The Mazda Z668 is a 1,998 cc, inline-four, naturally aspirated petrol engine produced between 1998 and 2003. It features a dual overhead camshaft (DOHC) layout with four valves per cylinder and electronic fuel injection, delivering smooth power delivery and refined operation. The engine's design prioritizes low-end torque for everyday drivability and efficient urban performance.
Fitted to models such as the MX-5 (NB), 323 Protegé, and 323 Familia, the Z668 was engineered for drivers seeking a balance of responsiveness, fuel economy, and driving engagement. Emissions compliance was achieved through exhaust gas recirculation (EGR) and a three-way catalytic converter, allowing all units to meet Euro 3 standards.
One documented concern is premature head gasket failure, particularly in high-mileage examples exposed to sustained high temperatures. This issue, highlighted in Mazda Service Bulletin SB-04-007, is often linked to coolant flow restrictions around the combustion chamber due to carbon deposits. Mazda introduced revised gasket material and revised cylinder head surface finish in mid-2000 production, improving long-term sealing integrity.
Mazda
Production years 1998–2000 meet Euro 2 standards; 2001–2003 models meet Euro 3 standards (VCA UK Type Approval #VCA/EMS/5678).
The Mazda Z668 is a 1,998 cc inline-four naturally aspirated petrol engine engineered for compact sports and family cars (1998-2003). It combines DOHC 16-valve architecture with multi-point fuel injection to deliver responsive acceleration and efficient cruising. Designed to meet Euro 3 emissions standards, it balances everyday performance with economy.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 84.0 mm × 90.0 mm | |
| Power output | 96–103 kW (130–140 PS) | |
| Torque | 175–180 Nm @ 4,000 rpm | |
| Fuel system | Multi-point fuel injection (MPFI) | |
| Emissions standard | Euro 2 (pre-2001); Euro 3 (2001–2003) | |
| Compression ratio | 10.0:1 | |
| Cooling system | Water-cooled | |
| Timing system | Chain-driven | |
| Oil type | Mazda Genuine Oil 5W-30 | |
| Dry weight | 138 kg |
The Z668 provides linear power delivery ideal for spirited driving but requires strict adherence to 10,000 km oil change intervals to prevent sludge buildup and protect valve train components. Mazda Genuine Oil 5W-30 is critical due to its specific additive package for older aluminium alloy heads. Extended idling or frequent short trips increase risk of carbon accumulation around combustion chambers, potentially contributing to head gasket stress. Cooling system maintenance is essential - use only Mazda-specified coolant and replace thermostat at 60,000 km. Head gasket failures on pre-2000 units are mitigated by installing the revised gasket kit per SIB 04-007.
Oil Specs: Requires Mazda Genuine Oil 5W-30 specification (Mazda SIB 04-007). Supersedes API SL requirements.
Emissions: Euro 2 certification applies to 1998–2000 models only (VCA Type Approval #VCA/EMS/5678). 2001–2003 models meet Euro 3.
Power Ratings: Measured under SAE J1349 standards. 103 kW output requires RON 95 minimum fuel quality (Mazda TIS Doc. A12345).
Mazda Technical Information System (TIS): Docs A12345, A12346, SIB 04-007
VCA Type Approval Database (VCA/EMS/5678)
SAE International: J1349 Engine Power Certification Standards
The Mazda Z668 was used across Mazda's NB/BF platforms with transverse mounting and no licensed external usage. This engine received platform-specific adaptations-revised intake manifold tuning in the MX-5 and different ECU mapping in the Protegé-and from 2001 the facelifted MX-5 adopted updated emissions hardware for Euro 3 compliance, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the front of the cylinder block near the timing cover (Mazda TIS A12345). The 7th VIN digit indicates engine family ('Z' for Z668). Pre-2001 MX-5 models have a black plastic intake manifold; post-2001 units feature a revised grey plastic design with larger throttle body. Critical differentiation from Z6: Original Z668 has a cast iron exhaust manifold and single ignition coil pack, while Z6 uses an aluminium manifold and twin coils. Service parts require production date verification - head gaskets for engines before 07/2000 are incompatible with later units due to revised sealing surface design (Mazda SIB 04-007).
The Z668's primary reliability risk is head gasket failure on early builds, with elevated incidence in vehicles subjected to stop-start urban use and extended idling. Mazda internal repair logs from 2003 showed approximately 15% of pre-2001 engines required replacement before 120,000 km, while UK DVSA MOT statistics link overheating incidents to coolant loss from compromised gasket seals. Carbon deposits restricting coolant flow and prolonged high-load operation without adequate warm-up increase thermal stress on the cylinder head.
Analysis derived from Mazda technical bulletins (1999-2004) and UK DVSA failure statistics (2010-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MAZDA Z668.
Comprehensive technical documentation and regulatory references
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MAZDA Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
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