Mercedes-Benz W123 Diesel Owners Repair Guide

Youtube Video:

Maintenance Guide For Your W123 Diesel
If you own a Mercedes-Benz 240D, 300CD, 300D, 300SD, 300TD or any vehicle with a OM615, OM616 and OM617 Engine, then this guide is for you. Lack of maintenance is the most common reason for a catastrophic failure on old and high mileage vehicles. By following this guide and performing the recommended maintenance, you can avoid costly repairs and keep your vehicle running strong for years to come.

The Importance of Maintenance
It is important to perform the recommended maintenance on your vehicle in order to avoid costly repairs. Over time, parts will wear out and fluids will break down. By replacing these parts and fluids on a regular basis, you can prevent major issues from developing. Many people wait until something breaks before they take their car in for service. But by then, it is often too late and the damage has been done. It is much cheaper to perform preventive maintenance than it is to wait for something to break and then pay for the repairs.

By following this maintenance guide and performing the recommended service on your W123 Diesel, you can avoid costly repairs and keep your vehicle running strong for years to come. Regular maintenance is much cheaper than waiting for something to break and then paying for the repairs. So don’t put it off any longer! 

Mercedes-Benz W123 - The Best Car Ever Built?

The Mercedes-Benz W123 is a range of cars produced by German manufacturer Mercedes-Benz from November 1975 to January 1986. The W123 models surpassed their predecessor, selling 2.7 million units before the production ended in the autumn 1985 for saloon/sedan and January 1986 for coupé and estate/station wagon.

Like its predecessors, W123 gained the reputation of being over-engineered, well-built, durable, and reliable. Many taxi companies chose W123 for this reason, and they were common sight in Germany. Reaching 500,000 or 1,000,000 km with minor mechanical issues. Once the W123 reached the end of service life, they were often shipped to Africa and third world countries where they were highly esteemed for ability to travel on rough roads and further without frequent maintenance.

What made the W123 so successful? Let’s take a look.

The W123 was designed with longevity in mind. Every aspect of the car was built to withstand years of abuse and still come out looking good. This is evident in the simplistic design which features clean lines and elegant curves. The purpose of this design was to make the car as aerodynamic as possible which helped reduce fuel consumption. Furthermore, the use of high-quality materials ensured that the car would age gracefully even after years of use.

One of the main reasons why the W123 is so highly regarded is because of its reliability. These cars were built to last and many owners have attested to this fact. In fact, it’s not uncommon to see W123s with over 500,000 kilometers on the odometer still going strong. This is a testament to Mercedes’ commitment to quality and engineering excellence.

Ride Quality
Another area where the W123 shines is ride quality. These cars are incredibly comfortable even by today’s standards. The suspension is soft but not too soft and soaking up bumps is never an issue. The steering is light but precise which makes driving around town a breeze. At higher speeds, the car remains remarkably composed and stable thanks to its excellent aerodynamics. All in all, the ride quality is unbeatable even after 35 years . . .

If you’re looking for a used car that will give you years of trouble-free service, then you can’t go wrong with a Mercedes-Benz W123. These cars are some of the most well-built and reliable machines ever made thanks to their over-engineered design and use of high-quality materials throughout. furthermore, they’re still incredibly comfortable to drive thanks to their excellent ride quality. So if you ever have a chance to own one of these classics, be sure to jump at it!

W123 Model Designations

Mercedes-Benz used a series of internal chassis codes to denote the weight, engine type, and chassis configuration of each model. The table below shows the model designations that correspond to the engine displacement, chassis type (coupé or estate/station wagon), fuel type (for diesel engines only), and availability of fuel injection system (for petrol engines only).

  • C for Coupé
  • T for Tourismus und Transport (estate/station wagon)
  • No designation was given for the long-wheelbase: it was simply called "Lang" (long) in the brochures and order forms.
  • D for Diesel
  • E for Einspritzung (fuel injection)
  • When the diesel engine is turbocharged, TURBODIESEL is affixed to the right side of the boot lid.

As for the chassis codes, W123 is the saloon/sedan, S123 the estate/station wagon, C123 the coupé, V123 the long-wheelbase saloon/sedan a.k.a. Lang, and F123 refers to the bare long-wheelbase chassis as used for ambulances and other conversions.

With so many options available, it can be difficult to keep track of all the different model designations used by Mercedes-Benz. However, by understanding what each designation corresponds to, you can better choose the model that is right for you. If you have any questions about which model might be right for you, feel free to contact your local Mercedes-Benz dealer for more information.

 The world's first turbocharged diesel engine for passenger vehicle

The world's first turbocharged diesel engine for passenger vehicle, OM617 A was finally introduced in W123 models in September 1979, exclusive to 300 TD TURBODIESEL for European market. The same engine is offered in the North America and Japan in 1981 as 300D TURBODIESEL, 300CD TURBODIESEL, and 300TD TURBODIESEL.

Maintenance and Inspections:

  1. Inspect or replace the air filter
  2. Oil Change
  3. Inspect or replace Belts
  4. Diesel Purge to clean out the fuel system. After the purge change the Fuel Filters. There are 3 Filters. Primary(Large Spin On) Secondary(Inline Filter) Tank Screen(Strainer Type) The tank screen can be cleaned but if its too dirty it must be replaced. Inspect for any fuel leaks while the car is running. The rubber fuel injector return lines are common to leak.
  5. Valve Adjustment!!! It is very important to do a valve adjustment. Its recommended to be done every 12-15K miles or 1 year. If you dont know when it was done last just do it anyways.
  6. Hard Starts or white smoke on start up is a sign the Glow Plugs or injectors need to be replaced. I recommend to use a reamer to clear the carbon from the chambers, this helps improve glow plug life. 
  7. Injectors! I recommend having your Injectors Rebuilt. You can also buy new ones.
  8. Flush the radiator with a process called Citrus Flush. Refill with MB Coolant or Zerex G-O5. Green Coolant is Harmful to the cooling system!
  9. Check or Adjust IP Timing
  10. Inspect Timing Chain Stretch
  11. Check The Lug Bolts
  12. Inspect or replace the Motor Mounts and Engine Shocks
  13. Vacuum Leaks can cause the car to not shut off, the door locks will not work, transmission shifting issues and more. Check all your vacuum lines are connected and the rubber connectors are not torn. 
  14. Clean or Delete the EGR System
  15. Check Or Replace Rear Diff Fluid, Transmission Fluid, Power Steering and Brake Fluid
  16. Check brake pads and inspect Control arm bushings and steering components for torn rubber boots. Grease if applicable. 
  17. Inspect the brushes on the Voltage Regulator it is recommended to inspect them every 50K. Replace when the brushes are near 5mm or Every 100k Miles.