A CLK320 CDI service starts with engine oil and filter work, the checks due for its A or B visit, and additional replacements identified from the service history. Budget separately for overdue brake fluid, air or fuel filters and any gearbox work. This guide covers the 3.0-litre OM642 diesel CLK.
Covered cars: CLK320 CDI C209 coupé and A209 cabriolet, model types 209.320/420, with the 2,987 cc OM642.910 V6 diesel, 165 kW / 224 hp. MANN lists its CLK320 CDI application from May 2005 to October 2009; catalogue dates are not UK registration cut-offs. The petrol CLK320 and earlier CLK270 CDI use different engines.
CLK320 CDI service checklist
| Maintenance item | What to include in your plan |
|---|---|
| Engine oil and oil filter | Check the DPF equipment and oil approval. The inspected CLK manual lists 8.5 litres including a filter change. |
| Engine air filters | Account for both positions: MANN lists C 25 004 left and C 27 006 right for this diesel. |
| Cabin filter | Identify right- or left-hand drive and THERMATIC or THERMOTRONIC equipment before ordering. |
| Diesel fuel filter | Match the actual water-sensor connection; the catalogue has more than one branch. |
| Brake fluid | The inspected 2008 CLK manual specifies renewal every two years. Check the dated invoice or service-book entry. |
| Brakes, tyres and condition checks | Have the workshop identify the inspection scope and record any findings separately from routine replacements. |
| Transmission | Keep the gearbox identity and its service record with the car. Engine servicing does not establish gearbox maintenance. |
This is a planning checklist, not a direction to replace every filter at every visit. Use the car’s service information and previous renewal dates to identify what is due now.
What do Service A and Service B mean on this CLK?
The 2008 CLK handbook calls the system ASSYST and describes A as the smaller service and B as the larger service. It shows reminders in days or distance. That is the appropriate starting point for this generation.
Photograph the complete reminder when booking. Our ASSYST and ASSYST PLUS guide explains the wider terminology. A checklist copied from a later car’s numbered suffix cannot establish this CLK’s work due.
How much does CLK servicing cost in the UK?
Dronsfields in Oldham advertises the following CLK-class packages, checked on 23 October 2026:
| Advertised package | Price including VAT |
|---|---|
| Dronsfields “Option A” | From £342 |
| Dronsfields “Option B” | From £426 |
These are the provider’s advertised CLK starting prices, not quotes obtained for an individual CLK320 CDI. The price page says age/mileage items can add to the total and AMG Line prices may vary. Confirm the diesel’s included work and current price before booking.
To compare a dealer and an independent, request the same list of operations and ask for the oil product, quantity, filter references, labour and VAT. If one quote includes both air filters, brake-fluid renewal or overdue fuel-filter work, compare that total with a matching package rather than a basic headline price.
Buying oil and filters for the diesel
Our CLK320 CDI oil-capacity and approval guide explains the 8.5-litre figure, DPF distinction and a named oil buying option. The CLK320 CDI filter guide covers the left/right air elements, RHD cabin options and fuel-filter connections.
The petrol CLK320’s parts are different. For example, MANN lists HU 718/5 x for the M112 petrol application and HU 821 x for this OM642 diesel. Keep “CDI” and the engine identity in a parts enquiry.
What can an owner do?
Start with tyre pressures, fluid-level checks permitted by the handbook, the service reminder and a review of invoices. An experienced owner can assess oil/filter or accessible cabin-filter work using the exact procedure, tools and safe working arrangements. Record the date, mileage, oil specification and part references.
For workshop work, ask for a completed checklist and an invoice distinguishing scheduled maintenance, condition-led repairs and optional extras. Report starting problems, warning lights or oil leaks when booking so diagnosis can be quoted separately.
A useful check for a stored or lightly used CLK
The CLK handbook says ASSYST does not count time while the battery is disconnected. Note the service due date before storage, or give the workshop the disconnected periods. A low annual mileage does not remove time-dependent maintenance.
After servicing, retain the completed records as well as the new countdown. If buying the car, ask specifically for brake-fluid and transmission invoices; a dashboard reminder cannot tell you which operations were carried out.
Find other models in the Mercedes maintenance hub. For fault-reading equipment, use our Mercedes diagnostic scanner guides and check exact vehicle and function coverage.
Sources
- Mercedes-Benz Public Archive: CLK320 CDI cabriolet and Hengst manufacturer’s CLK applications — engine and model identification.
- Mercedes 2008 CLK manual, printed pages 206–207 — ASSYST A/B and disconnected-battery time; printed page 341 — brake-fluid renewal; printed page 339 — oil quantity.
- MANN 2024–26 catalogue, printed pages 212–213 / PDF 268–269 — engine, cabin and fuel-filter branches.
- Dronsfields service prices — dated UK CLK package examples.
Checked 23 October 2026. The 2008 Mercedes manual cited here is a German-market edition reproduced by ManualsLib. Use the handbook and service booklet supplied with your car for its equipment and maintenance schedule. For corrections, contact Unusual Cars; keep VINs and registration details private.
