Mercedes wins the crow'
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The 1625 S has less horsepower than the 1626, but Tim Blakemore has returned th( best fuel figures with it on our test route any 32-tonner with a van trailer; he believE operators will prefer this new model for several reasons
),SK THE DRIVER of a 1626 Mer:edes-Benz if he'd like it re)laced with a new 1625 and he'll ikely be as unsure of his reply as f you'd asked him, "Have you ;topped beating your wife?"
His train of thought would gobably go something like this: 'My old 1626 isn't bad. The cab s roomy and comfortable and )r) flattish motorway sections here aren't many units that will )ass me. But on the hills I've got o work quite hard with the welve speed gearbox even hough it is synchromesh, and ;till the likes of 250hp Cummins ind Rolls-Royce powered nachines overtake me. Now I :now that the last two digits in 11ercedes model numbers stand or the engine's horsepower so ghat I am being offered here is a ess powerful vehicle, and vhat's more I've heard that it )nly has an eight speed gear)ox. I'd certainly like a brand lew motor but this sounds to ne like a sideways promotion."
That in a nutshell is the mar(eting problem that faces Mer;edes-Benz with the 1625S, as a iirect result of its commendably vtraightforward model lumbering system. It is a conve-dent, and now commonplace, -iystem but it can lead to prejulice.
Those inclined to prejudge the 1625 should look at the results of :his road test first and they will Degin to see how relatively unimportant is the fact that the 1625's maximum horsepower is less than the 1626's. A comparison of the 1625 with the 1628, tested in CMJune 13 this year, is even more illuminating. The less powerful unit was a whisker faster over our 11 8 4.6km (736.8 miles) test route and used twelve gallons less fuel. Its 100.47 gallon consumption is less than any tractive unit so far has used in pulling our van semi-trailer around the Scottish route. The fuel economy crown that was firmly on the head of ER F's NT250 powered B Series is now being worn by the Mercedes Benz 1625.
The derated engine The OM 422 111 engine used in the 1625 is a derated version of the 1628's OM 422 1, both being larger capacity versions of the OM 402 that was in the 1626. Along with numerous other changes, the bore has been increased by 3mm (0.118 in) and the stroke lengthened by 12mm (0.4721n). You would need to be eagle-eyed to spot the only visible external difference between the two new engines (apart from their identification plates) which is that the more powerful version has taller delivery valves on its Bosch in line injection pump.
However, there are some interesting noticeable differences in the engines' specific fuel consumption curves which account in part for the better on-the-road fuel economy of the derated version. Both reach their minimum specific fuel consumption at 1 20Orpm-maximum torque speed, but the OM 422 111's curve is lower than the fully rated engine's. It reaches a markably low minimum of g/kWh (0.3251b/bhp h) an stays very close to that fig right down to 800rpm.
At this speed the 276bhp's gine's sfc curve has ri: sharply. In practice such a engine speed isn't used either the 1628 or 1625 but driver follows the rnanufac er's recommendation he wil the engine work at 1100 1200rpm before changing dc a gear. In situations like that 1625 will always be using I than its more powerful ther.
iver the 40mph sections of route, the engine was alway 'king at a speed of 1400rpm ass. It was here that the 1625 exceptionally well on fuel nomy, returning 8.27 mpg on Gretna to Hamilton section 8.44mpg on the Neville's ss to Darrington section.
here are four versions of the 422 engine in production. two that have not yet been oduced to Britain are the turharged 243kW (330bhp) OM A and the turbocharged and rge cooled 276 kW(375 bhp) 422LA. Neither of these has iinimum specific fuel coniption as low as the OM 422 learbox
esn't the 1625 need a twelve )cl gearbox like the 1626?" is :her question the established i driver might ask. After this a day test the answer is an hatic "No-. The 13:1 deep fler ratio of the ZF 5S-92GP ;hed with the standard rear ratio of 4.205:1 gives the , a restart gradeability of 1 in ie remaining eight forward s are well spaced to match ,ngine's characteristics.
,er just about the toughest section of A road in the [try, the A68, the lowest I needed was the 5.90: 1 of )nd (third if you count ler as first). And at the other Df the ratio spread, top gear :1) with this differential gives the 1625 an actual mum speed on the flat with mgine pulling at 2200rpm, 15 km/h (65mph). So at the maximum of 60mph the
tachometer needle is just outside the green "economy" zone at 2100rpm.
The two intermediate gears that were used most during the test were second and seventh. On this S92 gearbox there is less of a gap between seventh and eighth than there used to be on the old S90 box, and that makes seventh a very useful gear indeed. I found that the best policy was to change down from eighth at about 1400rpm and then I could depend upon seventh to take us over most motorway gradients. The northbound carriageway over Shap, for example, was climbed in seventh at a steady 40mph.
The 1625's carefully chosen gearing disguises the engine's relatively low torque rating — a maximum of 932 Nm (687Ib ft). Now this is more than the 1626's lowly maximum of 814 Nm (600lb ft) and even more significantly the torque rise on this engine has been improved to 23 per cent. But still by comparison with many competitiors the OM 422 111's maximum torque is modest.
My impression of the 1628, rated at 1040 Nm (765Ib ft) was that it needed 50 or so lb ft extra to make it more driveable, so it was logical to assume that the 1625 would leave a similar, even stronger, impression. On the contrary, any doubts I had about the 1625's driveability were completely dispelled on the first day of the test at the end of which I noted that if the door badges were taken off, most drivers would have difficulty in deciding which of our test vehicles, the 1625 or 1628, had the more powerful engine. It would be interesting to see what effect would be made on the 1628's performance by fitting a direct top gearbox and the same rear axle ratio as used in this 1625.
Double H change Like all Mercedes with range change ZF gearboxes, the 1625 has the "double H" system for changing from high to low range and vice versa. At first this is a little difficult to get used to, the tendency being to use too much force to flick the gear lever across the gate, but with practice rapid changes soon become easy.
One improvement I would like to see made to the systerr concerns the dashboarc mounted "Hi Lo" warning lights These are really useful because they confirm at a glance which range has been selected.
The trouble is that they are wired into the rheostat which dims all the panel lights auto. matically when the sidelights are switched on. This in itself is also an excellent idea, preventing a driver from being dazzled at night by too bright warning lights, but in daylight when the range change lights are dimmed they become invisible. So all the advantages of the warning lights are lost when the side or headlights are switched on in foggy or wet weather.
The "M" cabbed 38-tonner Mercedes-Benz is unique in offering three cab lengths for the British market: the "S" (short day cab), the "M" medium (short sleeper cab) and the "L" (Long sleeper cab). The 1625 is aimed at domestic rather than international hauliers and only the shortest two of these are offered on one wheelbase chassis — 3.0m.
It seems to me that the only major disadvantage of the sleeper cab version is its price which is £1,060 more than the "S" cabbed machine.
The weight penalty is small at only 210kg (951b). This sleeper cab is attractively light with a ready for the road kerb weight, including fifth wheel installation, all normal in-cab equipment and a full 3001it (66ga1) tank of fuel of 6350kg (6 tons 5 cwt). This left capacity on our van semi-trailer for a payload of well over 201/2 tons.
Moreover, without resorting to outlandish king pin positions or heart stopping, wafer thin swing clearances the sleeper cab 1625 can couple to a 12.2m (40ft) semi-trailer without exceeding the 15m legal maximum overall length.
A number of recent cab modifications, including in Mercedes-Benz terminology "the 1A execution", were included on our test vehicle. The park brake lever has been moved from the engine hump to the offside of the dashboard; there is no longer an hydraulic link to the air brakes, the brake valve is now fitted in the cab immediately behind the steering column; the radiator header tank has been moved from the rear to the front of the cab; the windscreen washers are controlled by a column mounted switch instead of the old vulnerable, floor mounted one; there are additional grab handles; and noise insulation material has been increased in thickness to 80mm.
All of these seem to me to be worthwhile improvements except for the repositioning of the park brake lever. In its old position it might have restricted a driver's left leg movement somewhat but at least it was easy to reach without stretching forward and there was no danger as there is now of the brake being accidentally released when the driver enters or leaves the cab.
There is no sign yet of the heater controls being moved to a less eccentric position though as I reported in the 1628 test, Daimler-Benz has promised a change for UK specification vehicles before the end of this year.
Suspension well sorted This test provided a good oppurtunity to compare the ride and handling of this 3.0m wheelbase unit with the longer wheel'base 1628 which was tested earlier this year.
The state of repair of the roads over much of our route is so bad that it provides a comprehensive test of any vehicles suspension. Like the 1628, the 1625 came through with flying colours and confirmed my original impressed that MB's cab and chassis suspension package, even without suspension seat (optional on the 1625) is well sorted. Inevitably, the shorter wheelbase unit did not have quite such a super smooth ride as the 1628 but there was no unpleasant pitching or rolling.
Like it's compatriot, the MAN 16.240 FTN, this Mercedes had a park brake performance that was barely adequate. Operating on the drive axle only, the brake just managed to hold the fully laden combination on a 1 in 6 test hill. Mercedes has never been renowned for spectacularly efficient park brakes ever since the days of the multi-pull device on the old 1418's /1924' s am time they were improved. can operating engineers t pected to maintain brakes the C and U standard wl brand new vehicle only complies with it?
Summary Where the 1628's perforn over our test route was diocre only, the 1625 we: standing, setting a new fue sumption record, and not expense of average speec less powerful Mercedes I: much more of a drix machine with gearing perfectly matches the ch engine's characteristics. It i ticlarly well suited, as our r show, to light load, A-roac ning but even when the gets tough it is a 32/38 t that will take some beating