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VAG TDi engine reliability - Tim T
I have had an A4 TDi 90 for two months, it had done 104,000 miles and I've put another 3000 enjoyable miles on it since.

Has anyone got any tips about maintenance, that goes further than Audi and Haynes manuals? I'm already doing 5,000 mile oil changes like the last owner. I plan to keep it a long time if it's viable so preventative maintenance is well worthwhile. I'm looking for a good garage in either the Harrogate or Carlisle area, I live in one town and work in the other.

Tim T
Re: VAG TDi engine reliability - Guy Lacey
Change the injectors.

Use a good (VAG) oil and filter.

Don't just "check" the cam-belt every x-months/miles (36/40,000?) - change it!

Drain water from fuel filter regularly.

Don't *under*rev - drive it as it should be driven (1,000 - 5,000rpm)

Minimise short journeys.
Re: VAG TDi engine reliability - Alvin Booth
Guy,
I would agree with all you say apart from the bit about revs.
Have heard this many times but remember that HGVs usually rev at max around 1800rpm and its not unusual to see these with a million miles on the clock. One of the reasons given for revving is to avoid a build up of carbon in the combustion chamber but I think this applies more to the olden days when fuel used to coke up the valves in about 10000 miles.
I remember the old TS3 two stroke diesels fitted in Commer HGVs used to dekoke themselves periodically.
Quite a sight to see in the mirror at night when the exhaust used to suddenly start blasting out sparks as if Vesuvias had erupted. This would last for a few minutes and the job was done.
vauxhall suggest that the Vectra be normally driven between 2000 and 3000 revs to maximise fuel efficency and minimise engine wear.
What benefits of using revs are you suggesting Guy.

Alvin
Re: VAG TDi engine reliability - Stuart B
I would generally agree with Alvin except part of the reason for HGV longevity is not just the low revs but they are also driven with wide throttle openings.
What I am talking about is preventing bore glazing by blasting out the soot.

Years ago I first got aware of bore glazing on yacht diesel engines. Almost exclusively the owner had used the engine for battery charging which meant long periods running at constant revs under a light load, ie in neutral. Being impecunious yachties and mostly Yorkshiremen to boot all means, fair and foul were used to try and cure the problem once it had occurred. In the end we decided THE only solution was to hoik the motor out, rehone the bores and fit a set of oversize piston rings. Owners were advised that to avoid the problem in future only run the engine for long periods under a decent load and vary the revs to try and use as much of the operating envelope as possible. Plus to install a decent battery charging system rather than the auto based alternator.

What has this got to do with cars I hear? Well the reason that cars get this effect less is because in normal use the revs vary and the throttle opening also varies, plus the engine gets put under a decent load when accelerating. Plus as Alvin rightly said auto diesel is generally cleaner than tax free marine diesel. (Government got its finger on the environmental pulse there...I think not) BUT the exception is when the driver is particularly feather footed. By trying to be economical you can still end up with a big bill even with ULSD.

Therefore Alvin is right to say the car will drive best if revs typically 2000-3000 are used, and Guy is also right when he says a good blast will help. Also it does not hurt from time to time to have a bit of low revs full open throttle work so as to get the engine really working.
Re: VAG TDi engine reliability - Alvin Booth
Stuart,
Yes you are quite correct with your comments on bore glazing which as you say is due to light load running of the engine.
My wifes car is a Maestro TD which has the Perkins Prima diesel engine.
I imagine you are very familiar with this engine as it is used in marine applications.
I have the manuals for this engine both in vehicle and marine form and yes Perkins say that the engine is to be put under full load immediately for the very reasons you state.
However full load and revving of the engine is not he same thing in my mind.
Full load is when the engine is exerting power against resistance whether it be a car transmission or a boats propellor in the water.
The same thing is large emergency generators such as used in various establishments.
The instruction for these used to be put under full load after 30 seconds.
However when the keys were turned to connect the full KVAH on to the system the revs on the engine drop by about a third and the sound of the engine (often a Gardner) would indicate true load which is just what a diesel does best.
I think we are both coming from the same direction Stuart but my main theory is that rpm and load don'y necessarily equate to being the same thing.
I believe that an engine can be running on high reve and light load.
Once again to mention the TS3 two stroke diesel engine (The TS apparently stood for Tiller Stevens which was also a marine design) When this engine was uprated in about 1962 problems arose with the bores not bedding in resulting in large amounts of blue smoke from burnt engine oil.
The manufacturers advice to cure this was to load the vehicle heavily and allow it to labour.
This engine was an horizontal flat cylinder engine and the theory was that by allowing it to labour badly it would encourage the cranks to flex and force the pistons against the portion of the bore which wasn't getting the equal pressure of the piston rings due to it being an horizontal opposed three cylinder with 6 opposed pistons. I'm sure you get my meaning Stuart.

Alvin
Load vs Revs - Guy Lacey
Let me clarify!!!

Having owned a number of diesels I have to say the best are those that have been driven well. I once picked up a 306DT that had been pottered to the shops now & then by some farmer's wife (straw in boot, feed sack on floor, etc) I took it out of that garage on a test drive and up a steep hill in third to give it welly - it smoked like a London Bus.

I agree - flat out revs is not what you need - just, form time to time, let the engine work as it should.

I assume diesels work at their best under high load as a result of the adiabatic compression principles at work.
Re: Load vs Revs - David Woollard
I bet you've been waiting months to slip that into a diesel thread.

David
Slip that into . . . . . . . - Guy Lacey
Not as long as I've been waiting to slip it . . . . . . . . . .


No, sorry.
Re: Load vs Revs - Stuart B
I think we are all saying more or less the same thing here.

When I was saying giving it a blast I really meant taking the car out and giving it some stick, high acceleration loads, and taking it up briefly to high revs. Also high loads at low revs, in other words use the full operating envelope, even if you only use a part of it for most of the time eg 2000-3000 revs, with throttle positions commensurate with the traffic flow at the time.

The engine subject of Tim's enquiry is already well run in hopefully being @ 104k. Therefore what we are saying is that to provide longevity is to drive it normally, use the torque which means low revs compared with a petrol engine and put the engine under decent loadings.

BTW it is quite interesting that recent research from Sweden says its also of benefit to petrols re economy to change up early and use wide throttle openings. Is this the beginning of the end of the diesel vs petrol debate?

Being fairly light footed, Yorkshire upbringing you know, I still think that diesels like petrols benefit from time to time with a brief Italian tune up even if its only to blast out the soot from the system and get the oil really nice and hot. Well that is my excuse for going for a blast and I'm sticking to it. ;-)
re: fuel injectors - Tim Guymer
So how much should I look to pay to get the fuel injectors changed approx - own a 130k Vw Golf TDI. Is it a job for a dodgy diy-er? Or is it best left to the garage? Joining the torque debate the 90bhp tdi seems to have a fair turn of speed @90mph which is about 3,650 revs -useful on the autobahn's...
 

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