specialized mechanics, the expenses can add up quickly. It's best to budget accordingly and ensure that you can afford the ongoing costs of ownership.

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