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I've always considered an engine to be labouring if it's making loud banging and clattering noises (eg 25mph in 5th), otherwise it's fine. I've thrashed my diesel for the last 40,000 miles but with 6000 mile oil changes and time for the turbo to simmer, and if anything it feels faster and freer than ever.
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What do you call thrashed, i would be interested to know.
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As per OldHand's tips but I'd beware of flooring it from really low revs - you won't strain the engine but doing it regulalry will put a big, big strain on the clutch (many dual mass flywheel problems with cars producing big torque figures). Then I'd just look after it by running it on high quality fuel and change the oil every 5,000 miles but many here will tell you, probably rightly so that you don't have to.
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e must ask ourselfs why we impose rev limiters on engines and what the limiting characterisics of diesel and petrol engines are.
In petrol engines I have heard that valve springs are mostly the limiting factor if you go well beyond the rev limiter.
In diesel engines I have heard the pistons and assciated items are heavier than they are in petrol engines, this can limit the rev limits.
If you produce a lot of heat in the engine (read the engine is burning a lot of fuel effiecently, and hence producing a lot of power) the diffrent parts of the engine change size, so presumably making the engine burn more oil and damage the seal of the combustion chamber. This implies that using the max power of an engine for a few seconds does not damage it, since temperature differentails and absolutes will not exceed damageing values. Using an engine at close to maxiumum power (prehapps in prolonged high speed crusing?) will therefore be much more damaging to an engine. That is for every minute of prolonged high power usage you will do more damage cruising, rather than taking the engine up to the red line, flooring it.
We have to take into account the nature of combustion of diesel and petrol. Factors such as the diffrence in swirl rates in the combustion chamber between petrol and diesel are prehapps key. In diesels an upper rev limit is imposed by how it combusts in the cylinder and the nature of that cumbustion. In the same way a petrol engine has a self imposed rev limit (is this what explains why torque curves first go up and then down as engine speed increases?). This is also why engines with 4 valves per cylinder produce more torque and therefore power higher up the the rev band compaired with engines with 2 valves per cylinder (it is all to do with how the engine breaths).
To OldHand the diffrent nature of how diesel and petrol engines breath may explain why diesel engines labour at lower revs than petrol engines, but I am confused at the machincial damage produced when you labour an engine. I have heard that labouring an engine is not only bad for fuel consumption, but for the actural engine (IIRC its something to do with bearings not being up to the job?).
To NeilS, if you are concerned about how engine torque strains the clutch would it not make more sense not to 'floor it' at revs where the engine could produce its maximum torque figures. clutches feel most strain when changing gear. In gear you don't need to bother about torque figures and certainly not at very low revs. In petrol cars max. torque is about 4000RPM and in Diesels 1750-4000 rpm, therefore 'flooring' a car at low revs would not be any more damaging that 'flooring' it at 40000 rpm. I do agree that when changing gears low revs (or at least matching the revs of the engine and the clutch) is best.
My advice to the OP is to buy the most powerfull engine you can since you will be putting it under less stress whatever driving you do, which can't be a bad thing. The second bit of advice is that the OP should look carefully at the fuel system of the diesel they wish to buy. If you are going for a CR type diesel I should imagine the trade off in diffrent CR systems, versus the reliablitiy of petrol maybe a better question, rather than asking how an engines maxinumum power/rev charactistic affects its lifetime reliablity.
Sorry for long post. If I have got the wrong end of the stick I would be gratefully educated, but the thread seemed to deal with all the issues in my post.
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Torque means nothing without RPM
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very easy to blow (stress ) a weasel just labour it in a gear or thrash the life out of it
i have 3 diesel vehicles but use them as work tools only ,i never stress them
i use petrols if i want to get a move on
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I haven't had time to read the whole of this thread. Having been in the diesel business for most of my working life, I'll give my recommendations for a long and trouble-free engine life. Take the opposites to these and you will stress the engine in some way or other and shorten its life.
Change oil and filter frequently using OE filters and adhering absolutely strictly to the manufacturer's oil specification for the duty the engine is operating under.
Treat the engine as if it were brand new until it is hot - by which I mean the oil is hot. The oil takes about 3 times as long to heat as does the water jacket at normal ambient temperatures.
Do not labour the engine - ever.
Do not rev the engine off load - I hate the MOT smoke test.
Idle a hard-worked engine for 1 minute before switching off.
Maintain the fuel system carefully, use OE filters and drain the water trap every service - one day you will be glad you did.
Investigate problems promptly and don't expect any diesel to start with a deficient battery. A minimum cranking speed is necessary to ensure that the heat required to initiate combustion is supplied at a higher rate than it is dissipated in the cold metal. Use Beru glowplugs.
My final point is perhaps the most contraversial but is based on experience: Buy an engine with a Bosch fuel system.
659.
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I would suggest that labouring a diesel engine will manifest itself in problems elsewhere first. Namely, clutches and flywheels as these are genuine wear and tear items whereas bearings and shafts will last a lot longer before labour-abuse catches up with them.
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I was brought up to never run a turbo-diesel at less than 35% power for lengthy periods, and for naturally-aspirated units, 25%. It is to do with the combustion efficiency. Remember that, in terms of air/fuel ratio, diesel engines are essentially constant air variable fuel if naturally aspirated, or below turbo useful output in T/C units. War - story - I once had to keep a 600 hp turbo-charged Cat diesel idling [ for safety reasons ] for some 8 hours. It took some 2 hours to burn off all the deposited soot and get a clear exhaust again once I could wind it up to near full power. Personally, I don't like diesels where they would be subjected, as a matter of course, to long traffic jams or similar because of the effect of poor combustion. In my experience, admittedly more on marine installations, the bottom end running causes more problems that hard running.
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I would suggest that labouring a diesel engine will manifest itself in problems elsewhere first. Namely, clutches and flywheels as these are genuine wear and tear items whereas bearings and shafts will last a lot longer before labour-abuse catches up with them.
how will the clutch and flywhel labour if you are labouring the engine? (are you thinking dmf?)
bearings and shafts will take the full brunt of any labouring and will indeed try to make a legg out for it
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My final point is perhaps the most contraversial but is based on experience: Buy an engine with a Bosch fuel system.
Agree with this apart from this one!
Bosch systems are just as carp as the rest, I sponsored Bosch for a new HP pump on my Alfa & both Alfa & Bosch struggled to diagnose it as well!
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I see lots of diesels, most considerably larger than car engines. My final point was a generality but based on many engine observations. It's a while since I've looked at a Fiat/Alfa small diesel, but some questionable applications engineering sticks in the back of my mind.
It might be worth trying to find out the cause of the HP pump failure - these things are intrinsically simpler than injection pumps (no governor for instance) but are of course similarly prone to dirt/water damage. Check the external causes first.
659.
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I'm sure there was a reasonably modern turbodiesel from a major manufacturer that could suffer big end failure if repeatedly asked to lug from low revs in a high gear. Something to do with the oil pressure being insufficient at these low crank speeds to stop the oil being squeezed out of the big end bearings under the huge torque generated by the piston. If this occurred regularly, the bearing would eventually fail.
I cannot for the life of me remember who it was, and where I read it.
Cheers
DP
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The motor geek in me is fascinated! Interesting when you realise that no matter how much 'they' want cars/engines to be 'white goods', there's a lot more to it than that...
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This implies that using the max power of an engine for a few seconds does not damage it, since temperature differentails and absolutes will not exceed damageing values. Using an engine at close to maxiumum power (prehapps in prolonged high speed crusing?) will therefore be much more damaging to an engine. That is for every minute of prolonged high power usage you will do more damage cruising, rather than taking the engine up to the red line, flooring it.
I was told that flooring it will deplete the oil cushion between the bearing and shaft. I suppose if you were to accelerate like you would normally and then just keep going, that would be the best way.
Can't see high speed cruising being bad as the engine is loaded so is worknig as intended, just very fast.
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At low revs, the bmep is somewhat lower than at maximum torque, and output is governed by the ECU, therefore the forces at the big end will be lower. The oil pump is designed to provide the same pressure at 800rpm as at 4,000rpm. I can't see that the crankshaft bearings are vulnerable at designed speeds unless there is a shortage of oil. Where the engine could be vulnerable is a) full power whilst cold - lack of oil b) missing a gear and overrevving. c) low oil level due to "white goods" mentality. The latter is more prevalent, affecting at least 50% of the driving population. Present company excepted.
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I'll try to take these points in order:
Although the BMEP is lower than the max torque value at low engine speeds, its absolute value will be much greater (probably twice) that for an equivalent petrol engine of similar size and hence similar bearing areas. This therefore represents a hazardous area of engine operation. If the driver demands max fuel at low revs, the engine will get it when the boost pressure develops, otherwise the ECU will not be exploiting the engine's output capability. The max fuel value is almost always smoke-defined unless some other engine parameter (eg excess speed) causes the ECU to limit this in order to ensure engine safety.
In the real world of a well used hot engine, using oil at the end of its service interval, I have yet to see an engine with the same oil pressure at 800 rpm as at 4,000. This would require overdesign to an extent I have not seen, even on military engines. Because low oil pressure occurs under labouring conditions the danger of operating in this area are compounded.
Full power when cold. Very damaging, clearances not established, poor oil flow, non activation of temperature dependant oil anti-scuff additives etc. etc. Don't do it.
On any diesel, the governor will ensure safety in the event of max speed being approached. That's what it's there for - but unless you're the MOT man, don't use it.
Low oil - all big engines and many car engines such as my VAG unit now have oil level warning. Any engine will be damaged by low oil levels, especially when combined with other factors such as high outputs, high ambient temperatures or angles of inclination near the limit.
659.
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659
Who makes the VAG PD fuel system and what is your opinion on that system ?
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Robert Bosch.
The PD (unit injector) system is the most efficient way of fuelling a diesel and will allow injection pressures which are higher than those of any other system. It is commonplace in large commercial diesels and will run for hundreds of hours without attention and within calibration.
The downside of the system is the forces which have to be generated within the engine via the camshaft drive in order to achieve these pressures within a short time interval. This is no problem on a big diesel - the camshaft(s) are gear driven with gears the size of teaplates, but the poor little VAG unit has to make do with a belt. It's damned marginal.
As an example, when the "PD" injector fires, the belt stretches and VAG machine wider teeth slots at the critical points on the crankshaft toothed wheel (4 on a 4 cyl engine) to accomodate this. The stresses on the camshaft are considerable and the wide roller-follower cam for the injector leaves little room for the valve cams, which are very narrow.
All of this is evident on examination of the servicing requirements - belt change every 4 years (mileages have come down recently in the light of failures) and a need for special oil to ensure camshaft survival.
The PD is not the most refined of diesels as pilot injection is difficult (but not impossible) to arrange with this system, but it's extremely efficient. It will meet its maker's claims for economy in general use - not all others do. The injectors and electronics are trouble free - the MAF sensor is about the only weakness not caused by abuse. It's easy to replace and fairly cheap.
I'm very pleased with mine - but beware the Euro Cat IV versions as particulate filter blocking has been reported. If you address the weaknesses, the engine will give good and efficient service.
659.
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I'm very pleased with mine - but beware the Euro Cat IV versions as particulate filter blocking has been reported. If you address the weaknesses, the engine will give good and efficient service.
Not all Cat IV VaG PD engines have a particulate filter, my Audi 2.0 TDI 140 does not however the 2.0 TDi 170 does.
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I do agree that a diesel engine will probably produce twice as much torque as a petrol at very low revs, but twice very little is still nothing much! As for 800 rpm oil pressure - I concede i may be wrong. But I'm not really sure that there is a significant problem from this aspect - overshadowed by negligence in oil replenishment. I realise that you have seen a number of cam-related failures on PD engines. How many bottom end repairs needed on diesel car engines?
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Bottom end failures are indeed fairly rare on diesel engines as they are generally nowadays - usually the effects of neglect will show sooner in other areas. This is probably as much a tribute to modern lubricants and bearing materials as to anything else.
Starting assistance with volatile liquids from spray cans directed into the intake is a fairly good way of dispatching bottom end bearings if you choose to use this as a substitute for proper maintenance.
659.
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I was under the understanding that part of the reason that diesel engines lasted longer than their petrol counterparts (generally speaking) is because (again, generally speaking) they're put under less stress by the drivers. You don't tend to really thrash a diesel engine as the OP suggested, especially when compared to say, VVTi/VTEC engines...
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people who drive ,but dont own, tend to stress diesels most.
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people who drive ,but dont own, tend to stress diesels most.
Definitely!
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