The Mercedes-Benz W116, a true icon of automotive engineering, represents a golden era for the German marque. Recently, I had the pleasure of spending some quality time wrenching on a 1980 Mercedes-Benz 280SE (W116 chassis), equipped with the robust DOHC M110 inline-six engine. This experience provided a valuable, hands-on perspective on the realities of owning and maintaining these classic machines. While my particular model presented itself with a seemingly low 75,000 miles – a figure immediately suspect due to a slipping odometer upon acquisition – several factors hinted at the mileage being closer to accurate. The immaculate MB-Tex interior, save for typical sagging springs and horsehair pads, the pristine original spare tire in the trunk still holding air, and remarkably well-preserved plastic door sills all suggested a life less travelled. Furthermore, the car’s straight body, requiring only minor TLC, reinforced the impression of an unblemished history, a rarity in the world of vintage vehicles, and something I increasingly value.
Uncovering Common W116 Issues: Radiator Leaks and the Infamous AC Servo
Delving into the mechanics of this Mercedes-Benz W116 280SE quickly revealed a couple of common ailments that plague these models. Beyond the expected radiator leak, the notorious AC servo had succumbed to cracking and leaking. It’s a well-known issue within the W116 community, so much so that a specialized cottage industry has sprung up around this problematic, and often expensive, component. Ebay is rife with listings catering to this specific W116 weakness.
For my 280SE, the solution involved a radiator recore for reliable cooling. For the AC servo, I opted for George Murphy’s renowned aluminum-housed version – a durable and intelligently engineered upgrade. Installing it myself, while meticulously cleaning up the corrosive coolant residue that had spread throughout the area, was a straightforward process thanks to George’s excellent guidance and clear explanations provided with the servo. I wholeheartedly recommend his solution as the most sensible approach to this common Mercedes-Benz W116 problem. While addressing the cooling system, I also proactively replaced the amplifier (located behind the dashboard) and the auxiliary coolant pump (adjacent to the AC servo). The amplifier replacement might have been preemptive, but the auxiliary pump was exhibiting a noticeable whine, and someone had bypassed its temperature switch (also behind the dash). Rectifying these issues and restoring the system to its original configuration ensures optimal cooling performance for the W116.
This common coolant leak issue, stemming from the AC servo in Mercedes-Benz W116 models, likely contributes to the unfortunate number of these cars ending up in junkyards. The gradual coolant loss can go unnoticed, leading to overheating and severe engine damage – warped aluminum heads and blown head gaskets being common consequences. This could explain the high turnover of W116s in salvage yards, a trend observed years ago with the earlier W108 models. Even experienced mechanics often remark on the surprisingly low mileage of surviving W116s, acknowledging their potential if properly maintained, but also noting the scarcity of well-preserved 280SE models compared to the more frequently seen, and often higher mileage, 450SE variants.
With the cooling system overhaul complete, my Mercedes-Benz W116 280SE now maintains a steady temperature just above 80 degrees Celsius, and the air conditioning functions flawlessly – a true blessing, especially in warmer climates.
Tackling Vacuum Leaks and the Trunk Seal on a W116
Another typical issue encountered with older Mercedes-Benz models, including the W116, is vacuum leaks in the door locking system. In my 280SE, the culprit was the actuator in the rear passenger door. Diagnosing such leaks can be done methodically. If, after leaving the car unlocked for a period, all door lock plungers drop upon locking, it indicates a leak in one of the diaphragms responsible for pulling the locks closed. Furthermore, a telltale sign is the gas door lock sliding open shortly after locking the car, due to the system losing vacuum pressure. This is a clever design feature to prevent being stranded without fuel if the vacuum system fails entirely. A temporary fix involved plugging the vacuum line to the faulty actuator, which effectively resolved the leak in the interim, maintaining vacuum for days.
Replacing the trunk seal on a Mercedes-Benz W116 is another time-consuming but essential maintenance task to prevent water ingress. After meticulously cleaning the old adhesive from the channel, I used black 3M Weatherstrip Adhesive for the new seal. While striving for the precision of the original Sindelfingen factory installation, achieving perfection can be challenging. The trunk seal design incorporates a lip that directs water flow into the channel, and two joints within the seal require careful alignment, particularly a specialized section intended to align with the rear deck of the lid. The seal’s cross-section, which curls under the lid, is deliberately deeper to ensure a tight, weather-proof closure. Over years, this curling action can become permanent compression, leading to leaks even if the seal appears visually intact. Installing the new seal in approximately 18-inch sections, and removing the lower plastic shield along the perimeter, facilitated easier installation around the taillights. Using a generous supply of vinyl gloves is crucial to avoid adhesive mishaps.
However, the new trunk seal presented an unexpected challenge. Its increased grip caused it to fold incorrectly in places, hindering proper closure. Initially, talcum powder was used to improve slippage along the trunk lid, offering some improvement but proving insufficient. The breakthrough came with the idea of using strings placed in the trunk while open, to be pulled out after closing. This technique aimed to grab the seal’s lip and flip it into the correct “curl out” position. While the effectiveness of this method was difficult to ascertain visually due to the seal’s deep recess, it was a creative approach to address the issue. Further refinement involved using ribbed rubber cord, typically used for window screens, to provide enhanced grip and hopefully achieve the desired seal positioning.
Odometer Repair: Restoring Accuracy to the W116 Instrument Cluster
Addressing the slipping odometer was another key project for this Mercedes-Benz W116 280SE. A crucial tip for anyone undertaking instrument cluster removal: protect the dashboard and steering column with tape. The cluster can be unwieldy during removal. Loosening the speedometer cable under the dash beforehand is also recommended. Investing in plastic trim and molding removal tools from Harbor Freight proves invaluable for gentle and scratch-free disassembly. Despite these precautions, the gasket on my cluster was damaged, necessitating a replacement sourced from a pick-n-pull, which was then reconditioned with vinyl protectant. Documenting connector locations and being mindful of the cruise control stalk during removal are essential.
Once removed, following online guides, such as the excellent resource at dieselgiant.com (http://www.dieselgiant.com/repairyourodometer.htm), is highly recommended. The diagnosis in my case mirrored the guide’s findings: the pot metal gear at the end of the odometer gear train was slipping on its shaft. The repair involved pushing out the shaft with a drill bit, roughening the end to improve friction, and then forcefully re-seating the gear. Creating a makeshift splined effect provided sufficient grip to prevent further slippage. Despite attempts to apply Loctite, achieving adequate penetration proved impossible. However, testing the repaired odometer by manually adding several hundred miles, observing its consistent and reliable flipping of digits, confirmed the repair’s success. After cleaning and testing all instrument cluster lights, reinstallation restored accurate mileage tracking to the W116.
Performance Observations and Future W116 Projects
Post-repair, some interesting performance characteristics emerged. The fuel economy of the 280SE proved to be comparable to the larger 450SE, despite possessing significantly less power.
Looking ahead, several maintenance and improvement projects are planned for this Mercedes-Benz W116 280SE. Valve adjustment, new tires, steering box adjustment, and windshield replacement are on the immediate horizon. Furthermore, two unresolved issues require attention: a hot start problem and late transmission shifting. Initial research points towards the fuel pressure accumulator as a potential cause for the hot start issue, while transmission troubleshooting is ongoing, seeking insights within online forums and resources.
The Enduring Appeal of the Mercedes-Benz W116
Despite the typical challenges associated with owning a classic Mercedes-Benz W116, particularly a model of this vintage, the experience is undeniably rewarding. Addressing these common issues, from cooling system vulnerabilities to vacuum leaks and odometer malfunctions, brings a deeper appreciation for the engineering and enduring quality of these vehicles. The Mercedes-Benz W116 remains a compelling choice for classic car enthusiasts, offering a blend of timeless design, robust mechanicals, and a rewarding DIY ownership experience.
