Mercedes-Benz SLK-Class (R170: 1996-2004)

Corrosion (water-based paint)

In my opinion, rust is by far the number one problem with this car and other Mercedes-Benz vehicles produced between 1993 and 2004. In 1993, Mercedes-Benz implemented a more environmentally friendly, water-based paint.

Unfortunately, the new paint offered less protection from rust. With no galvanizing process, and coupled with steel that wasn’t very corrosion resistant, the R170 SLK-Class is susceptible to corrosion. When buying a Mercedes-Benz from that era, inspecting it for rust should be one of your top priorities.

Mercedes-Benz eventually started galvanizing their cars but it wasn’t until 2004. The production of the R170 stopped in 2004. Only its successor – the Mercedes-Benz R171 received a galvanized body, which is significantly more corrosion resistant.

Complex hardtop roof

The hardtop roof on the R170 is actually pretty good. Few companies succeeded in making a reliable hardtop convertible that doesn’t leak and isn’t as complicated as an open heart surgery.

The hardtop “Vario” roof is operated by five hydraulic actuators, powered by a hydraulic pump. Your two biggest concerns are hydraulic system issues (mainly leaks) and weather intrusion (fancy name for a leaking roof).

Things to check regarding the Vario roof:

• Check for any dampness in the footwells and carpets. Also, check in the trunk underneath the spare wheel. It’s best to do it after rainfall.

• Open and close the roof a couple times to make sure that it works. The roof should take approximately 25 seconds to open or close. If it takes much longer than that, the pump may be on its way out.

• Check the condition of the roof seals. Ideally, they should be lubricated regularly – ask the previous owner about it.

• Check if the level of hydraulic fluid is correct. If it isn’t, then the car may have been neglected or there is a leak somewhere.

• Look for hydraulic fluid leaks – in the boot, on the headliner and around the hydraulic rams.

• Get the car up to 60 mph with the roof closed and listen for excessive wind noise.

• Listen for rattling noises while driving with the roof closed.

• Take the car to a high pressure (touchless) car wash and see if any water gets inside the cabin or the boot.

• Accident-free history is very important for any hardtop convertible. If the car participated in a large crash, the roof may be out of alignment, which can be a nightmare to waterproof if the chassis of the car isn’t “straight” anymore.

The hydraulic rams last only so long before the seals deteriorate and start leaking (15 years reliably at most as I see it). The roof lock cylinder is usually the first one to fail. When it does, the headliner may get soaked in hydraulic oil.

The OEM rams are expensive but there are companies that sell reconditioned units. Also, you can buy just the seals and replace them yourself (advanced DIY).

Along with the hydraulic system, there is plenty of electronics to manage the roof on the R170. These cars are getting quite old and sometimes the roof can be a bit fussy. The roof seals, unless replaced at some point, might be quite tired too so the roof may let some water in when it rains (adjustment and lubrication help).

M111 engine – head gasket failure

The head gasket is the weak point of these engines. Considering head gasket replacement is inevitable at some point, often around 150,000 miles.

Before the gasket fails completely, these engines often develop an external oil leak from the head gasket at the back of the engine. Make sure to inspect that area when buying one of these cars.

Once the head gasket fails and is replaced, the new one should be good for another 100k – 150k miles. This issue mainly affects the inline-6 engines, like the M103 or M104, because of their long cylinder heads. However, the 4-cylinder M111 engines are also affected, but to a smaller degree.

M111 engine – “Kompressor” lifespan

The “Kompressor” variant is fitted with an Eaton (M62 or M45) supercharger. They are reliable but have a finite lifespan. I estimate that they will need to be rebuilt after around 150,000 miles. The engine and other components under the bonnet will last a lot longer, so it’s very likely that the car will need to have the supercharger rebuilt or replaced at some point during its lifetime.

Summary of problems & additional information

• Except for the rust, which can be a serious issue, the R170 should be pretty reliable. Just like the older Mercedes-Benz cars, it is well engineered and relatively easy to work on. It is based on the W202 C-Class chassis, which is quite reliable except for the same poor corrosion resistance.

• Unless you can find a rust free example, I would stay away from this model. If you do decide to buy it, be prepared to spend some time and money on dealing with the rust in the long run. That is if you live in a wet or cold climate. If you live in a place like Spain, buying an R170 is not a bad idea at all.

• If you’re not into DIY and you’re not willing to understand how the roof mechanism operates, don’t get an older hardtop convertible like the R170. It may be reliable, but the roof is a complex piece of machinery and many small things may at some point require fixing (like one of the roof microswitches) or adjusting (like the roof catches). If you can’t diagnose or repair these small things yourself, trying to get the roof sorted out at a car repair shop can get expensive quickly.

• The V6 M112 engine (SLK 320 & SLK 32 AMG) – Mercedes-Benz got this one right. This engine is closely related to the V8 M113 and both are reliable units.

• Watch out for potential head gasket problems in the M111 engines. Also, these engines are supercharged. The superchargers (“kompressors”) have a finite lifespan and they will need to be rebuilt at some point.

• All R170 engines are fitted with timing chains, which normally don’t have a specified replacement interval. The timing chains in the R170 are generally reliable, but they will not last forever. Read more about timing chains.

• If you like the R170 chassis and the V6 M112 engine, have a look at the Chrysler Crossfire. It’s a soft top convertible based on the R170. The Crossfire has better corrosion resistance than the R170.

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