The Smart Roadster oil cooler on the 60kW is one of the most consequential differences between the standard engine and the entry-level 45kW Lite — yet it rarely appears in buying guides and is almost never discussed by sellers. If you are choosing between variants, already own a 45kW, or are considering remapping either engine, understanding exactly what this component does, why Smart and Mitsubishi fitted it to the 60kW from the factory, and what happens when it is absent or fails, could save your engine. This article covers the engineering rationale, the thermal limits of the 698cc three-cylinder, how the cooler interacts with boost and oil viscosity, and the implications for owners who want more power.
What the Oil Cooler Actually Does on the 698cc Engine
The Smart Roadster’s 698cc three-cylinder turbocharged engine is a compact, highly stressed unit derived from Mitsubishi’s M160 architecture. Because it is mid-rear mounted in an extremely tight engine bay with limited airflow, thermal management is a genuine engineering challenge rather than an afterthought. Oil in this application does far more than lubricate: it cools the piston crowns from below, manages turbocharger bearing temperatures, and regulates the thermal load on the crankshaft and rod bearings.
The oil cooler on the 60kW variant is a small plate-type heat exchanger mounted in the engine oil circuit. Coolant from the main water circuit passes through the cooler, absorbing heat from the engine oil before it returns to the sump. This keeps oil temperature in a safe operating band — typically below 120°C — preventing viscosity breakdown. When engine oil overheats, its film strength collapses, and bearing surfaces begin to make metal-to-metal contact. In a turbo engine that sees sustained boost, this degradation can happen surprisingly quickly.
The 60kW runs 1.09 bar of boost against the 45kW’s 0.89 bar. That extra pressure translates directly into more combustion heat, more exhaust energy through the turbocharger, and higher thermal load on the oil. Smart’s engineers recognised that without active oil cooling at this power level, oil temperatures would regularly exceed safe limits during spirited driving or in warm climates.
Why the 45kW Lite Was Built Without an Oil Cooler
The 45kW Lite was a deliberate cost-reduction exercise. Smart needed a lower entry price to make the Roadster accessible, and stripping out the oil cooler — along with a detuned ECU map and lower boost — was part of that package. At 0.89 bar of boost and 45kW peak output, the thermal load on the oil is meaningfully lower, and in normal road use the engineers judged the risk acceptable.
The problem is that this judgement assumed stock boost, a healthy cooling system, and modest driving cycles. In practice, 45kW cars frequently develop coolant leaks, are driven hard by enthusiastic owners, and — critically — are sometimes remapped without the oil cooler being retrofitted first. Even at stock tune, a 45kW Roadster driven on a warm track day or a long Continental motorway run in summer can put its oil under serious stress. The absence of an oil cooler is the single biggest reason why we advise against the 45kW as a long-term keeper or a tuning platform. You can read more about the mechanical differences between these two engines in our detailed breakdown of every Smart Roadster variant, which covers specification differences that matter at the point of purchase.
It is also worth noting that the 45kW omits the oil cooler even though the block and head are essentially the same castings. The oil cooler is not impossible to add retrospectively — the ports and threads exist on the block — but it requires sourcing the correct 60kW cooler assembly and associated plumbing, and verifying the coolant circuit can accommodate it.
The Oil Cooler’s Role When You Remap or Raise Boost
Anyone remapping a Smart Roadster needs to treat the oil cooler as a non-negotiable prerequisite, not an optional upgrade. When boost climbs — whether to the 66kW SB2’s 1.33 bar or toward the Brabus’s 1.43 bar — the heat rejection demands on the oil increase substantially. The turbocharger bearings in particular depend on cool, clean oil; the Garrett 1238S is a small unit that spins at very high rpm, and its centre bearing section is particularly sensitive to oil coking caused by hot shutdown after spirited running.
On a remapped 60kW with a functioning oil cooler, oil temperatures under boost remain manageable. On a 45kW without one, even a modest remap pushing boost above 1.0 bar introduces genuine risk of oil degradation within a single hard driving session. If you are curious how boost levels differ across the variant range and what the ECU is actually doing to achieve them, our article on boost map differences between all four Smart Roadster variants explains the ECU logic and pressure targets in detail.
If you do want to convert a 45kW car and fit the oil cooler as part of that process, the conversion is technically feasible but involves more than just bolting on the cooler — the ECU, boost control, and fuelling all need to change simultaneously. Our guide on whether a 45kW to 60kW conversion is worthwhile walks through the full scope of that project honestly.
Identifying and Inspecting the Oil Cooler
On a 60kW Roadster, the oil cooler is located on the rear of the engine, accessible from the back of the car with the engine cover removed. It is a compact aluminium plate-type unit with two coolant hose connections and an oil circuit that integrates with the main gallery. When inspecting a used car, look for:
- Coolant contamination in the oil — a mayonnaise-like emulsion under the oil filler cap or on the dipstick is a red flag, though this is more often a head gasket symptom
- Oil in the coolant — a brownish film or oily residue in the expansion tank can indicate a cooler that is passing oil into the coolant circuit
- External seepage — check for oily staining around the cooler body and hose connections
- Brittle or cracked hoses — the cooler hoses are small-diameter and can harden and split with age, causing coolant loss
A cooler that is leaking internally — allowing oil and coolant to mix — is not immediately catastrophic but must be replaced promptly. Diluted oil loses its lubricating properties rapidly. Replacement coolers are available from Smart specialists and some Mitsubishi Colt parts suppliers, as the M160 engine family shares components across markets.
While you have the engine cover off for inspection, it is also worth checking the boost system components. The wastegate actuator, for instance, directly governs how much thermal load the engine sees under boost — a sticky or leaking actuator can cause overboosting that accelerates oil degradation. See our guide on diagnosing and replacing the wastegate actuator for what to look for.
Oil Choice and Service Intervals on the 60kW
Even with a fully functioning oil cooler, oil selection and service intervals matter enormously on this engine. Smart’s official specification calls for a low-viscosity fully synthetic oil — 0W-40 or 5W-40 is commonly recommended — that maintains film strength at elevated temperatures. The small sump capacity (around 2.5 litres with filter) means that any degradation in oil quality affects the entire charge quickly.
Service intervals of 10,000 miles or annually are the official figure, but most experienced Roadster owners and specialists recommend 6,000 miles or every six months for cars used enthusiastically. A turbocharged engine with a small sump and high specific output has no margin for extended oil life, regardless of what the service book says. Using a quality oil analyser service annually will tell you far more about your engine’s health than any visual inspection.
For tuned cars — whether running our BASIC 90 HP, PLUS 100 HP, PRO 110 HP, or EVOLUTION 125 HP maps — we recommend reducing service intervals further to 5,000 miles. The oil cooler remains effective at these power levels on the 60kW platform, but the oil itself is working harder and should be renewed more frequently. If you are interested in what our remap packages offer and how they interact with the engine’s thermal limits, our performance mapping packages page details each stage and the hardware prerequisites we require before flashing a tune.
The Broader Lesson for Smart Roadster Buyers
The oil cooler story encapsulates something important about the Smart Roadster: it is an engineering-led car where small specification differences have large real-world consequences. The 45kW was not built to a worse standard — it was built to a different duty cycle. The problem is that most buyers and many enthusiasts do not know the difference until something goes wrong.
When evaluating any Smart Roadster for purchase, knowing the exact variant is essential. The VIN decodes the engine variant, and any honest seller should be able to confirm whether the car is a 45kW Lite, 60kW standard, 66kW SB2, or full 74kW Brabus. Do not rely on the badge alone; the Roadster Coupe and Roadster-Coupé Brabus badges were sometimes applied to non-Brabus cars by previous owners. Once you have confirmed the variant, the presence and condition of the oil cooler should be on your inspection checklist for every 60kW, 66kW, and 74kW example you consider.
External References
For readers who want to understand the engineering principles behind oil cooling in turbocharged engines, Engine Builder Magazine’s technical overview of engine oil coolers explains heat exchanger design and integration in detail. The role of oil viscosity breakdown at elevated temperatures is documented thoroughly in Total Lubricants’ technical guide to oil degradation. For the Garrett 1238S turbocharger itself, Garrett Motion’s engineering content on turbocharger oil cooling provides manufacturer-level insight into why turbo bearing lubrication is so sensitive to oil temperature.
The Smart Roadster oil cooler on the 60kW is not a luxury feature — it is the difference between an engine that will last 150,000 miles with proper care and one that is genuinely at risk during any sustained hard use. Whether you are buying, remapping, or simply maintaining your Roadster, treat the oil cooler as a critical system, inspect it at every service, and never allow a 45kW car to be tuned without retrofitting one first. Get this right, and the 698cc three-cylinder is a surprisingly durable unit. Get it wrong, and the repair bill will be substantial.
