Smart roadster turbo replacement involves draining the oil, removing the rear undertray and heat shielding, disconnecting the oil feed and return lines, unbolting the exhaust manifold flange and compressor outlet, then fitting a new or reconditioned Garrett 1238S with fresh copper crush washers and a pre-oiled centre section. Budget four to six hours for a first attempt.
The Garrett 1238S is a compact but hard-working unit that spins at up to 200,000 rpm on the 60 kW and Brabus variants. When it eventually fails — through oil starvation, contamination or simple age — the consequences range from an oily inlet tract to catastrophic bearing collapse and engine damage. This guide walks you through the complete replacement process: access, ancillary disconnection, removal, inspection of surrounding components, correct installation, and the critical post-fit run-in procedure. Whether you are replacing a seized unit or carrying out a precautionary swap on a high-mileage car, getting the procedure right first time will save you repeating the job.
Understanding the Smart Roadster Turbo Layout Before You Start
The Smart Roadster 452 is a mid-rear engined car. The 698 cc three-cylinder turbocharged engine sits behind the seats, driving the rear wheels. There is no engine at the front — that compartment is purely luggage space. This layout is worth stating clearly because it defines your entire access strategy: all turbo work is done from underneath and behind the car, not from a conventional front-mounted engine bay.
The Garrett 1238S sits on the exhaust side of the engine, tucked between the block and the rear firewall. It receives pressurised oil from the engine’s main gallery via a banjo bolt feed line, and returns oil to the sump via a larger-bore drain hose. Boost pressure is regulated by a pneumatic wastegate actuator mounted on the turbine housing. Understanding how the Garrett 1238S operates at its real aerodynamic limits is useful background before you pull the unit apart, because it tells you what to inspect once the turbo is on the bench.
The 45 kW Lite variant was not fitted with an oil cooler and runs hotter oil; if you own a Lite, this is an additional reason to be meticulous about oil feed line condition. On all variants, check the oil feed banjo filter screen for blockage — a clogged screen is a leading cause of premature turbo bearing failure and the same fault will kill a new unit.
Tools, Parts and Consumables You Will Need
Gather everything before the car goes in the air. A mid-job parts run is avoidable with proper preparation.
Essential tools
- Trolley jack and axle stands rated to at least 1 tonne — never rely on a jack alone
- 10 mm, 12 mm, 13 mm sockets (standard and deep), 3/8 in drive recommended for confined spaces
- E10 external Torx socket for exhaust manifold studs on some builds
- 8 mm and 10 mm combination spanners for banjo fittings
- Breaker bar — exhaust flange nuts will be heat-seized
- Penetrating oil (apply the night before if possible)
- Torque wrench, 10–80 Nm range
- Wire brush and emery cloth for flange faces
- Disposable nitrile gloves, rags, drain pan
Parts and consumables
- Replacement Garrett 1238S turbocharger (new or quality reconditioned)
- Oil feed banjo bolt copper crush washers — always renew these, one either side of the banjo
- Oil return hose (renew if cracked or oil-soaked)
- Exhaust downpipe gasket and turbo-to-manifold gasket
- New M8 exhaust flange nuts (self-locking, high-temperature rated)
- Fresh engine oil — you will drain and refill as part of the job
- High-temperature anti-seize compound for exhaust studs
- Silicone hose joiner or OEM compressor outlet hose if the original is perished
Smart Roadster Turbo Replacement: Step-by-Step Removal
Step 1 — Prepare the car
Run the engine to warm temperature, then allow it to cool for at least 45 minutes. Coolant and exhaust components must be cold to handle safely. Disconnect the negative battery terminal. Raise the rear of the car on axle stands; the front may remain on the ground. Remove the rear undertray — typically six to eight 10 mm bolts. Set a drain pan under the sump and drain the engine oil completely. A contaminated oil supply is usually what killed the original turbo; old oil should not be recycled through the new unit.
Step 2 — Remove heat shielding
The turbo is surrounded by thin pressed-steel heat shields retained by 8 mm bolts. These are fragile and easily distorted; remove them carefully and note their orientation for reassembly. Access to the oil feed banjo and exhaust flange is impossible without removing them first. Some bolts will be corroded — apply penetrating oil and use a correctly fitting socket rather than a ring spanner to avoid rounding heads.
Step 3 — Disconnect the compressor side
Loosen the jubilee clips or spring clamps securing the compressor inlet hose (from the airbox) and the compressor outlet hose (to the intercooler). Pull both clear. Plug the intercooler pipe opening with a clean rag to prevent debris ingress. If the outlet hose is cracked or has collapsed internally, this is the moment to replace it — our guide to intercooler pipes, boost leaks and silicone hose upgrades covers the options in detail.
Step 4 — Disconnect the oil feed line
The oil feed is a small-bore steel-braided or hard line terminating in a banjo bolt on top of the turbo centre section. Place a rag beneath it. Undo the banjo bolt with a 12 mm spanner — two copper washers will fall out; discard them, as they must not be reused. Note the orientation of the banjo fitting. Keep the line clean and capped.
Step 5 — Disconnect the oil return hose
The oil drain hose is larger (typically 18–22 mm internal diameter) and runs downward from the bottom of the centre section to the sump. It is secured by a hose clip or banjo at the turbo end and a clip or flange at the sump. Residual oil will drain — have your pan ready. Inspect the hose for cracks, kinking or internal collapse, all of which restrict drain flow and starve the turbo of return capacity.
Step 6 — Remove the wastegate actuator rod
Disconnect the pneumatic hose from the wastegate actuator. Undo the split-pin and clevis pin connecting the actuator rod to the wastegate lever. If the actuator itself is suspect — perhaps it was already flagged as a fault — this is a logical time to address it; our dedicated article on diagnosing and replacing the wastegate actuator covers the testing procedure and correct rod length setting.
Step 7 — Unbolt the exhaust flange
Three or four M8 nuts secure the turbine outlet to the downpipe. These will almost certainly be heat-seized. Apply penetrating oil the previous day and use a breaker bar with a 13 mm six-point socket. If studs shear — a real risk — they must be extracted before fitting the new turbo. Work methodically, breaking each nut free a little at a time rather than forcing any single one. Once the flange nuts are off, push the downpipe clear; the gasket will likely disintegrate.
Step 8 — Unbolt the turbo from the exhaust manifold
Three or four nuts secure the turbine inlet flange to the exhaust manifold. The same cautions about heat-seized fasteners apply. Once these are free, the turbo can be manoeuvred out from beneath the car. It is heavier than it looks — roughly 3–4 kg — and awkwardly positioned. Have an assistant guide it clear if possible.
Inspection: What to Check While the Turbo Is Out
With the turbo removed, take fifteen minutes to inspect the surrounding components. Check the exhaust manifold face for cracks and warping — a straight-edge reveals any distortion that would cause a boost leak post-assembly. Clean both flange faces with a wire brush and emery cloth. Inspect the oil feed banjo filter screen (a small mesh insert at the feed port on the engine oil gallery side) and clean or replace it if blocked.
On the bench, spin the old turbo’s shaft by hand. Excessive radial play (side-to-side) greater than about 0.5 mm indicates failed journal bearings. Axial play (in and out along the shaft axis) beyond 0.1 mm indicates thrust bearing wear. Look inside the compressor and turbine housings for blade contact marks against the housing walls — this confirms the bearings failed, and you should check the oil system thoroughly before the new unit goes in.
High exhaust gas temperatures accelerate turbine blade and bearing wear significantly. If the previous owner was running an aggressive remap without monitoring EGT, that context matters for understanding why the turbo failed — our explainer on exhaust gas temperature as a hidden threat to tuned three-cylinders is worth reading before you button everything back up.
Smart Roadster Turbo Replacement: Correct Installation
Step 1 — Pre-oil the new turbo
This is the single most important step and the one most often skipped. Before fitting, pour approximately 30 ml of fresh engine oil into the oil feed port on the new turbo’s centre section and rotate the shaft by hand to distribute it across the bearings. Fitting a dry turbo and immediately starting the engine will damage or destroy the new bearings in seconds.
Step 2 — Fit turbo to exhaust manifold
Fit a new manifold-to-turbo gasket. Offer the turbo up, start the nuts by hand and torque evenly in a cross pattern to approximately 22–25 Nm. Apply a small amount of high-temperature anti-seize to the stud threads beforehand — future-you will be grateful.
Step 3 — Connect the oil return hose
Fit the oil drain hose before the feed, because access is better with the feed line out of the way. Secure with new clips and ensure the hose has a continuous downward slope — any upward bend will trap oil and cause centre section flooding.
Step 4 — Connect the oil feed banjo
Fit two new copper crush washers either side of the banjo fitting. Torque the banjo bolt to 17–20 Nm — tight enough to seal, not so tight as to crack the banjo. Do not reuse old washers; they no longer deform correctly and will weep oil.
Step 5 — Connect the exhaust downpipe
Fit a new downpipe gasket. Start the flange nuts by hand, then torque to 22 Nm in sequence. Reconnect any oxygen sensor wiring disturbed during removal.
Step 6 — Reconnect compressor hoses and wastegate
Reconnect the compressor inlet and outlet hoses, tightening all clips securely. Reconnect the wastegate actuator rod and pneumatic hose. Refit the heat shields, ensuring none fowl the turbine housing.
Step 7 — Fill with fresh oil and perform the start-up procedure
Fill with the correct specification engine oil to the upper mark. Do not start the engine immediately. Instead, crank the engine with the fuel pump relay removed for 10–15 seconds to build oil pressure through the feed line before the turbo spins. Refit the relay, start the engine, and idle for a minimum of five minutes without revving. Check for oil or exhaust leaks at all disturbed joints with the engine running. After the five-minute idle, shut down and recheck the oil level; top up if necessary.
Post-Replacement: Running-In and What to Monitor
For the first 500 miles after a smart roadster turbo replacement, avoid sustained high-boost driving. Keep engine speed below 4,000 rpm and avoid wide-open throttle for more than a few seconds at a time. This allows the new bearing surfaces to bed in under controlled conditions. Change the engine oil again at 500 miles — the first oil fill will pick up metallic particles from the new bearings and should not remain in the engine.
Monitor for: blue smoke on start-up (oil getting past seals — may normalise, but persistent smoke indicates a sealing fault), loss of boost pressure, unusual whine or rumble from the turbo, and oil weeping from the feed banjo or drain hose joints. If you see white smoke that was not present before, check the intercooler and outlet hoses for oil pooling — a sign the old turbo had been leaking for some time and the intercooler needs flushing.
It is also sensible to reset any stored fault codes and verify the engine management system is not commanding overboost or running a corrupted fuel map. If the car has a non-standard ECU map, have it checked by someone who understands the Bosch MEG 1.1 platform. Similarly, if the car has been sitting for an extended period or you have concerns about the condition of the air intake side, a quick check of whether the air filter needs attention is worthwhile before putting the car back into full use.
Finally, if the car was exhibiting any start-related symptoms before the turbo failed — hesitation, rough running, refusal to fire — address those independently. A failing turbo can mask other faults, and a fresh unit on a car with underlying fuelling or sensor problems will not perform correctly.
Common Mistakes and How to Avoid Them
- Reusing copper crush washers — they harden and will not seal. Always fit new ones.
- Not pre-oiling the new turbo — dry start is the leading cause of immediate new-turbo failure.
- Fitting with old, contaminated oil still in the engine — always do a full oil change as part of the job.
- Not checking the oil feed banjo screen — if it was blocked, it will kill the new unit too.
- Ignoring the oil return hose — a kinked or deteriorated return hose causes oil to back up in the centre section and blow past seals.
- Over-torquing the banjo bolt — cracked banjos create an immediate pressurised oil leak onto hot exhaust components.
- Skipping the no-fuel cranking step — five seconds of bearing spin without oil supply causes irreversible damage.
Frequently Asked Questions
How much does a Smart Roadster turbo replacement cost?
A quality reconditioned Garrett 1238S typically costs £180–£350; a new unit is £350–£600. Add gaskets, oil, crush washers and consumables for another £30–£60. DIY total is roughly £220–£660. A specialist garage will charge three to five hours of labour on top, typically £400–£750 all-in.
How do I know if my Smart Roadster turbo has failed?
Key signs include blue or grey smoke from the exhaust, oil in the intercooler or inlet tract, a distinct whine or rumble from the turbo at speed, loss of boost pressure, or the engine management light with a boost-related fault code. Shaft play beyond acceptable limits on the bench confirms bearing failure definitively.
Can I use any Garrett turbo as a replacement, or must it be the 1238S?
The Garrett 1238S is the correct unit for the Smart Roadster 452. Its compressor and turbine wheel sizing is matched to the 698 cc engine’s flow requirements and the ECU’s boost targets. Alternative turbos require modification to housings, oil feed orientations and potentially ECU recalibration — not a straightforward swap.
How long does a Smart Roadster turbo last?
With clean oil, correct oil change intervals (every 6,000 miles or annually), and no oil starvation events, a Garrett 1238S can last 80,000–120,000 miles. High-boost remaps, infrequent oil changes and short runs that never fully warm the oil dramatically shorten service life. Pre-oiling on every fit is essential.
