How did diesel buses and taxis cope with short low speed journeys in London?

Diesel engines like to be driven hard and on long journeys at a good speed and RPM and diesels love motorways. But in the days when Routemaster buses and London taxis had Diesel engines how did the engines cope with the low speeds and regular stopping and starting in London traffic which rarely exceeds 20mph especially in central London? Surely the engines would soon get all gummed up with carbon. Was this a common problem with their engines requiring regular maintenance?

Diesels also run slowly in ships. They are probably designed for the environment they will run in. As for getting gummed up with carbon - have you ever seen a London bus moving away from a bus stop? They deposit the carbon on the car behind.

oops sorry dubble post.

As a footnote if you want to know if a decent current vehicle is any good look at what all the PHC guys are driving around in at the moment

If one domestic model dominates then it's a good buy that can be worked hard, I recall Nissan Bluebirds and Skoda Octavias ruling the Private hire world at one time

Edited By Ady1 on 27/03/2023 16:15:20

Specific vehicles like black taxis could sit at a rank all day with its engine ticking over

The TX1 in particular wasn't even run-in until 500,000 miles

it used a Nissan diesel

Ordinary domestic diesels were not designed for the abuse that business vehicles were expected to take

The trade off was mpg and performance

The TX2 with a ford engine and the Tx4 with a chrysler diesel were disasters for the trade, a lot of guys flogged off their TX2 and bought low mileage TX1s from London

The London guys didn't need to work their units so hard to make decent money, in the North and Scotland they got serious abuse

That’s a lot 500,000 miles. So I guess there is some truth that Diesel engines improve with mileage unlike petrols that wear down. I did once hear that older style Peugeot Diesel engines as well as the TX1 we’re almost indestructible, but is that just the engine block pistons and cylinders or the ancillaries too like the water pump, turbo, egr etc?

Edited By Simon Robinson 4 on 27/03/2023 16:27:22

It can depend on location.

I audited a ship client with a ford diesel running 24/7 for months which had been whipped out of a car and conscripted as the ships generator, It was under 2L, a 1600 or 1800 in the 1980s and had never conked out once

The relatively constant load probably made a big difference

The Ford taxi diesels were a disaster

Pardon? Mostly they still have.

I own an FX4/Fairway, the predecessor to the TX series cabs. It was one of the last built and has the 2.7 litre Nissan TD27 engine. Earlier FX4s had an Austin diesel, and after production of that engine ceased they used the Land Rover diesel, against the advice of Land Rover's engineers who felt that it would not stand up to taxi operating conditions. They were, apparently, correct.

The Nissan engine was much more robust than the Rover engine, with a 5 main bearing crankshaft and gear driven camshaft. It's more like a small lorry engine. The power output is quite low, about 80 bhp which aids durability. the automatic transmission has a feature which allows top (overdrive) gear to be locked out. The handbook recommends engaging the lock out for town driving - I don't know the reason for this, it might be to keep the engine revs higher and prevent cylinder bore glazing. I leave it disengaged all the time, but then I'm not a cab driver and my annual mileage is tiny by comparison.

it's not really true that diesels require to be driven at high speeds - one of the advantages of diesels is that they give good fuel economy at part throttle settings since the compression ratio (and hence thermal efficiency) isn't reduced by a throttle butterfly as in a petrol engine.

They also don't generally suffer from coking - diesels always run lean and with high combustion temperatures. The only seriously coked diesel I've seen was an old Perkins P6 which had evidently been used in some sort of road repairing tractor. The outside of the engine was thickly coated with tar and chippings, and the valve passages looked pretty similar, almost completely blocked with oily carbon - I can't remember whether it was just the inlets, the exhausts, or both that were affected. The combustion chambers were clear though. I presume it either had grievously worn injection components, or maybe had been used with some totally unsuitable (i.e. cheap) fuel.

It's the modern small diesels with Exhaust Gas Recirculation (EGR) and Diesel Particulate Filter emission control systems that need long runs to stop them clogging up.

Robert,

Edited By Robert Atkinson 2 on 27/03/2023 21:32:01

Proper taxis had an amazing turning circle which was great in town for low speed work but the suspension geometrics for town made driving over 55mph on open roads an extremely unrelaxing experience

Geared timing sounds good and is safer than cambelts and cam chains which can break. So what else makes the Nissan TD27 a good long lasting engine? Is it the durable engine block, cylinders and pistons? Do the ancillaries like the Turbo, EGR and fuel pump, electronics, engine management  etc also last a long time? I know in a lot of engines the EGR is quite troublesome getting coked up. But then I don’t know if there is a vehicle EGR that doesn’t need cleaning.

Edited By Simon Robinson 4 on 27/03/2023 20:16:20

They shouldn't be any problem to drive fast ("fast" being a relative term) if in good condition, but if the suspension is worn then they can indeed be unrelaxing. Even more so if you know that the lower wishbone balljoints are actually arranged upside down so that the load is taken on the neck side of the ball rather than its crown. This means that if severely worn they could simply pop apart allowing the spring pan and wishbone to slam into the ground and the hub carrier and wheel to flop loose...

I find myself getting caught out if I drive a normal car nowadays - the turning circle seems huge.

So what else makes the Nissan TD27 a good long lasting engine?

"It's Japanese" would be my answer

Almost everything they made back in the 1980s 1990s was awesome in its reliability and not that expensive

For a while it looked like they were going to take over the world, they could make standard stuff so reliable it was amazing

Edited By Ady1 on 27/03/2023 20:25:25

What is this EGR, electronics and engine management of which you speak? Some modern strangeness I believe!

These engines were all-mechanical - the only electronic gizmo was to control the cold start pre-heat, and the only emission control measure was positive crankcase ventilation. Some of the last Fairways were fitted with a turbocharger purely as an way of getting them through new (at the time) emissions regulations. I don't know if this was standard on the Nissan engined TX.

Part of the reason for their durability was probably down to the low power output - at 30 bhp/litre these were lazy, low stressed engines. This, at least until recently, was commonplace with commercial vehicle engines. The AEC AV590 9.6 litre used in the Routemaster only developed about 120 -130 bhp at 1800 rpm for example.

My Ford Granada had Puegot deisel in it, purred along nicely. but, the Ford agent where it was serviced kept messing with the slow running control. In fact they managed by adjustment to pull it out of its holder.

Also it ate exhausts, I must have welded it 20 times. It went to auction and yes, I got parking tickets from it. Which I did not pay.

Bazyle makes a good point. 100rpm might be tops for some marine engines.

The Lister CS pottered along for years at 650rpm max.

High speed diesel engines have not been around for so long? In the early 1960s(?) there was the Landrover engine - converted from the petrol version, which was never a “good” engine (4200rpm, I think).

Detergent oils becoming available virtually removed the gumming problem of previous engines (including diesel, petrol and distillate fuels). Again, wear was a factor of materials of the day and tolerance of parts. Things have moved on in recent decades.

My first diesel car (ignoring the Landy) left me at 125k miles with the engine in pristine condition - a peugeot 205. Our first 607 had covered 250k before being written off - the engine was still good. The second was scrapped at 195k due to other issues and the present one will fail its next MOT for body/chassis issues. None have needed oil between oil changes.

Smoke is more likely due to injection short-comings.

I am still driving a TD27 in my 1960 Series 2 SWB land rover. There's no turbo to give problems. The oil is changed every 5000 kms. The air filter accidently lasted 100,000 kms and gave me a noticeable jump in power when I replaced it and adjusted the injection pump to just below the dark smoke on steep hills point. The water pump regularly fails every couple of years and gets replaced by a copy pump as no genuine pumps are available in this country. The amazing thing is the fuel consumption at around 15 km/l or almost 40 mpg! I wish the land rover Series 3 gearbox I'm using was as reliable.

And at almost 100,000 miles I'm still on the same exhaust system as when I bought it second hand although it has needed welding up now and again.

Edited By Colin Whittaker on 28/03/2023 02:12:50

In the days before emissions controls, buses on stage carriage roiutes did put a lot of carbon into their oil

I can remember seeing a Leyland 0600 where when the rocker covers were removed after 300,000 miles, the head was solid with carbon, with slots where the rockers were operating.

Indirest injection engines, on stop/start work were even worse, and the oil would coagulate almost between services

Col;d running encourages sludge formation.

(Modern low emission engines do even when worked hard)

Howard

Edited By Howard Lewis on 28/03/2023 09:43:26

Many moons ago, I took a London black cab all the way home, instead of using the train as usual, (can't remember why but there was a good reason, and the company paid).......I lived 35 miles outside London, via roads much faster than the London streets. In the last couple of miles to my house, the cab's engine - unused to the vehicle running at speeds up to 60 mph, partially blew up! We got to my house and I often wondered if the guy made it back to London.

Regarding the longevity of some engines; I once spoke with a guy who used to work for Ford, and he said that domestic Ford engines are designed to last 3 years these days - the case hardening applied to valve-train components etc. is only good for that timeframe, he claimed. Judging by the rattling noise you hear from some Ford engines, he was probably right.

Diesel engines, certainly those in commercial vehicles, are designed for a much harder and longer life, so presumably have much better case hardening and higher quality steels etc in their engines?

"Lazy" lower power but larger capacity and torque engines do last longer than highly tuned, high power low capacity engines. I remember noting the honing marks still clearly visible in the bores of various Rover V8 engines I have rebuilt, at around the 90,000 mile mark; just nicely run-in !

In brief, London swapped small piles of horse manure for a more evenly spread layer of soot.

My car hates a prolonged sequence of low speed journeys, allowing it to rev high in first when pulling away every so often helps it keep its throat clear. Best not done with someone on your tail though.

Neil