Like many car enthusiasts, the allure of a beautiful machine can be irresistible. For me, that machine was a 1999 Mercedes Sl 500 I found at my Uncle Dave’s shop in New Hampshire. Visiting family, I wasn’t actively car shopping, but seeing this SL 500, despite needing some work, sparked an immediate desire. It was a year older than me and had clocked 121,000 miles, but I was confident. My thinking was simple: acquire the car first, and tackle any issues as they arose. Armed with my savings, I purchased the Mercedes and began the long drive back home to Virginia.
My journey wasn’t without its early trials. Stopping in Massachusetts to see more family, the hydraulic system for the convertible top decided to announce itself. Fluid began spraying from the pistons that controlled the top locks. Luckily, paper towels were on hand to clean up the mess – a fortunate escape, as none of the car’s numerous leaks ever stained the carpet.
Leaving Massachusetts, a new issue emerged: the engine started misfiring. At the time, I didn’t fully grasp the implications. This particular model of the SL 500, part of the R129 generation, boasts a robust V8 engine with 16 spark plugs across its eight cylinders. This meant even with a faulty plug, the engine could still run, masking the underlying problem. Back home in Virginia, curiosity led me to open the hood and investigate.
I sold the car but I miss it. I learned a lot of skills and a lot about cars. I went into this knowing nothing to now knowing most of what you could know.
To understand the “check engine” light and the misfiring, I took the SL 500 to a local repair shop. This experience quickly highlighted a crucial lesson: shops accustomed to modern daily drivers aren’t always equipped to handle older, specialized vehicles like a 1999 Mercedes SL 500. The technicians lacked the specific training needed for my car, and the estimated repair costs were high. Choosing a different path, I decided to bring the car home and embrace the challenge of DIY repair.
My initial diagnosis pointed towards either the coil packs or spark plugs as the culprits for the misfire. I began a process of elimination, testing the coil packs by swapping them and using an OBD-II scanner at AutoZone to read the fault codes. This iterative process of changing components and checking codes continued until I pinpointed two cylinders that weren’t firing correctly. Ultimately, replacing all sixteen spark plugs resolved the misfire, and the SL 500 ran smoothly for a while.
However, the repairs were far from over. Replacing the fuel injectors turned into another significant undertaking. Initially, I attempted to just replace the O-rings, but achieving a perfect seal proved incredibly difficult. Frustration mounted until I opted for new injectors complete with fresh O-rings. This job, like many others, was a first for me. During reassembly, things would break – bolts snapping, screws stripping. One particularly memorable instance involved having to drill out a broken screw, a task that was far from enjoyable.
The convertible top hydraulics, which had initially leaked, demanded further attention. Driven by cost considerations, I attempted to rebuild the hydraulic cylinders myself. While significantly cheaper than replacement, I wouldn’t recommend this approach. My DIY rebuild was temporary. The small seals, critical for high-pressure systems, couldn’t be installed as precisely as with professional machinery. For a while, it seemed to work, but as pressure built up with repeated use, a line popped, and fluid sprayed once more. Finally, I conceded and installed remanufactured pistons, a more reliable long-term solution for the 1999 Mercedes SL 500’s complex convertible top system.
One fortunate aspect of the purchase was the inclusion of a hardtop. This proved invaluable when the soft top deteriorated rapidly. Within just a few months, the once-perfect soft top developed holes. To preserve it during good weather, I’d remove the hardtop and store the SL 500 in my parents’ garage, effectively turning it into a fair-weather roadster.
Brake work was another essential maintenance item. I tackled both front and rear brakes, including rotor upgrades. However, even this seemingly straightforward task presented challenges. A seized caliper pin became a major obstacle. Despite applying significant force with a hammer, it wouldn’t budge. Ultimately, I had to take the components to a local Mercedes-Benz dealership. Walking in with car parts in hand, I felt somewhat out of place amidst the other Mercedes owners who simply dropped off their pristine vehicles for service and drove away in loaners. Nonetheless, the dealership’s service department proved invaluable for complex diagnostics. While I preferred to do the repairs myself, their expertise in pinpointing problems was crucial for tackling issues on the 1999 Mercedes SL 500.
One particularly daunting repair involved replacing a leaking intake manifold. This was a major undertaking, requiring the removal of coil packs, spark plugs, and numerous vacuum lines. The reassembly process was nerve-wracking, demanding careful attention to ensure everything was correctly connected. To my immense relief, upon turning the ignition key after reassembly, the engine roared to life. A successful test drive followed, defying my expectations. Completing such a complex repair on the first attempt felt like a significant achievement.
Even routine maintenance presented unexpected moments. When replacing the fuel filter, I neglected to depressurize the fuel system. The result was a face full of gasoline – a messy and memorable learning experience.
Reflecting on my ownership, I wouldn’t recommend a project car, especially a complex Mercedes-Benz, as a first car for novice mechanics. The intricate computer systems and specialized components can make repairs challenging. There were times when I felt I was working on the car as quickly as I could earn money to buy parts. This financial constraint was a primary motivator for tackling the repairs myself.
Despite the challenges and constant repairs, selling the 1999 Mercedes SL 500 was bittersweet. I gained invaluable skills and a deep understanding of automotive mechanics. I went from knowing virtually nothing about cars to possessing a level of knowledge I never anticipated. The entire process ignited a passion for car repair and a specific fascination with the SL and Mercedes-Benz vehicles in general.
Looking ahead, I’m already contemplating my next automotive project. An old Triumph is on my radar, although my 6’4” frame might present a fitment issue. Alternatively, a 5-speed 1992 Mercedes 300SL, in blue, is a dream. The experience with the 1999 Mercedes SL 500, with all its trials and tribulations, has firmly cemented my love for classic cars and the rewarding, if sometimes frustrating, journey of keeping them on the road.
Liam Sullivan is a student at Virginia Commonwealth University studying exercise science.
Piston Car Stories, Preserving Car Culture
