fuel consumption -- my M189 guzzler

[OzBenzHead]

The MBCQ Concours d'Elegance was the first time I had ventured so far from home in my 300SE coupé in my five years of custodianship.

I seem to have finally sorted the fuel blockage issues (rust in tank - ) and have not had a starvation in more than 900 km. (I've only just clocked up 1000 miles / 1600 km in five years.) The next stage will be to lean out the mixture, as he's running very rich -- thick black soot inside tailpipe, and a blast of unburned fuel when gunning it up a good hill overtake in third.

The trip also was the best test of thirst to date; a February run of 90 km each way was roughly calculated then, but I wasn't too diligent with accurate fills.

For the Brisbane trip:

• Load: Driver (75 kg incl clobber); large toolbox; two spare wheels; 2.5 tonne capacity trolley jack; spare vital fluids -- water, coolant, oil, ATF, brake; car cover; H/D battery jumper pack; overnight bag.
• Tyres: 205 70 14 inflated cold to 38 psi
• Highway north (225 km): 14.7 litres / 100 km (average speed 114 km/h) -- very early morning / dawn, no traffic; Saturday
• Greater Brisbane -- north, south, east/bay (112 km): 19.6 litres / 100 km (yoiks!) Sat / Sun / Mon
• Highway south (268 km): 15.34 litres / 100 km (average speed 110 km/h) -- early afternoon Bris. departure, moderate traffic; Monday.

According to the factory specs, one should expect fuel consumption in the range 11-18 litres / 100. (My city driving was thirstier than that, though I was driving / braking on the auto box all the time, having experienced a complete brake hydraulics failure on arrival in Brisbane -- that possibly upped the thirst a tad, as it meant lots of intermediate gear work / higher revs; I already had no handbrake connected -- something I'd forgotten about before the trip -- doh!).

Given the factory figures, the age of the car (44), its complexity (compared with most other Benzes), its weight, the trip load, and its easy performance over the trip at a suitably rapid yet relaxed pace, I'm content enough with those highway consumption numbers.

Of course, a better test could be done using GPS, but I relied solely on the odometer and tripmeter (and a stopwatch) and closely observed maximum top-ups. I must check my speedo for accuracy against a GPS, as I've no idea how its gearing relates to the current tyres -- let alone how tired it or its drive might be.

 

[Styria]

Ah, that M189 engine - what a magnificent, monstrous thing to look at - and what an expensive thing it is to recondition but, but, what a wonderful engine. It was stolen from the Gullwing, and gradually refined, being of all alloy construction in the end.

Part combustion chamber in the piston crowns, slanted block which, in configuration at least, was similar to the overhead inlet, side exhaust valve Rover engine of the forties to the sixties.. In the end, Mercedes managed to squeeze about 195 bhp from the engine, but it was discontinued in 1967, considered to be too old, too slow and too expensive to manufacture and the latest 300SEL with a six cylinder unit was the M130 2.8 litre engine - supposedly more powerful than the 300 unit, certainly cheaper to manufacture, but the model only lasted for one year. Very rare, but Damo, one of our 'topklasse' members has just such a model, with a manual five speed gearbox.

Your fuel consumption, Gordon, is probably all you can expect. With my 300SE that I owned in the seventies, 17 mpg on a trip was about what one could expect. I recall towing a box trailer with bike on top to the North Coast, and we also took a Rover 3500S at the same time. We'd normally stop at Taree to stretch legs and bowels, and to replenish the petrol tank. I clearly remember, the Rover cost $9.00 to refill, the Mercedes $18.00. Given that the Rover was capable of 25 mpg, that meant that the 300 returned 12.5 mpg.

Gordon, I wouldn't mind a couple of pics of the engine, so that others can appreciate what we're talking about. BTW, one thing I hated about that engine was the location of the water pump and alternator at the side of the block, and THAT water pipe from pump to Inlet manifold - removal of that component - what a monster of a job ! Regards Styria

 

[OzBenzHead]

Ah, that M189 engine [...]

Your fuel consumption, Gordon, is probably all you can expect. With my 300SE that I owned in the seventies, 17 mpg on a trip was about what one could expect. [...]

Oh, I wasn't complaining at all -- I was quite happy to get those highway figures. As it's not used as a town car / runabout, I don't care about the city cycle thirst. If you got 17 mpg on a trip in your 300, then my 19 mpg (approx.) on the up trip was most satisfactory.

Gordon, I wouldn't mind a couple of pics of the engine, so that others can appreciate what we're talking about. BTW, one thing I hated about that engine was the location of the water pump and alternator at the side of the block, and THAT water pipe from pump to Inlet manifold - removal of that component - what a monster of a job ! Regards Styria

In no particular order ...







Water pump is attached to rear of this ginormous genny.

 

[WGB]

That mileage doesn't sound too bad to me for a car of that era.

Beautiful engineering visible in those photos.

Bill

 

[John S]

If you can smell raw fuel and the tail pipe is blacker than normal for the era, expect 1 or 2 litres per 100 k's less once it's fully tuned and the timing is spot on.

 

[OzBenzHead]

If you can smell raw fuel and the tail pipe is blacker than normal for the era, expect 1 or 2 litres per 100 k's less once it's fully tuned and the timing is spot on.

I suspect some of the soot in the tailpipe is a by-product of unleaded fuel, but that doesn't account for the toxic cloud of unburned vapours from the tail when fanging it in third.

Of course, too much fanging it in third will see me using 20 litres / 100 km!

It was pleasantly surprising, too, to discover that the oil level neither dropped nor rose, there was no water loss, oil and water remained clean and separate ... so my conclusion is that the engine must be quite sound.

And for torque it leaves all my other -- including newer -- Benz sixes for dead. Go the last of the long-strokers!

 

[John S]

Ah yes, back in the good old days when torque was as important as power and you didn't need a zillion revs to move along smartly. 195 BHP @ 5,900 rpm and torque of 195.3 ft pd @4,700 rpm.- a bit high in the rev range but spread over a wide band.