dci problem rumours.

[Gazwould]

On another marquee forum something about turbo failure because of faulty egr , C02 in exhaust gasses cooling effect ?

And if battery fails the power steering is lost and has to be coded back in by the main stealer ?

Please confirm and expand.

[AlexB]

No, the both points are not true.

EGR reduces only the peak temperatures inside the combustion chambers, while slightly decreasing the efficiency of the engine. In order to maintain the same power output under reduced efficiency one has to burn more fuel, which may actually increase the exhaust temperature under high EGR rate. So, it's the opposite to what you wrote... EGR is only needed in order to reduce NOx emissions, which is done at the expense of reduced power output, increased fuel consumption and increased soot emissions. In majority of cases the turbos blow due to use of mineral oil, falsely advertised as synthetic, and incorrectly set oil drain intervals. EGR systems cause trouble when oils susceptible to polymerisation are used, i.e. mineral or fake synthetic, because they form a resin when combined with soot and exhaust gasses.

After disconnecting the battery programming of the steering column is not lost. However, it enters a calibration mode, in which one needs to point the wheels straight, then turn the steering left-right by 90 degrees. If this is not done, I guess, it will use the old calibration values. Never tried not doing this, as it is described clearly in the manual. This thing is not specific to DCI.

[Gazwould]

Copied from HONEST JOHN . CO.UK

On 1.5 and 1.9DCIs EGR valve should open to allow carbon dioxide, which acts as a cooling gas) into the combustion chambers when the engine is under load (>30% boost). This allows the combustion chamber temperature to drop and thus the temperature of the exhaust gases. If it sticks in the closed position the exhaust gas temperature will rise causing a) the turbo bearings to fail and b) engine oil into the induction system. This will cause the engine to go on running until it has consumed all its oil and then it will go bang. Problems with EGR valves in Renault dCi engines are often the cause of rough running when the valve is stuck in the open position as well. In several cases turbos have blown but the EGR valve has not been replaced. Inevitably the new turbo unit will not last long. This seems to be confined to early 1.5DCIs as Renault modified the EGRs and no further reports of trouble in the 9 months to April 2007.

[AlexB]

It's not a proper source of information, and the explanation does not make sense.

[Gazwould]

Not a proper source of information, lol.

You won't get the truth from the stealers who rarely put there hands up to a problem.

It's making sense to me.

A Scenics turbo let go and feasted on its own engine oil juring an mot smoke test !!

And why a Nissan Qashqai was on its 4th turbo.

[AlexB]

So what? Turbocharger failures are always accompanied with oil escaping through the seals. Regarding repeated failures - the garages do not look for the root cause of failure, so the problem comes back. The cause is usually the lubrication system. I'm yet to hear about a turbo failure with PAO or ester based oil changed every 9k miles or annually, whatever comes first.

[Gazwould]

So the HONEST JOHN website, Which? and alike are all lies then !?

[tomalamix]

Despite the Honest John reputation there is no sense there...as Alex told the EGR is not to cool (error in Honest John) the exhaust gases, is not to let the gases reach higher temperatures, the valve lets a small percentage of exhaust gases to come again into the intake (exhaust gases doesnt have oxygen to burn) so the burn will not be able to reach higher temperatures because there aren't enough oxygen inside. This is done because higher combustion temperatures produces NOx (several types of NO ) in high quantity, its a EURO 2 or 3 demand.

Now, if Honest John website claims that a EGR can break a turbo if its malfunctioning i would to like to see the explanation about that, i like to learn. Do you think that is possible? Lets see...a completly clogged EGR = car doesnt work so no turbo failure possible; Stuck open EGR = car strugles to be alive because too many CO2 inside chamber instead of Oxygen - no turbo failure; EGR completly close = nice, more power outpowet but the environment regulations are not met - no turbo failure; EGR clogged from the exhaust side - same as stuch closed EGR- no turbo failure; i think honest john have some other possibility where i dont see more.

Ithink it is a good thing for all of us that like me and Alex that believe that low oil quality decreases the life spanner of the turbos. Please be aware that the turbo bearings (and shafts but far less) also worn up, but they stand there for a big mileage if good oil and good oil changes intervals are preserved.

Lets all wait for the explanation from Honest John, shall we? This will let us know more about EGR and how it can blow turbos. Thank you in advance!

[AlexB]

Hi Tomalamix,

It's not quite what I meant. EGR does not starve the combustion process of oxygen. It is still burning lean, as any diesel. EGR just slows down burning, which, as a result, does not reach very high peak temperatures. This is to reduce NOx formation. Its the same energy, but released over a longer period of time.

This peak temperature has nothing to do with the exhaust gas temperature (EGT), as it becomes lower when the piston is travelling down. Remember the laws of thermodynamics? In fact, EGT remains almost the same under different EGR rates for a fixed power output. Minor deviations take place due to the increased burning time.

If the EGR rate is cleverly controlled and reduced at idle or high loads, then its effect on EGT is minimal. EGR is known to increase soot formation and reduce power output. The former issue is addressed by using particulate filters, and the latter by switching EGR off at high loads.

Note, if the EGR valve stays open under high loads and high revs, then flames will be thrown into the exhaust due to slow burning. This will increase EGT and reduce power. Cars, however, are rarely driven at full throttle and the revs are limited... This is the opposite to what HJ wrote, isn't it? Regardless, the turbos in diesels are not running red hot anyway, and can tolerate quite a lot of overheating, such as when DPF regeneration is performed, for example.

EGR gasses, by the way, are hot. This is the opposite to the intercooler action. In some engines, not Renault, these gasses are cooled down in a special heat exchanger (in Alfa diesels, for example).



The other misunderstanding is concerned with oils. Almost all bearings in the engine use hydrodynamic lubrication, which means there is no rubbing involved. The role of oil there is to act as a fluid on which the bearing surfaces are gliding. If the oil goes bad, its pressure drops and the metal surfaces "land" on each other at high speed. This happens if a piece of dirt or sludge starts travelling in the oil channels.

Sludge is only formed in mineral oils, even the most refined ones, which are sold as cheap synthetics. The oils made with esters or PAO base stock do not form sludge and do not polymerise like the black stuff on your frying pan. Therefore, they are better for the hot applications, such as turbos. Just read a couple of books on tribology to get an idea.

[mickeybo]

Big end bearings & turbo bearings just to simplify things Both of these run on a cushion of oil between the crankshaft journals & the big end shell bearings

[tomalamix]

i get both ideas, wither way it doesnt blow turbos...

I'm still waiting for the Honest John theory about this EGR blowing turbos...lets waint and see how that is made.

cheers

[den9112]

Some good reading their Alex ,as you know my turbo as just gone ,from now on I am going to pay the small premium and make sure I get the correct oil for my car ,no more cheap so called fully synthetic.

[MilosB]

I have also just replaced the turbo and wonder if elf premium 5W-40 is good for 1.9dci?