Engine Oil Specifications and Maintenance Guide

Smart Fortwo CDI Oil Specs (OM660) | MB 229.51 Capacity, Filter Cross-Reference & Torque Values

Overview of the OM660 Engine

The OM660 is a three-cylinder turbo-diesel engine developed by Mercedes-Benz for the first-generation Smart Fortwo (W450). Produced between 1999 and 2006, it powered diesel variants primarily in Europe. Canada received the Smart Fortwo CDI in 2005–2006, making it one of the few small diesel passenger cars officially sold in North America.

Compact, efficient, and surprisingly solid, the OM660 uses common-rail direct injection, a fixed-geometry turbocharger, and a wet-sump lubrication system with a top-mounted cartridge oil filter. Output is modest—40 kW (54 hp) at 4 200 rpm and 130 Nm (96 lb-ft) at 1 800 rpm—but maintenance precision is critical due to the engine’s small oil volume and turbocharger lubrication sensitivity.

Due to its extremely small oil capacity, this engine is highly sensitive to correct oil specifications and service intervals. Using the wrong oil or exceeding drain intervals can cause premature wear—especially to the turbocharger.

Engine Oil Specifications

Mercedes-Benz originally specified MB 229.5 full-SAPS oil for the OM660, which provides the highest level of wear protection and detergent capability for non-DPF diesel engines. MB 229.3 is also suitable when 229.5 is unavailable. Later-generation specifications such as MB 229.31, MB 229.51, and MB 229.52 are low-SAPS oils formulated for engines equipped with Diesel Particulate Filters (DPF) or three-way catalytic converters. While these low-SAPS formulations are compatible with the OM660, they are not required. Full-SAPS oils generally offer greater anti-wear and detergent reserves, whereas low-SAPS oils reduce ash formation and deposit risk inside oxidation catalysts.

Specification	Description	SAPS Level	Typical Use
MB 229.3	Older-generation full-SAPS synthetic oil with similar detergent and anti-wear properties.	Full	Acceptable if MB 229.5 is unavailable.
MB 229.5	Full-synthetic, long-drain, high-SAPS oil designed for extended intervals and maximum wear protection.	Full	Recommended for all OM660 engines without DPF.
MB 229.51 / 229.52	Low-ash (SAPS) successor to 229.5 Formulated for DPF-equipped engines.	Low	Compatible but not required for OM660.

When factory-approved oils are not available, a high-quality ACEA C3 synthetic oil may be used. ACEA C3 is a mid-SAPS category and represents a balanced alternative between protection and catalyst safety. Many independent formulators produce oils that meet or exceed MB 229.x test requirements but are listed as “recommended for” rather than “approved.” These products often perform at or above OEM standards despite lacking formal certification.

Why Low-SAPS Exists

Higher-ash lubricants can foul oxidation catalysts and form turbocharger deposits, particularly during prolonged high-temperature operation. Low-SAPS oils such as MB 229.31 and MB 229.51 maintain strong anti-wear performance while minimizing residue formation in after-treatment components. However, since the OM660 does not feature a DPF, using a full-SAPS oil like MB 229.5 remains the most protective choice.

Why mid-SAPS?

Higher-ash formulations can foul oxidation catalysts and form turbo deposits. MB 229.31 / 229.51 maintain anti-wear protection while protecting after-treatment components.

Viscosity Grades and Operating Conditions

The correct viscosity grade depends on climate. A 5W-40 synthetic is the most practical year-round choice for most Canadian operating conditions, while 5W-30 offers slightly improved efficiency in moderate climates. In subarctic conditions, 0W-30 or 0W-40 ensures safe cold starting and proper oil circulation.

Ambient Range	Recommended Viscosity	Notes
−30 °C to +35 °C	5W-30	Best balance of flow and efficiency
−20 °C to +45 °C	5W-40	Greater film strength in heat or load
Below −30 °C	0W-30 / 0W-40	Extreme-cold starting (Canadian winters)
Above +40 °C or heavy duty	5W-40	Reduces consumption and shear

For further details on viscosity selection, see the Engine Oil Viscosity Guide page once available.

Oil Capacity and Service Intervals

The OM660’s total oil fill with filter replacement is approximately 3.0 liters (3.17 quarts). Without changing the filter, the refill volume is around 2.8 liters (2.95 quarts). The recommended service interval is every 10,000 km (6,200 miles)or once per year, whichever occurs first.

When refilling, add 2.8 L initially, start the engine briefly, then wait several minutes before topping up to the dipstick’s maximum mark. Overfilling beyond 3.0 L can result in oil carryover into the intake system and potential turbocharger seal failure.

Item	Specification
Oil capacity (with filter)	≈ 3.0 L
Oil capacity (without filter)	≈ 2.8 L
Drain-plug thread	M12 × 1.5 (mm) aluminum crush washer
Standard interval	10 000 km or 1 year (whichever first)
Severe/high-mileage	7 500 km (> 200 000 km or short-trip use)

Drain-Plug and Extraction Methods

Both drain-plug and suction-extraction methods are acceptable on the OM660. Each has advantages:

Drain-plug Method

Access the rear M12 × 1.5 plug to fully evacuate oil and inspect for metal particles. Always install a new aluminum washer and torque to 25 Nm (18 ft-lb). Over-tightening can distort the thin aluminum pan.

Suction Extraction

Insert a ~6 mm tube into the dipstick port to reach the sump pocket. This factory-supported method is fast, clean, and removes ≈ 95 % of used oil. For high-mileage or sludge-risk engines, perform an occasional drain-plug service to confirm sump cleanliness.

Oil Filter Information and Cross-References

The North American market OM660 (Smart Fortwo CDI 2005–2006) uses a bottom-mounted spin-on oil filter, not a cartridge. It threads onto the oil cooler housing beneath the engine. Replace the filter and lightly oil the gasket before installation. Hand-tighten until snug, then turn an additional ¾ rotation (≈ 15 Nm).

Some early European versions of the OM660 used a top-mounted cartridge filter; confirm your setup before ordering.

Common spin-on filter options include:

Manufacturer	Part Number	Notes
MANN-Filter	W 712/92	OEM supplier
Mahle / Knecht	OC 593/4	Direct equivalent
Hengst	H90W03	European aftermarket
WIX	51356 / 51357	North American cross
NAPA	1356	NAPA Gold Oil Filter
Bosch	1 457 429 249	Equivalent design
Purflux	L267D	French OEM cross
AMSOIL	EA15K13	Synthetic-media cartridge compatible with HU 716/2 x

Download: Smart Fortwo OM660 Quick Reference (PDF) – includes specs, capacities, torques, and reset steps.

CSV version: Oil & Torque Quick Reference

Torque Specifications

The oil filter should be installed hand-tight plus three-quarters of a turn (approximately 15 Nm / 11 ft-lb). The oil drain plug should be torqued to 25 Nm (18 ft-lb) using a new crush washer. Undertray fasteners should be tightened between 8–10 Nm (6–7 ft-lb). Always use a torque wrench when possible, as the plastic and aluminum components in the OM660 are easily damaged by over-tightening.

Component	Torque	Notes
Oil drain plug	25 Nm (18 ft-lb)	Replace washer each service
Oil filter (spin-on)	Hand-tight + ¾ turn (≈ 15 Nm)	Lightly oil gasket before install
Undertray bolts	8–10 Nm (6–7 ft-lb)	If removed for access
Oil filler cap	Hand-tight	Avoid tools

Download: Smart Fortwo OM660 Quick Reference (PDF) – includes specs, capacities, torques, and reset steps.

CSV version: Oil & Torque Quick Reference

Maintenance Best Practices

High-mileage engines: Use 5W-40 MB 229.51 and shorten intervals to ≈ 7 500 km. Inspect crankcase ventilation hoses and EGR passages for soot.

Sludge prevention: Achieve full operating temperature regularly; avoid mixing brands or partial fills.

Winter operation: In ≤ −25 °C, favor 0W-30 or 5W-30 MB 229.51 oils; ensure block-heater and glow-plugs function correctly.

Service-Indicator Reset (Wrench Symbol)

Reset the wrench icon after oil service:

Turn ignition to position 1 (do not start).
Within 4 seconds, press the cluster button twice to display the wrench.
Turn ignition off within 10 seconds (the icon stays lit).
Hold the button and switch ignition on.
Continue holding ≈ 10 s until the spanner flashes and resets.

If the indicator doesn’t appear at step 2, try 3–4 taps instead. Minor timing variation exists between early and late W450 clusters.

Common Mistakes & Warnings

Common servicing errors include overfilling the crankcase, reusing crush washers or O-rings, and installing incorrect filter types. Installing a cartridge-style filter on a spin-on housing will result in catastrophic oil loss on startup. Always confirm the filter type before service. Using a low-quality or gasoline-rated oil can accelerate sludge formation and shorten turbocharger life. Skipping regular maintenance intervals may cause soot accumulation and reduced compression over time.

Mistake	Consequence
Overfilling above max	Aeration → turbo seal leakage
Gasoline-only oil	Poor soot handling, wear increase
Reusing crush washer	Persistent seepage
Over-tightening spin-on filter	Damaged gasket, leaks on restart, Can not remove
Ignoring intervals	Soot overload, viscosity rise
Mixing brands/grades	Additive conflict
Removing undertray permanently	Airflow disruption, debris risk

Sources and Verification

Data compiled from Mercedes-Benz WIS/ASRA documentation, European and Canadian OM660 service manuals, and manufacturer cross-reference catalogs (MANN, Mahle, Hengst, WIX). All specifications verified against MB 229.x standards and ACEA C3 criteria

FAQ

Does the Smart Fortwo CDI have a drain plug?

Yes – M12 × 1.5 with crush washer; both drain and suction methods are supported.

What is the correct oil capacity?

≈ 3.0 L with filter (2.8 L without). Fill gradually and recheck after 5 min.

Which oil specification should I use?

A mid-SAPS synthetic meeting MB 229.31 or MB 229.51; 5W-30 or 5W-40 per climate.

Is MB 229.52 compatible?

Yes – it’s backward-compatible and acceptable for the OM660.

How often should oil be changed?

Every 10 000 km or 1 year; 7 500 km for short-trip or high-mileage use.

Cut Through the Oil Talk. Get the Facts.

Updated 26 Oct 2025