The W123 chassis is well-known and loved by Mercedes enthusiasts. Although Mercedes stopped producing these cars decades ago, many owners still keep them on the roads. These vehicles are relatively reliable, including the turbocharged diesel engines found in models denoted with a 'D.' However, servicing an older diesel engine requires a little more care than you might expect.

If you've recently acquired one of these vehicles, it's crucial to understand the steps you'll need to take to keep it running well. While there's plenty of routine maintenance, two of the most critical items are the fuel and air filters. If you're used to maintaining more modern vehicles, you may be surprised at how important these items are on an older diesel engine.

What Do These Filters Do?

Diesel engines work a little bit differently than gasoline engines. Gasoline engines rely on a spark plug to ignite the fuel and air mixture, while diesel engines rely on the heat generated by compression. Your car's diesel engine uses a far higher compression ratio than gasoline engines, creating substantially more heat. As a result, the diesel fuel ignites when it encounters this hot, compressed air.

Your air filter must remain clean and unclogged because of this high compression ratio and the need to draw in large amounts of air. A restricted air filter can substantially impact the performance and efficiency of your engine. When replacing the filter, it's essential to avoid allowing dust, debris, or other contaminants to pass through the filter housing and into the engine.

Likewise, your fuel filter plays an essential role in protecting your engine from contaminants, including the moisture that can build up in diesel fuel. W123 Mercedes cars include a primary and secondary fuel filter. Surprisingly, the primary filter is smaller while the secondary is much larger. Both filters screen out particulate matter and moisture, and both require routine replacement.

What Happens If You Don't Change Your Filters?

Both your air and fuel filters can become dirty and restrict your engine's access to these vital resources. In extreme cases, old filters can wear and break down, allowing fine particulate matter into your engine. These particles can cause internal engine damage, ultimately resulting in a repair bill that will be drastically more expensive than a routine filter change.

It's also important to remember that every W123 Mercedes is several decades old, and most have a significant number of miles on their engines. As engines age, they require more care to maintain and can become more sensitive to deferred maintenance. Keeping up with these routine service jobs is an excellent way to ensure you can continue to enjoy your classic Mercedes for many more years.

For more information or for assistance, take your car to a local Mercedes service.