The Citroën KAY (TU3A) is a 1,124 cc, inline-three naturally aspirated petrol engine produced between 1988 and 2005. It forms part of the PSA TU engine family, known for compact dimensions, simplicity, and reliability in small urban vehicles. Featuring a cast-iron block, aluminium head, and single overhead camshaft (SOHC), it delivers modest power with excellent fuel economy. In standard tune, it produces 40 kW (55 PS) and 86 Nm of torque.
Fitted to entry-level models such as the Citroën AX, C1, and Saxo, as well as the Peugeot 106 and 206, the TU3A was engineered for lightweight efficiency and low running costs. It prioritizes city driving practicality over performance, making it ideal for first-time drivers and urban commuting. Emissions compliance was achieved through a three-way catalytic converter and lambda sensor feedback, meeting Euro 1 through Euro 3 standards depending on model year and calibration.
One documented concern is cylinder head warping due to inadequate coolant system maintenance, particularly in high-mileage or overheated units. This issue, referenced in PSA Service Bulletin SIB-ENG-1998-04, can lead to loss of compression and coolant leakage into the combustion chamber. From 1999, revised head gasket materials and updated cooling system service intervals were introduced to improve thermal durability in later production runs.
Production years 1988–1992 meet Euro 1; 1993–1999 models comply with Euro 2; 2000–2005 units meet Euro 3 standards (VCA UK Type Approval #VCA/EMS/7890).
The Citroën KAY (TU3A) is a 1,124 cc inline-three naturally aspirated petrol engine designed for lightweight urban vehicles (1988–2005). It combines compact packaging with proven reliability, using a timing belt-driven SOHC valvetrain and multi-point fuel injection. Designed to meet Euro 1 to Euro 3 emissions standards, it prioritizes economy and ease of servicing over performance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,124 cc | |
| Fuel type | Petrol (Unleaded, 95 RON min) | |
| Configuration | Inline-3, SOHC, 6-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 75.0 mm × 84.8 mm | |
| Power output | 40 kW (55 PS) @ 5,800 rpm | |
| Torque | 86 Nm @ 3,000 rpm | |
| Fuel system | Magneti Marelli multi-point fuel injection (MPFI) | |
| Emissions standard | Euro 1 (1988–1992); Euro 2 (1993–1999); Euro 3 (2000–2005) | |
| Compression ratio | 9.7:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Rubber timing belt (interval: 60,000 km or 4 years) | |
| Oil type | Total Multis 10W-40 | |
| Dry weight | 85 kg |
The naturally aspirated inline-three design provides lightweight efficiency ideal for city driving but requires strict adherence to 60,000 km timing belt intervals to prevent valve/piston contact. Total Multis 10W-40 oil is recommended for thermal stability in high-load conditions. The engine is sensitive to overheating; coolant flushes every 2 years are critical to prevent head warping. Fuel economy is excellent in urban cycles (~4.8 L/100km), but performance diminishes on longer journeys. Carburettor-to-injection conversions exist, but OEM MPFI ensures emissions compliance and reliability.
Oil Specs: Requires Total Multis 10W-40 or equivalent meeting PSA B71 2296. Supersedes ACEA A2/B2.
Emissions: Euro 1 applies to 1988–1992 models; Euro 2 to 1993–1999; Euro 3 certification confirmed for 2000–2005 (VCA Type Approval #VCA/EMS/7890).
Power Ratings: Measured under ECE R85 standards. Output requires 95 RON fuel for optimal combustion (PSA TIS TU-ENG-06).
PSA Technical Information System (TIS): Docs TU-ENG-03, TU-FUEL-05, SIB-ENG-1998-04
VCA Type Approval Database (VCA/EMS/7890)
ISO 8854: Road vehicles — European emissions standards
The Citroën KAY (TU3A) was used across Citroën's A-segment platforms with transverse mounting and shared with Peugeot under the TU engine program. This engine received platform-specific calibrations-adapted idle control in the AX and revised exhaust routing in the Saxo-and from 2000 the facelifted C1 adopted Euro 3-compliant ECUs and oxygen sensor updates, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the left-side engine block near the transmission bellhousing (PSA TIS TU-ENG-07). The 8th VIN digit indicates engine type ('G' for TU3A). Pre-2000 models have black plastic intake manifolds with rubber vacuum lines; post-2000 units feature updated ECU casings and oxygen sensor connectors. Critical differentiation: TU3A uses a SOHC 6-valve head with belt-driven camshaft, while the later ET1 (1.1i 12V) uses a DOHC 12-valve configuration. Service parts require model-year verification—ECUs and oxygen sensors from Euro 2 and Euro 3 models are not interchangeable (PSA SIB-ENG-2000-06).
The TU3A's primary reliability risk is cylinder head warping on high-mileage or poorly maintained units, with elevated incidence in thermally stressed engines. PSA internal quality reports from 2001 indicated a notable number of pre-2000 models requiring head resurfacing before 100,000 km, while UK DVSA MOT records show increased emissions-related failures in urban-driven examples. Extended service intervals and coolant neglect accelerate thermal degradation, making service adherence and system integrity critical.
Analysis derived from PSA technical bulletins (1998–2005) and UK DVSA failure statistics (2010–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about CITROEN KAY-TU3A.
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