Mercedes W123

Generations (what actually changed)

Because there is only 1 generation, “which generation to buy” is not a comparison: you are buying this Coupe run. What you *do* choose is cylinder count (4, 5, or 6), fuel (Gasoline vs Diesel), feed (Carburetor vs Distributed injection (multi-point)), and Manual vs Automatic.

1 generation (1975-01-01 to 1985-12-31): body Coupe. Every version below shares that window. Ground clearance is 165 mm on every version where it is listed. Fuel tank is 65 L on every version. Drive is RWD on every version. Boost is No on every version. Wheel size is not measured on every version. CO2 and eco class are not measured on every version.

Because there is only 1 generation, “which generation to buy” is not a comparison: you are buying this Coupe run. What you do choose is cylinder count (4, 5, or 6), fuel (Gasoline vs Diesel), feed (Carburetor vs Distributed injection (multi-point)), and Manual vs Automatic.

Engines and specs

Same name, different cars: three 2.3 AT / wait — two 2.3 AT (136 hp vs 109 hp); three 2.8 AT (156 / 177 / 185 hp); two 2.8 MT (185 hp 2746 cc vs 177 hp 2800 cc). Always use horsepower (and displacement where needed) as the disambiguator.

Power per litre (hp ÷ displacement in litres):

• 2.3 MT4 / 2.3 MT5 / 2.3 AT (136 hp): 136 ÷ 2.299 ≈ 59.2 hp/L
• 2.3 AT (109 hp): 109 ÷ 2.307 ≈ 47.2 hp/L (the weakest Gasoline specific output)
• 2.8 AT (156 hp): 156 ÷ 2.746 ≈ 56.8 hp/L
• 2.8 MT (185 hp, 2746 cc) and 2.8 MT5: 185 ÷ 2.746 ≈ 67.4 hp/L (highest measured specific output)
• 2.8 AT (177 hp) and 2.8 MT (177 hp): 177 ÷ 2.800 ≈ 63.2 hp/L
• 2.8 MT4 and 2.8 AT (185 hp): 185 ÷ 2.800 ≈ 66.1 hp/L
• 3.0 AT: 84 ÷ 2.998 ≈ 28.0 hp/L (Diesel; about 2.4× lower than the 67.4 hp/L 2.8 MT5)

Feed split that actually moves the numbers: Distributed injection (multi-point) on the 136 hp 2.3 trio and on the 185 hp 2746 cc sixes; Carburetor on 2.3 AT (109 hp) and 2.8 AT (156 hp). The 2800 cc sixes are injection but leave torque, 0–100, and mpg not measured.

Performance and economy

Fastest measured: 2.8 MT (185 hp, 2746 cc) and 2.8 MT5 at 9.9 s and 200 km/h. Slowest measured: 3.0 AT at 19.2 s and 150 km/h — 9.3 s slower and 50 km/h slower than those 185 hp manuals.

The extra fifth gear does not change 0–100 or top speed on the fours or the sixes; it only changes highway and mixed fuel use:

• 2.3 MT5 vs 2.3 MT4: highway 7.7 vs 8.1 (−0.4 L/100 km), mixed 9.6 vs 10.3 (−0.7). City stays 13.1.
• 2.8 MT5 vs 2.8 MT (185 hp, 2746 cc): highway 8.5 vs 9.3 (−0.8), mixed 10.7 vs 11.7 (−1.0). City stays 15.

Automatic cost on the same 136 hp 2299 cc engine: 2.3 AT (136 hp) is 0.8 s slower to 100 than 2.3 MT4 (12.3 vs 11.5), 5 km/h slower on top (175 vs 180), mixed 11 vs 10.3 (+0.7). Highway 8.6 vs 8.1 (+0.5). City is the same 13.1.

Injection vs carburetor on 2.3 AT: the 136 hp injection car vs the 109 hp carburetor car is +27 hp, +20 Nm (205 vs 185), −2.4 s to 100 (11.5 is the MT figure; AT-to-AT is 12.3 vs 13.9 = −1.6 s), top speed 175 vs 165 (+10 km/h), mixed 11 vs 13.7 (−2.7 L/100 km). Fuel grade 95 vs 92.

2.8 AT (156 hp, Carburetor) is the thirstiest measured mixed figure at 14 L/100 km — 4.4 L more than 2.3 MT5 (9.6) for only 20 hp more than the 136 hp fours (156 − 136 = 20) and a 0–100 of 11.3 s, which is only 0.2 s quicker than 2.3 MT4 (11.5). That is a poor performance-per-litre trade on these numbers.

Diesel 3.0 AT fuel use is not measured, so you cannot pick it on mpg from this catalogue; you can only pick it on 84 hp, 163 Nm at 2400 rpm, 19.2 s, 150 km/h, and 1550 kg.

Dimensions and weight

Kerb range among measured cars: 1375 kg (2.3 AT 109 hp) to 1550 kg (3.0 AT) — 175 kg. Gross: 1850 to 2050. Clearance and tank do not change, so they do not help you choose a version. Wheels cannot help you choose: not measured.

kg per hp (kerb ÷ hp), measured only:

• 2.3 AT (109 hp): 1375 ÷ 109 ≈ 12.6 kg/hp
• 2.3 MT4 / 2.3 MT5 / 2.3 AT (136 hp): 1380 ÷ 136 ≈ 10.1 kg/hp
• 2.8 AT (156 hp): 1445 ÷ 156 ≈ 9.3 kg/hp
• 2.8 MT (185 hp, 2746 cc) / 2.8 MT5: 1460 ÷ 185 ≈ 7.9 kg/hp (lightest per horsepower)
• 3.0 AT: 1550 ÷ 84 ≈ 18.5 kg/hp (heaviest per horsepower; about 2.3× the 7.9 figure)

Front and rear suspension where measured: Independent, spring / Independent, spring. Front and rear brakes: Disc / Disc. Rear suspension on 2.8 AT (177 hp), 2.8 MT (177 hp), 2.8 MT4, 2.8 AT (185 hp) is not measured. Engine position on those four 2800 cc cars is not measured. Valves per cylinder on those four: not measured. Compression on those four: not measured. Bore × stroke on those four: not measured.

Which version to choose

Buy 2.8 MT5 if the numbers that matter are speed and highway mpg among the sixes. It matches 2.8 MT (185 hp, 2746 cc) at 185 hp, 240 Nm, 9.9 s, 200 km/h, 1460 kg, and beats it by 0.8 L/100 km on highway and 1.0 mixed. Same Distributed injection (multi-point), 95 fuel, 6 Inline, Manual. The only measured cost of the fifth gear vs 2.8 MT (185 hp, 2746 cc) is not power — it is not measured as a power change — it is the extra ratio, and the data show that as fuel, not as 0–100.

Buy 2.8 MT (185 hp, 2746 cc) if you want the same peak figures with a 4-speed Manual. 0–100 and top speed are identical to 2.8 MT5. You pay +1.0 mixed L/100 km. If you prefer four ratios, this is the measured performance peak.

Buy 2.3 MT5 if you want the cheapest-to-run measured Gasoline Coupe. Mixed 9.6 is the lowest measured consumption in the set; highway 7.7 is the lowest highway figure. You give up 49 hp vs 2.8 MT5 (185 − 136) and 1.6 s to 100 (11.5 vs 9.9), plus 20 km/h of top speed (180 vs 200). Kerb is 80 kg lower (1380 vs 1460). Specific output 59.2 hp/L vs 67.4. For mixed-cycle economy, 2.3 MT5 beats 2.8 MT5 by 1.1 L/100 km (10.7 − 9.6).

Buy 2.3 MT4 only if you specifically want 4 Manual gears on the 136 hp four. Same 136 hp, same 11.5 s, same 180 km/h, same 1380 kg as 2.3 MT5. The measured penalty is +0.4 highway and +0.7 mixed. There is no performance gain for dropping the fifth gear.

Buy 2.3 AT (136 hp), not 2.3 AT (109 hp), if you need Automatic on a four. Same name, different engines: 2299 cc injection 136 hp vs 2307 cc carburetor 109 hp. The 136 hp AT is 27 hp stronger, 1.6 s quicker (12.3 vs 13.9), 10 km/h faster (175 vs 165), mixed 11 vs 13.7. Kerb is only 5 kg higher (1380 vs 1375). Choosing the 109 hp 2.3 AT saves almost no weight and loses the most Gasoline performance in the table.

Avoid 2.8 AT (156 hp) if you are shopping with a calculator. Versus 2.3 AT (136 hp): +20 hp, +0.2 s better than 2.3 MT4 but versus the 136 hp AT it is 11.3 vs 12.3 (−1.0 s), top 185 vs 175 (+10), mixed 14 vs 11 (+3 L/100 km), city 17.7 vs 13.1 (+4.6), kerb +65 kg. You also drop from Distributed injection (multi-point) to Carburetor and from 95 to 92. The 156 hp six is slower than 2.8 MT5 by 1.4 s and 15 km/h, and uses 3.3 L more mixed (14 vs 10.7).

Treat the four 2800 cc names as incomplete spec sheets, not as proven upgrades. 2.8 AT (177 hp), 2.8 MT (177 hp), 2.8 MT4, and 2.8 AT (185 hp) list 2800 cc, 6 Inline, Gasoline, Distributed injection (multi-point), 92 fuel, RWD, No boost, tank 65, clearance 165. Torque, 0–100, top speed, fuel use, kerb, and gross are not measured. You cannot claim they are quicker or thriftier than the 2746 cc cars because those deltas are not measured. If you need numbers you can compare, stay on 2746 cc 2.8 MT, 2.8 MT5, or 2.8 AT (156 hp).

Buy 3.0 AT only if you explicitly want Diesel and accept the slowest measured Coupe. 84 hp, 5 Inline, 163 Nm at 2400 rpm (the lowest torque peak rpm in the set), compression 21.5, 19.2 s, 150 km/h, 1550 / 2050 kg. Versus 2.8 MT5: −101 hp, +9.3 s, −50 km/h, +90 kg kerb. Fuel consumption is not measured, so Diesel economy is not a fact you can use here. Feed system for 3.0 AT is not measured.

Reliability / problems (what the data do and do not say). These launch data do not record failure rates, rust, or parts cost. What they do record as mechanical complexity differences: Carburetor vs Distributed injection (multi-point); 4 vs 5 vs 6 cylinders; Manual 4 / Manual 5 / Automatic 4; Gasoline vs Diesel. More cylinders and injection coincide with the highest specific output (67.4 hp/L on 2.8 MT5). The carburetor 2.3 AT (109 hp) has the lowest Gasoline specific output (47.2 hp/L) and the worst measured mixed Gasoline figure (13.7), except the carburetor six at 14. That is the reliability-adjacent fact in the sheet: the carburetor versions are not the economical ones on these consumption rows.

Short decision line. Want measured pace: 2.8 MT5 (or 2.8 MT 185 hp, 2746 cc). Want measured mpg: 2.3 MT5. Need Automatic: 2.3 AT (136 hp), not 2.3 AT (109 hp), unless you accept 13.9 s and 13.7 mixed. Need Diesel: 3.0 AT, knowing 0–100 19.2 s and mpg not measured. Do not pick a 2800 cc 2.8 AT / 2.8 MT / 2.8 MT4 expecting a proven gain — those performance cells are not measured.