The W123 is the chassis that truly helped put Mercedes-Benz on the map in the United States. For decades this stalwart automobile has been faithfully serving its owners for hundreds of thousands of miles, and even today W123 is not an uncommon sight. It is arguably one of the most durable cars built by Mercedes-Benz, and for this reason alone its popularity still remains strong.
W123 Diesel – The World’s Most Durable Car
A brief buyers guide to the 240D, 300D, and their variants
by Gary Anderson with Mathieu Cama and Pierre Hedary
Contributions from Garrett Goodspeed, Michael Serpe, and Robert Schilling
Originally published in January-February 2010
The W123 is the chassis that truly helped put Mercedes-Benz on the map in the United States. For decades this stalwart automobile has been faithfully serving its owners for hundreds of thousands of miles, and even today W123 is not an uncommon sight. It is arguably one of the most durable cars built by Mercedes-Benz, and for this reason alone its popularity still remains strong.
With the rise of biofuels and the W123 diesel’s reputation for fuel efficiency, a renewed interest in this model has been taking place. Given the newest W123 rolled off the assembly line 24 years ago, the supply of fine examples is limited, though more extensive than anyone might expect. Well-sorted, properly maintained, and unabused examples are becoming harder to find and prices have been rising. However, compared to the price of a new car offering the same mileage, a good W123 is still a bargain, though not valuable enough to justify extensive restoration, and near-derelict examples abound. But with some knowledge of the pitfalls, and the patience to locate a good example, this can be a rewarding and economical car to own.
Background
When new, the W123 was quite a progressive vehicle with many advances over its predecessor, the W115. With the country reeling from the fuel crisis in 1976, demand for fuel-efficient vehicles was at an all-time high when the W123 was launched. The w123 represented the latest in technology and safety. Suspension, serviceability, ergonomics, and appearance were all improved, and the diesel drivetrain was remarkably refined compared to anything produced in the United States. High demand resulted in waiting lists at many dealers.
These vehicles are known to last for hundreds upon hundreds of thousands of miles with maintenance and basic care. Accidents and rust are the primary killers of this venerable model line.
Mercedes-Benz NA officially imported the diesel-powered 2.4-liter 240D sedans, 3.0-liter 300D sedans, 300CD coupes, and 300TD wagons, and the gasoline-powered 4-cylinder 230 and the 6-cylinder 280E and 280CE sedans. The turbocharged 5-cylinder diesel engine, known as the OM617a, made its debut on North American shores in the W116 300SD for the 1978 model year. That engine was then installed in the W123 chassis beginning with the 300TD wagon in the 1981 model year (1983 version pictured on p. 36) and the coupe and sedan for 1982.
Though the 300D is more powerful, a properly driven 240D with a manual transmission can be as rewarding in the switchbacks due to its better handling characteristics resulting from lessweight forward of the front axle.
In 1983, the 240D was replaced by the 190D 2.2. In 1985, increasingly strict emissions requirements killed off the 300D.
Reasons to Buy a W123
- May be the best built, most reliable car from its decade.
- With appropriate care and maintenance, the components may last forever.
- Fewer parts and simpler design than gasoline engines means easier maintenance.
- Self-lubricating, even high-mileage engines don’t require major rebuilds if previously well-maintained.
- Suspension, steering, and braking systems provide competent handling and a comfortable ride.
- Parts are readibly available and components are generally simple to repair.
- Safety, safety, safety. Diesel is not explosive and bodies are designed to absorb collisions while protecting the occupants.
- Excellent space and cargo-carrying capacity, especially in the wagon.
Reasons Not to Buy a W123
- More rust points than most cars.
- Relatively slow, especially by current standards.
- Beware the car with unrepaired body damage, poor shifting and low power, as repairs can quickly drain your wallet.
- Automatic climate control on 1977-1981 models can be troublesome.
- The diesel engine has quirky start-up issues.
Checkpoints
- Rust points include under the battery tray, inner quarter panels behind the rear wheels, floors under the seats, base of the windshield pillars, around the sunroof, along frame rails, door bottoms, rocker panels by jacking points, and at the base of the B-pillars.
- Front sway bar mounts can rust, resulting in detached sway bars and unsafe handling.
- Condition of seat padding and springs, though replacements are readily available.
- A/C system, especially broken compressor clutch, and leaking vacuum actuators for vent controls.
- Rubber bushings and boots on front-end suspension may need replacement. Front sway bar can rust and shear, resulting in unsafe handling.
- Engine operation (listen to a good one for benchmark). Check compression, especially on engines that may have been run on waste vegetable oil.
- Cracked dashboards and peeling wood veneer. Replacement parts don’t exist and good used dashboards are hard to find. Water leaking into the cabin indicates dry or rotten window seals. Look for consequent rust.
- Odometers often fail, so don’t trust claims of low mileage, though high mileage may be no problem.
- Look for signs of inept maintenance, such as patched wiring harnesses, and aftermarket hose clamps on oil cooler lines, as clues to overall problems.
- Check the vacuum system, especially on cars with vacuum modulators on the automatic transmission. Clues: the automatic door locks don’t work or the engine doesn’t shut down when the ignition key is turned off.
Most importantly: Find a good classic-diesel mechanic before you go looking for a good car.
The Nitty-Gritty
Diesel Maintenance: Many folks new to M-B diesels are not aware of the maintenance regimen required for these engines to assure reliability. Motor oil should be changed every 3,000 miles (unless synthetic oils are used and oil condition is monitored through oil analysis), valve clearances checked and adjusted every 15,000 miles, timing chain and sprockets inspected with every valve adjustment and replaced when 7 degrees of stretch is indicated, and the transmission serviced every 30,000 miles. The fuel injectors should be tested at the first sign of a noticeable loss of fuel economy or errant engine sounds, similar to knocking, especially when cold. Out-of-spec injectors should be replaced or rebuilt promptly.
Transmissions: The W123 was introduced with the 722.1xx series automatic transmissions. Properly setup and maintained, they are quite reliable, but finding a technician who has experience with this gearbox may be difficult. The later 722.3xx automatics were more refined and also quite robust. These gearboxes can last more than 300,000 miles with requisite maintenance, proper adjustments, and lack of abuse.
The manual gearbox in the 240D also is robust and long-lasting with routine service and lack of abuse. Second-gear synchronizer and shaft bearings are its weak points. Bearing noise should be addressed immediately to avoid serious damage. Note: Only use ATF in the M-B manual gearboxes. Heavier oils can damage internal components.
Under the Hood: The W123 diesels were available with three different engines in North America: the 4-cylinder OM616, the non-turbo 5-cylinder OM617, and the 5-cylinder turbodiesel OM617a. Throughout the production run a number of changes were made to these motors, but the heart of the internals remained relatively constant. Most power differences came from the injection pumps,
and turbochargers when installed. The early diesels used a York A/C compressor. While it’s a strong performer, repairing it can be complicated because of its brackets and size. The GM-designed R4 compressor installed on 1979 and later models was better. Be wary of stiff linkages on all model years, as they can result in a stuck-open throttle. Cars from ’79 and earlier have a pivot point under the exhaust manifold that is prone to sticking due to the heat and lack of regular maintenance by inexperienced technicians.
Climate Control: The W123 debuted with two different climate control systems. The base system in the 240D was purely mechanical, with three knobs, two controlling heat and one for blower. A fourth knob was used to control the A/C, if so equipped, which would be later replaced with a roller wheel. One or two levers, depending on model year, controlled the direction of air flow. This system may be the simplest and best designed climate control system ever offered on a car.
The 300D was introduced with Automatic Climate Control (ACC). This system is prone to a variety of reliability issues and costly repairs. in 1981, an upgraded ACC system became standard on all U.S. W123s except the 240D, easily identified by the horizontally arranged buttons on the climate control unit. This system is robust but due to age will likely need its vacuum-operated actuators replaced, an expensive but effective procedure.
Turbocharger Kits: Note that the 5-cylinder OM617a, with serial numbers 617.95x, was designed specifically for a turbo application. Be wary of cobbled-together aftermarket turbocharging systems on early 300Ds and 240Ds. 
A Real-World Example by Garrett Goodspeed
In late September of this year, while inspecting my friend John Bronson’s future purchase, a 420SEL, at Willimantic Auto Works in Willimantic, Connecticut, I noticed a 240D sitting on the lot. When I asked Jim, the shop owner, about the 240D, he said it was a 1983 and that he did not own it, but it had been sitting there for over a year after some repairs. The owner of the car worked two jobs and didn’t have time to pick it up; he had mentioned to Jim that if anyone was interested, to tell them the car was potentially for sale. Now Jim is not a dealer, but he told me he would be fine showing me the car. He noted it was a low-mileage car and would looked great if it was cleaned up.
Upon taking a closer look, I saw the car really was “low mileage” with only 63,000 miles on the odometer. When I asked to drive it, Jim popped the hood for the first time in over a year and put a jumper box to the battery. To my relief, it fired right up, no smoke, so quiet, and so smooth. When I sat in the seat, I fell in love. It purred down the road and seemed to have more power than other 240ds I had driven in the past. The air-conditioning compressor even kicked on when I tried it and blew cold! All the car’s power accessories worked to spec, and she even had a working original Becker Europa stereo system. I knew she was the one for me.
After my test-drive, which verified the odometer actually worked, I got out of the car and took a flashlight to look for any rust underneath; none existed. There was no visible rust on the fenders or the jack points. The body underneath the battery tray was rust-free. The floorboards inside and out were perfect, and the trunk did not have any rust inside where leaks would have done damage. When knocking on all the panels and feeling the hollowness due to the lack of any body filler, I couldn’t believe what I had found. Living in New England and being involved with my 300SDL and my girlfriend Caitlyn’s 300CD, I took very good notice of other local older Mercedes and knew what rust could do if the car was not taken care of.
When informed the asking price of $3,500 was firm, I immediately made an offer of that price. A few days later Jim called to tell me he got in touch with the owner and he wanted me to stop by his local fish market to square up financially and pick up the title. The next day, I picked up the car from Jim’s shop. It was a foggy New England morning and the windshield was so dirty I had to stop and clean it with my sweatshirt sleeve. The shirt was ruined, but the car made it safely home.
To most people this car was not anything they would be interested in. It was filthy. So green and covered with dirt and algae from the trees above, it could have been mistaken for many different colors. However I knew how robust these cars were and their paint is no exception. The 050 Classic White cleaned up beautifully. I installed a new set of fuel filters and drive belts, and replaced the engine oil, coolant, and brake fluid. I skipped the transmission fluid and filter because it looked clean and Jim had just done it before it sat. I adjusted the valves in the engine because I didn’t know when they had last been done. I threw in an air filter, and finally my car was roadworthy.
Now this car by no means is a perfect car. I still have to do motor mounts as they are showing their age, brake hoses, and a few minor cosmetic items, such as interior parts and the reattachment of wood trim pieces. But it is a great example of what to look for when purchasing a W123 car.
What about Vegetable Oil?
A myth has developed around the W123 diesels, especially among holistic environmentalists, that the engines can be run on vegetable oil, especially free-for-the-asking waste vegetable oil (WVO) from cooking, just as efficiently and reliably as they can on standard petroleum diesel. Though there is much more to this story (see article starting on page 40), the simple facts are that an older Mercedes-Benz diesel will run on WVO, just not for very long, or very reliably, and may be irreparably ruined in the process, due to clogged fuel lines and injectors, and corroded components. Simply put, unprocessed WVO is contaminated and acidified from frying, can contain water, and generally is hydrogenated with a high glycerin content. These issues will cause the engine to start badly, especially in cold weather, and will eventually cause serious engine damage.
Chronology
Sep. 1975: First examples of the W123 are built for the European market, including the 200, the 230, and the 250 sedans.
Sep. 1976: W115 is replaced by W123 in U.S. market. Four models are available: 240D, 230, 280E, and 300D.
Sep. 1977: 300CD coupe and 280CE join the lineup.
Aug. 1978: 230 is discontinued in the U.S. market.
Sep. 1978: 300TD wagon enters the U.S. market.
Apr. 1979: York A/C compressor is replaced by R-4 A/C compressor on the diesels.
Aug. 1979: Electronic glow plug system is released and horsepower increased.
Sep. 1979: Mechanical linkage automatic transmission is replaced by modulator-only transmission on all non-turbo models.
Sep. 1980: 300TD turbodiesel wagon is released. Turbo-diesels get 722.3 transmission. Third-generation Automatic Climate Control introduced.
May 1981: 300CD gets a turbodiesel engine.
Sep. 1981: 300D gets a turbodiesel engine.
Sep. 1982: Interior, seats, and carpeting, upgraded on all models.
Sep. 1983: 240D is discontinued.
Aug. 1984: 300D [and all variants] receive upgrades to the differential [2.88:1 ratio is used], vacuum system and turbocharger.
Vacuum controls are refined and a different torque converter installed on 722.3 transmission.
California market cars receive trap oxidizer and 722.4 transmission [all other models retain older 722.3 gearbox].
Sep. 1985: W123 production for the U.S. market ceases.
Jan. 1986: W123 production in Europe ceases.
Value Estimates
A low value corresponds to a poorly kept car, useful only for parts,
an average car has some needs [$2,000-$4,000 worth],
and a high-value car needs little to be safe and attractive.
Prices will fluctuate with location as well as condition.
Low Medium High
230 sedan, 280E, ‘75-’78 $500 $2,500 $4,500
280E, 280CE, 280TE
[European only] $500 $2,000-$4,500 $4,500-$8,500
300D [non-turbo] $600-$1,100 $1,800-$2,100 $5,500-$6,000
300CD, 300TD [non-turbo] $1,000 $3,500-$4,000 $5,500-$7,500
240D, auto and stick $800 $2,400-$4,000 $6,000-$8,500
[some 4 speeds]
300D turbo $1,500 $3,000-$5,500 $7,500-$9,500
300CD, 300TD turbo $1,800-$2,300 $4,500-$6,500 $8,000-$15,000
Exceptions
European diesels with $1,500-$1,800 $3,200-$3,500 $8,500-$10,000
manual gearboxes,
or 5-speed 280E
W123 Models by the Numbers
Years and Production
230 75-81 196,285
240D 75-85 454,780
300 75-85 331,999
300CD 77-81 U.S. 7,502
300D turbo 81-85 U.S. 75,261
300TD 77-86 36,874
300TD turbo 79-86 28,219
300CD turbo 81-85 U.S. 8,007
W123 Specifications (vary by models)
Transmission 4-speed auto
Wheelbase 110.0 in
Weight 3,515-3,430 lbs
Wheels 14x6J
Tires 195x70R-14
Brakes 4-wheel discs
10.9 in front discs
11.0 in rear discs
0-60mph approx. 22 sec
Max. speed 85 mph
Fuel economy 23 city/
(300D) 28 hwy
Engines
300 617.912 5/77-9/81
5-cylinder inline diesel non-turbo
Displacement 3,005cc
Compression 21.0:1
Max power 77 hp @ 4,000 rpm
(1980-’81) 83 hp @ 4,200 rpm
Max Torque 115 lb/ft @ 2,400 rpm
(1980-’81) 120 lb/ft @ 2,400 rpm
300 turbocharged 617.952 9/81-8/85
5-cylinder inline turbo diesel
Displacement 2,998cc
Compression 21.5:1
Max Power 120@ 4,350 rpm
(1984-’85) 123hp@ 4,350
(Calif ‘84-85) 118 hp@ 4,350 rpm
Max Torque 170 lb/ft@ 2,400 rpm
(1984-’85) 184 lb/ft@ 2,400 rpm
(Calif ‘84-85) 177 lb/ft @ 2,400 rpm
References
- Illustrated Mercedes-Benz Buyer’s Guide by Frank Barrett, out of print but avail. through Toad Hall Books.
- Mercedes-Benz Production Models 1946-1990 by W. Robert Nitzke, Motorbooks 1990.
- www.mbca.org/forums
- Mercedes-Benz Buyer’s Guide by Fred Larimer. Motorbooks, 2004.
- Standard Catalog of Mercedes-Benz by Jim Luikens. Krause Pubs, 2008.
- www.mercedesheritage.com