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Getting an Education from a 1999 Mercedes SL500

In the past, many car enthusiasts learned skills years before they were old enough to work and purchase their own cars. Today, the stories are different and Liam Sullivan’s healthy dose of determination served him well to keep his first car on road, running well and safe.

By jeff mason

May 28, 2021

I saw the 1999 Mercedes SL500 at my Uncle Dave’s shop in New Hampshire when I was visiting him and my Aunt Kate. It needed work but it was a beautiful car and I thought, if I’m going to buy a car, why not a pretty one?

The car was a year older than me and had 121,000 miles on it but my mindset was, once I have it, if there is a problem, I can deal with that problem.

I was able to buy it with the money I’d earned and saved, then started the long drive home to Virginia, stopping in Massachusetts to visit my Aunt Karen and Uncle Erik. During that visit, the hydraulics for the pistons that control the locks for the convertible top started spraying fluid. I borrowed some paper towels and got the mess cleaned up. I was lucky. Of all the leaks that happened in the car, nothing ever got on the carpet.

After I left Massachusetts, the engine started misfiring but I didn’t know what that meant. That model has 16 spark plugs for eight cylinders so it’ll still drive okay with a bad plug because every cylinder will still fire. When I got home, I opened the hood because I was curious about what was going on.

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.

I took the car to a shop to get them to read the codes and learn why the check engine light was on. I discovered that a shop that works on daily drivers isn’t always the best place to take an old car. The techs at this shop didn’t have the training to work on my car. I decided against having the work done there for that reason and for cost. Instead, I brought the car home and decided I could figure this out on my own.

I knew it’d be either the coil packs or the spark plugs so I started to test the coil packs by switching them out and resetting the codes. Then, I’d go to AutoZone to have them read the new codes that came up. I just kept changing stuff around and going back and forth until I found two sparks that weren’t firing. I replaced all the spark plugs and the car drove well for a while.

While I owned it, I also needed to change the fuel injectors, which was a nightmare. I tried to replace the O rings but they needed to seat just right. In the end I bought new injectors with new O rings. This was the first time I’d ever done any of this work and things would break when I reassembled the car, like bolts. Once, I had to have a screw drilled out. That was not great.

Liam Sullivan's Mercedes project car.

I ended up rebuilding the hydraulic cylinders for the convertible top. It was way cheaper but I wouldn’t recommend doing that. It worked for a while but I couldn’t install the small seals as well as a machine can and the pressure inside is very high. I crossed my fingers and hoped. I started using the top and the pressure built up, popping a line and spraying fluid again. I finally ordered and installed remanufactured pistons.

When I bought the car, it came with a hard top, which was nice because, after the soft top wore out, I didn’t have the money to replace it. I was driving the car daily and things wore out. The top went from perfect to having holes in the span of a few months. If there was a set of nice days, I’d remove the top and park in my parents’ garage.

I also did the brakes, front and rear. Upgrading the rotors was another nightmare because the caliper pin had seized. I tried hitting it with a hammer as hard as I could. I ended up taking the parts to a local Mercedes dealer. The guy looked at me like I was crazy when I brought him the piece of the car to ask for help. The other Mercedes owners were just dropping off their cars and leaving in loaners. I took mine there a few times for major diagnostic help. I could do whatever work the car needed but I wanted them to tell me what was wrong.

At one point, the intake manifold was leaking a lot of air. Replacing the manifold was a huge job. I had to undo all the coil packs, spark plugs, and then remember where everything was plugged in during reassembly. Undoing the vacuum lines was scary. When the job was done, I turned the ignition key and the engine ran. I was so surprised. During the test drive, I expected the engine to fall out. There was no way this worked on my first try with something this complex but it did.

When I replaced the fuel filter, I forgot to depressurize the system and got hit in the face with fuel. That was an experience.

I wouldn’t recommend a project car as a first car, definitely not a Mercedes because the computers make thing so complex. At a certain point, I was fixing the car as fast as I made money to do the work. That was the main reason I did the work myself because I could barely afford the parts.

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. I became really interested in the process of repair and learned everything about the SL and cars in general.

I’ve already started looking for another car. I’m thinking of buying an old Triumph but I’m 6’4” and might not fit in it. Or, I’d love a 5-speed 1992 Mercedes 300SL, blue on blue on blue.

You can learn a lot from a 1999 Mercedes SL500

Liam Sullivan is a student at Virginia Commonwealth University studying exercise science.

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