Diesel engines (Q1) "Designed to be driven hard"

Are you confusing this with an Italian tune-up?

You can get problems with Diesel engines if you only do short trips.

An "Italian tune-up" is a driving technique for diesel engines, involving sustained high RPMs and load to burn off carbon deposits, clear fuel injectors, and force Diesel Particulate Filter (DPF) regeneration. It works by increasing engine temperature, airflow, and exhaust velocity to remove soot and gunk that can accumulate from frequent short trips and city driving. To perform one, warm up the engine, find a safe area, and drive for a sustained period (e.g., 15 minutes) at high, but not necessarily redline, RPMs to clean the engine and help prevent clogging.

I was told it is good practice even for a petrol engine to drive at high speed - or low gear - for 20 minutes each week. Any truth?

Possibly just taking the car for a run that gets it up to full temperature and keeps it there for 15/30 minutes is all that is required, especially in winter.

Indeed! A necessary pre-MOT job for our 2009 diesel Fiesta (shopping trolley) and VW Passat. A couple of trips involving motorways suffice.>

It is a two-stroke diesel and getting on for 70 years old. It's not going to be clean in any sense of the word.

They never were clean. Normally aspirated diesel canonly get more power by throwing in more fuel.

Although the Deltics were supercharged, the same still applied, juts at higher power levels

I notice that they leave the engine running whilst they do all the other MOT checks before they check the emissions. Somewhat defeats the purpose of my 10 mile, round the block, journey to get the engine warm when the garage is only 2 miles away.

My local MOT warns

"Owners of diesel vehicles should be aware that the exhaust emissions test can put severe strain on the timing/cam belt (if your vehicle has one). Should this belt snap during the emissions test, catastrophic engine damage will most likely occur. If you are unsure about the integrity of you timing/cam belt, please talk to us when presenting your car for it's MOT test!"

Ive had tow cam belts snap on me. Both Vauxhalls - a Nova and an Astra. In both cases the engine was at idle and the car was stopped and the belt snapped on pulling away at very low revs. In both cases the only collateral damage was snapped rockers.

I had a petrol Nova cam belt snap on me on the forecourt of a petrol station seconds after pulling away from the pump. I was lucky and only the belt had to be replaced.

The other problems I had with Nova were electrical, usually connectors and connections to components/switches etc. The plastic they used for the shell of the connectors was too soft. When mating a spade type connector instead of mating securely the spade would push the mating part out of the back of the plastic shell so only a very small bit of the spade was making a electrical connection. A bit of vibration and the connection would let go.

I suppose petrol-engined cars are less affected by a cambelt snapping. Diesel engines, with the greater compression ratio, often have the piston going much closer to the valves - so-called "interference engines" - and the piston and the valves overlap, though never at the same time, so it's only the cambelt which prevents them colliding.

My old boss had a Rover SD1 and he kept a badly-mangled piston on his desk. It was a petrol engine, but an interference design. The cambelt snapped and the piston collided with the valve because without the cambelt the valves didn't move out of the way so either the inlet or the exhaust valve punched a hole in the piston. That was an expensive repair

- I can't remember whether it needed a new engine or just a new piston, valve and cambelt.

My car is a Peugeot with a 1.6 HDi engine, and I was warned to get the cambelt changed well within the stated replacement time. I've had it done once and at some point it will be due its second replacement since the car's now done 200,000 miles. That will be a nice "little" repair job. Last time I was advised to get the water pump changed at the same time as the cambelt, since the pump is driven by the cambelt, as a precaution: it's cheaper to replace a water pump even if it's not needed, than to pay all over again for the labour. I wonder why cars started using water pumps that are driven off the cambelt, rather than driving them off the "fan belt" which drives the alternator (and the fan, in the days of non-electric fans). I remember my grandpa proudly showing me the running repair that he'd made using my grandma's tights when the fanbelt on his Hillman Avenger snapped. You can live without an alternator for a short distance to get you home (*), but the engine will overheat without a water pump. Maybe that's why modern cars don't drive it off the auxiliary belt - maybe that belt is more likely to fail than a cambelt.

(*) My auxiliary belt failed one night when I was in Lane 3 of the M40. I heard a strange twang and the ignition light came, which is fairly indicative. And as soon as I tried to change lanes, the steering was very heavy. As it happens, I was just a mile from the junction where I was planning to come off anyway, so I turned off as normal - a bit hard to steer round the roundabout and turn off onto the A34, but I knew there was a petrol station a mile head where I could wait for the RAC man. I was toying with the idea of continuing home, but I decided 20 miles was pushing things a bit for the battery with the headlights on.

You can not extrapolate on the effects of cam belt failures. Some cars, e.g. the MX-5 have non-interference engines, so the valves and pistons will not collide on a cam belt failure...

Dave

Indeed no, but my original point was that cam belts just fail for no apparent reason whatsoever....hard driving not being necessary

And sometimes it seems quite difficult to be completely sure whether a given engine is interference or not (other than waiting for the belt to break!), I've never seen it in a manufacturer's spec, just hearsay.

nib

Nope!

And petrol engines!

Well, of course!

Apparently the important bit is to not let the engine lug. Puts undue stresses on things from what I've been told, especially at cold temperatures.

The important thing for engine longevity is to get it to operating temp ASAP (and keep it there).

(This is "just wot I've 'eard, gov." so don't go believing me.)

Probably especially true of engines with dual mass flywheels. Great for smoothing out vibrations at low revs but only by absorbing the low frequency impulses.

Tim

It is a scavenge pump rather than a supercharger, the power of a deltic was more to do with it being a two stroke.

It suffered the same problem of other uniflow engines in that it lost lubricant to the combustion chamber.

The same was true of the high powered piston engines developed for fighter aircraft toward the end of the war, sleeve valves lost lubricant to the compustion nchamber.

That's why plain old 4 cylinder engines became the norm, good sealing with poppet valves and rings/scrapers to keep extraneous oil under the pistons.