Mercedes Diesel Engines - why so many problems?

[jberks]

For mileage covered I don't think there are many problems. Yes you hear of issues but more often than not, the car in question has already performed faultlessly for 140,000 miles plus, so it's entitled to a bit of a weakness.
Mine is now up to 88,000 miles and has never missed a beat. The engine is sweet and no signs of wear. I fully expect another 80,000 miles without concern. Ok, I have replaced the odd sensor and pipe but I had similar faults on my old unstressed E240 so its not a diesel thing. Actually I had issues on my 240 that I wont see on my cdi (ignition related) and that was gone by 75,000 miles. This evening I will jump in, flick they key, the lights will come on as will the wipers, the aircon will heat and dehumidify as always and she will cruise the 50 miles home as effortlessly as she did on the way here, sitting happily at 50-80 and if I ask for a quick spurt to 100 it will happen instantaneously and at a rate few petrol cars could keep up with. I filled up on Sunday and the trip meter will read over 600 miles before I need to go back.
I don't think, unless I could afford to run a V8, I'd go back to petrol and even then, it would be a hard decision whether to have a thirsty 500 or a chipped 320cdi.

Modern cdis are used primarily for high mileages. Think of a modern taxi or rep mobile and it's obvious that reliability issues wouldn't be tolerated for long. But at the same time, with high fuel pressures, turbos and emmission issues, they are more complex and more stressed than their petrol equivalents, in which context their true reliability is actually very impressive.

 

[jachin]

tpo and bottom of the problems is that they try to make things overly complicated. take the general set up on my E300 TD. fuel comes from the tank, to a fuel heater, then to a pre filter, then down to the lift pump then up to the fuel filter, then down to the shut off valve then to the injector pump, then fuel can go via a return to the tank or from the filter to the tank if required. whats wrong with fuel going from the tank to the lift pump to the heater, to the fuel filter then the injector pump with the cut off solenoid built in? the return goes from injector pump/leak off rail straight to the tank, no connections (in most cases to) the fuel filter (like ford, vauxhall and most other manufacturers use) and why cant normal jubilee clipped hose joints be used instead of stupid push fit plastic unions with rubber o rings? i know they have got more complicated for emissions sake, but why couldnt the basic set up have been kept simple?

I agree as Pete knows I just got 140k out of my gloplugs and 2 just died, my advice; get a very late 124 300D and change the oil es 5/6k miles whatever the book says!

 

[Number_Cruncher]

>>fuel comes from the tank, to a fuel heater, then to a pre filter, then down to the lift pump then up to the fuel filter, then down to the shut off valve then to the injector pump, then fuel can go via a return to the tank or from the filter to the tank if required.

It goes to the fuel heater first to avoid waxing - this could interfere with the valves on the lift pump, and could jam up any of the filtering which happens downstream of here.

It goes to the pre-filter, again to prevent larger particles either wearing the valves in the lift pump, or jamming them open - the car would come to a stop. This is because the car has quite an old fashioned piston and valve lift pump as opposed to the rotary vane lift/transfer pumps found on distributor type injector pumps. Some older designs still of lift pumps had the mesh pre-filter built in under a glass dome.

The fuel up to the lift pump is only being propelled by atmospheric pressure, so, you can't pass it through a fine filter - therefore, the secondary filter comes after the lift pump.

Having the cross drilling in the filter head allows the system to self bleed - without it, the system would need bleed valves and a primer pump.

Systems where the main fuel filter is on the suction side do not circulate as much fuel as our systems do - our systems are less prone to waxing, as the fuel in the tank will tend to stay hotter.

The fittings are horrid, but are cheaper at assembly time, as they simply snap into place. It doesn't help us who have to run them years down the line....

 

[steve--o]

ive just bought an 87 124 250 td lhd with 310k on the clock,water pumps shot,probably idler pulley and alternator bearings to do us well,but no rot,startes & drives nice,no smokes,clunks,rattles
slight tappet ,ie rattle that i can live with,but might have a go at sorting later.
wonderfull old car

steve in a 3 deg Almeria with log burner on and a tin of 5.2 % 19p beer in hand ! :lol:

 

[turbopete]

>>fuel comes from the tank, to a fuel heater, then to a pre filter, then down to the lift pump then up to the fuel filter, then down to the shut off valve then to the injector pump, then fuel can go via a return to the tank or from the filter to the tank if required.

It goes to the fuel heater first to avoid waxing - this could interfere with the valves on the lift pump, and could jam up any of the filtering which happens downstream of here.

It goes to the pre-filter, again to prevent larger particles either wearing the valves in the lift pump, or jamming them open - the car would come to a stop. This is because the car has quite an old fashioned piston and valve lift pump as opposed to the rotary vane lift/transfer pumps found on distributor type injector pumps. Some older designs still of lift pumps had the mesh pre-filter built in under a glass dome.

The fuel up to the lift pump is only being propelled by atmospheric pressure, so, you can't pass it through a fine filter - therefore, the secondary filter comes after the lift pump.

Having the cross drilling in the filter head allows the system to self bleed - without it, the system would need bleed valves and a primer pump.

Systems where the main fuel filter is on the suction side do not circulate as much fuel as our systems do - our systems are less prone to waxing, as the fuel in the tank will tend to stay hotter.

The fittings are horrid, but are cheaper at assembly time, as they simply snap into place. It doesn't help us who have to run them years down the line....

true but the point was why make it so complicated? whats wrong with it going tank-fuel heater-lift pump-filter-injector pump with cut off solenoid instead of tank-pre filter-lift pump-filter-stop solenoid-injector pump?
im sure the fittings are only cheaper to fit, not to make as the pipes cost around £10 ach and a jubilee clip costs about 20p!
as for bleeding the filter, i had a 1991 fiesta 1.8D which had no hand priming pump, a fuel filter which had no bleed screw on top, just a hose in from the tank, and a hose out to the injector pump, and it was never a problem, other than taking a decent crank to start it (like most MB's if you dont pre fill the filter) but other than that it was sweet. no problems with air in the fuel, in fact other than cam belts breaking if not chnged at the right time and the pulley kit fitted, the only real problems i came across with that engine was the leak off pipes used to perish and leak leading to poorer starting and poor fuel economy.

 

[Number_Cruncher]

>>whats wrong with it going tank-fuel heater-lift pump-filter-injector pump

Because our lift pumps do need the protection of the pre-filter to stop their valves failing or being jammed open by debris. Some similar designs of lift pump have the prefilter incorporated - but, if you did that on an OM606, you would need to work under the manifold to repair the pre-filter.

The rotary pumps with rotary vane transfer pumps aren't susceptible in the same way, as they are effectively sealed by the vanes passing large holes in the bore of the pump, instead of the small discs in our pumps which must seat all the way round to effect a seal.

For the layout of our systems it's a complex, but very good routing, and very thoroughly thought out. Once you've got the O rings sorted, there's very little that goes wrong with it.

I suspect our engine's fuel systems would still be working in temperature extremes where cheaper systems had long since packed up.

>>i had a 1991 fiesta 1.8D

It must have had a similar routing for the return - at least for the injector leak off, or else self bleeding would be all but impossible.

 

[turbopete]

>>whats wrong with it going tank-fuel heater-lift pump-filter-injector pump

Because our lift pumps do need the protection of the pre-filter to stop their valves failing or being jammed open by debris. Some similar designs of lift pump have the prefilter incorporated - but, if you did that on an OM606, you would need to work under the manifold to repair the pre-filter.

The rotary pumps with rotary vane transfer pumps aren't susceptible in the same way, as they are effectively sealed by the vanes passing large holes in the bore of the pump, instead of the small discs in our pumps which must seat all the way round to effect a seal.

For the layout of our systems it's a complex, but very good routing, and very thoroughly thought out. Once you've got the O rings sorted, there's very little that goes wrong with it.

I suspect our engine's fuel systems would still be working in temperature extremes where cheaper systems had long since packed up.

>>i had a 1991 fiesta 1.8D

It must have had a similar routing for the return - at least for the injector leak off, or else self bleeding would be all but impossible.

it went pretty much straight to the tank as far as i can remember. its 13 or 14 years since i had it now. the problems ive got with my current car, i sometimes i wish i still had it! loss of compression to the point of poor starting (cold) and non starting (hot) was never a known issue on those engines. not at 136k miles (mileage mine had on when i got it, now on 148k miles)

 

[pomm001]

The simple answer to all the questions raised 'why change ....' is because of emissions / fuel consumption and cost, nothing else.

Every addition second to assemble something adds cost, jubilee clips for example , they do not clamp evenly ( triangulate) and can give endless problems in engine assembly, OK for the garden hose but that’s about it ,spring band are preferred, quick and even radial pressure, when they are situated in difficult areas then push fit connectors are used. These are quite expensive but less problematic if buried under other components.
Great detail is paid to component weight, save two kgs on an engine and that improves fuel consumption, and so it goes on .
For instance I am currently working on replacing crank seals on an existing engine that have slightly less drag on the shaft, to progress this into production will be in excess of a million $ and take 24 months to save a miniscule amount of power absorption.
It does seem technology for the sake of it sometimes but how it is, the same for all manufactures
As an earlier post suggested that we have forgotten how bad things were 30 years ago

 

[steve--o]

sorry,not convinced

il stick with mi 38mpg plus 100 mph plus 300k plus 2.5 d
from an enginnering point of veiw,im affraid thair going backwards
filling underbonets fully of electo _mechanical trikery at great cost to keep the costs of servicing,owning,running high serving to keep the weekend hobiest or local small garage out .

S

 

[pomm001]

sorry,not convinced

il stick with mi 38mpg plus 100 mph plus 300k plus 2.5 d
from an enginnering point of veiw,im affraid thair going backwards
filling underbonets fully of electo _mechanical trikery at great cost to keep the costs of servicing,owning,running high serving to keep the weekend hobiest or local small garage out .

S

Convinced or not Steve that’s how it is
It’s a vicious circle, Governments keep reducing the amount of emissions,
To squeeze every last bit of power from the fuel, layers and layers of ECU's are needed to control all aspects of combustion.
Car companies hate spending money, if there was another way they would do it.
I agree that there is very little the owner can fiddle with now, as we know checking the oil level is a thing of the past, this adds to cost of ownership.
But then the governments get two bites of the same cherry, they force low emission on the manufactures and (UK) government introduce a 'retrospective' emission tax on cars up to 10 years old.
The whole thing is an income generator, I don’t know of another industry that’s had to deliver so many improvements over the last say 20 years.

 

[HERBIEMERCMAN]

i was design director for baxi uk, now biggest heating company in europe.

our reliability was based on cast iron boilers, low tech, run for ever, bit like the original land rovers.

the nett efficency for most of the cast iron boilers was circa 68%, could even be less when cycling on part load.

the current HE (high eff) boilers, circa 95% eff. are more like a tv set. turbo charged and condensate traps to discharge the water from combustion, no more latent heat to carry the burnt gasses into the atmosphere.

service costs become OEM (original manufacturer) based, due to monopolised fault tracing software, and spare parts, all very expensive. just the same as automobiles, sqeezing more from the fosil fuels is driving the technology, NOT, cost for the customer, and basic simple , reliable design. herbiemercman.

 

[teabag]

our reliability was based on cast iron boilers, low tech, run for ever, bit like the original land rovers.

30 years ago, I worked as a service engineer for the Northern Gas Board and agree Baxis were the most reliable although the most expensive boilers.

service costs become OEM (original manufacturer) based, due to monopolised fault tracing software, and spare parts, all very expensive. just the same as automobiles, sqeezing more from the fosil fuels is driving the technology, NOT, cost for the customer, and basic simple , reliable design. herbiemercman.

When a Bermuda 572 went down with anything but a pilot or thermocouple fault we had to call in the manufacturer's engineers as we were not trained in the "High Tech" diagnostic techniques required to fix them, also NGB would not carry a stock of Baxi OEM parts as they were so expensive.

Nothing much has changed over the last 30 years when it comes to dealing with "High End" manufacturers.

 

[steve--o]

Convinced or not Steve that’s how it is
It’s a vicious circle, Governments keep reducing the amount of emissions,
To squeeze every last bit of power from the fuel, layers and layers of ECU's are needed to control all aspects of combustion.
Car companies hate spending money, if there was another way they would do it.
I agree that there is very little the owner can fiddle with now, as we know checking the oil level is a thing of the past, this adds to cost of ownership.
But then the governments get two bites of the same cherry, they force low emission on the manufactures and (UK) government introduce a 'retrospective' emission tax on cars up to 10 years old.
The whole thing is an income generator, I don’t know of another industry that’s had to deliver so many improvements over the last say 20 years.

yes fair comment,i fully understand the "systems" need for food ie our taxes,espcialy the idiots running our once great now broken uk
but thair only able to tax it,A) becuase every body allows it, b) the motor enginners give them the tecno / means in the first place.

my own veiw is that if we were still on horses & carts,Pa Brown & co would have the vat man out with a horse poo sniffer, to make sure you had been feeding your beast green "taxed" grass

cheers
Steve ,in common sence exile, after 22 years uk self employed , now Spain