The Mercedes-Benz W126 is celebrated for its robust build and luxurious features, but not all models within this esteemed S-Class generation are created equal. For enthusiasts considering a gasoline-powered W126, the advice is often straightforward: opt for a V8. This perspective stems from experiences, particularly with models like the Mercedes 300se, which, while possessing the inherent W126 qualities, presents certain drawbacks, especially concerning fuel economy and overall driving experience.
One owner candidly shares their long-term experience with a 300SE, highlighting some key areas where this model falls short, especially when compared to its V8 counterparts or even diesel alternatives within the W126 range. The primary concern raised is the underwhelming fuel economy. Despite running on readily available 87 octane gasoline, the 300SE struggles to deliver respectable mileage. City driving sees figures as low as the low teens (miles per gallon), climbing to a mediocre 20-21 mpg on the freeway at around 65mph. This owner bluntly describes these figures as “lame,” pointing to the car’s inherent inefficiencies, potentially stemming from poor weight distribution and less-than-ideal gearing.
The lack of a five-speed manual transmission in imported models is noted as a missed opportunity that could have potentially improved fuel efficiency and driving dynamics. The owner suggests that the automatic transmission’s programming, which starts V8 models in first gear but doesn’t optimize gear selection for the inline-six 300SE, contributes to the issue. Furthermore, factors like mistimed camshafts and vacuum leaks, common in older vehicles, are also mentioned as potential culprits exacerbating fuel consumption problems in the Mercedes 300SE.
Beyond fuel economy, the cooling system of the Mercedes 300SE is also brought into question. The owner suggests that the radiator size, smaller than those in other W126 models, combined with the hose configuration, might hinder effective heat dissipation. This, coupled with the car’s clutch fan system, allegedly leads to higher operating temperatures, particularly in warmer climates. The fan clutch is reported to remain engaged almost constantly when the air conditioning is in use, further impacting the engine’s performance and contributing to a sluggish driving feel, especially during summer months.
While acknowledging that the Mercedes 300SE is not prone to overheating, the elevated temperatures are still seen as a notable drawback, affecting overall performance and potentially longevity of components. The driving experience is described as “absolute slug to drive in the summer,” and only “so-so” on the freeway at moderate speeds (60-65mph) due to engine noise or “buzzing.” Based on these experiences, the owner explicitly states they would “never buy another M103+W126 car,” referring to the combination of the M103 inline-six engine found in the 300SE and the W126 chassis.
Despite these criticisms, the owner’s continued ownership of their high-mileage Mercedes 300SE (nearly 300,000 miles) speaks to the inherent reliability and simplicity of the inline-six engine. They note having rebuilt or replaced “just about everything” on the car, emphasizing its straightforward mechanics. The fact that “everything works and starts every day,” even with such high mileage and original engine components exhibiting good compression, underscores the inherent durability often associated with Mercedes-Benz vehicles of this era.
For those prioritizing fuel economy and a more relaxed driving experience, especially for commuting, the owner recommends considering the 300SD, the diesel variant of the W126. This implicitly reinforces the initial advice: for a gasoline W126, the V8 models are generally preferred, while diesel versions offer a different set of advantages, potentially making the Mercedes 300SE the least desirable option within the W126 lineup for certain buyers focused on performance and efficiency.
