Carbon build up - Golf diesel

[ABCD]

Question for the diesel owners.
Golf 2.0 TDi. 45000km mostly city driving in a little over 3 years. In for service with Sydney based VW dealership.
Get call from service advisor saying that there is a lot of "carbon build up in the top of the motor", possibly result of stop start city driving and that this is very common with diesels due to all the soot they produce etc. I quiz him a bit on the diagnosis, specifically how they could tell carbon build up in the top end of the motor without removing valve covers/cylinder head etc. States that they can tell because there was quite a lot of "build up" in the throttle body etc etc and that he could show me some pictures of severe carbon build up in diesel motors (albeit not from my engine)!!
Anyway the "treatment" for this is to run special "de-carbon equipment" which hooks up to the motor and runs for an hour or so. Of course the workshop has this special equipment and yes they do have time to run it today and still have the car back to me as arranged. A little sceptical with the story thus far, I decide to not accept the kind offer to be relieved of $200 for the decarbon treatment.
Is a modern diesel engine doing typical kilometres per year really going to be prone to significant carbon build up, to the extent that this build up needs to be treated?? I thought the special engine oil as recommended by VW is designed to have a detergent effect on carbon build up etc deposited by the combustion process?
Can the special "de-carbon equipment" really do anything to treat the build up?
If this is such an issue with the diesels why would the VW factory not recommend it as part of the routine preventative maintenance in the service book?
The whole thing sounds like a load of BS to me - right up there with the special fuel and oil additives that get spruiked from time to time - but I would appreciate you guys' views on this.
Cheers

[JP2]

It seems very similar to my experience at 13k km service (petrol eng): was told "carbon build up in the throttle body" and cost $190+GST to clean. May I ask where did you send the car to service?

[gregozedobe]

VW TDIs are prone to getting a lot of oil and crap building up on the intake side of things (especially if they have EGR), but I don't think any of these "quickie" de-carboning processes are going to remove much gunk from the intake side.

Most likely they are just trying to drum up a bit more business

[ABCD]

It seems very similar to my experience at 13k km service (petrol eng): was told "carbon build up in the throttle body" and cost $190+GST to clean. May I ask where did you send the car to service?

McCarrolls Waitara.
Sounds like I was getting a slightly different story. I got a sense they were trying to claim the problem that needed addressing was carbon deposits within the engine ie cylinder linings/pistons/valves etc and that the build up on the intake side ie in the throttle body was the external "evidence" of the problem.
The "treatment" I was quoted sounds the same as you though (service advisor said "about $200" ie in the ballpark of what you paid).

[Greg Roles]

Welcome to the one major downfall of the TDI's.

They have two anti-pollution measures that cause this problem. Firstly the oil vapor "blowby", caused by the combustion pressure escaping past the rings and thus pressurizing the crankcase ( happens moreso in 18:1 plus high compression diesels ) is vented back into the inlet tract just before the turbo intake, to coat the innards of your inlet, intercooler, EGR / "throttle" flap and intake manifold. It gets burnt in the combustion process, which is the idea. Pain, but OK in itself.

Second anti-pollution measure is the recycling of exhaust gas. This is done to lower the combustion temps, and thus lower NO emissions. Problem is this "sooty" exhaust mixes with the aforementioned oil, and makes a nice thick black sludge, which does indeed coat the EGR inlet, "throttle" flap, and gums up your inlet manifold. At 40k I had a coating, but not buildup, but then I've been running a oil vapour "Provent" catch can since about 7k.

I'm sure the VW engineers themselves had to grin and bear it as the pollution crew would have had the final say. Long term problem waiting to happen, to keep the emissions down for passing the emission laws. Awesome huh?

I'd be suprised if at 45k you had any major problem, but certainly becomes a problem beyond 100k from what people have reported. I've hobbled my system somewhat, and long term it will all be removed, but responsibly so.

I'd recommend asking around both on here and at VW specific garages to see who else can offer a specific diesel spray clean, which does seem to clear the gunk out, and I'd bet you could get it a fair bit cheaper than what the "stealer" has quoted you. They may be guessing that you have the problem, and it's not an outright lie, but it may indeed just be an educated guess. They aren't at snake oil level of porky pies in my opinion, but it's a nice add on money earner no doubt.

If you search the diesel section, you'll see that we are mainly all talking about how to stop this sludge buildup from happening, as it's becoming apparent that it is a very real problem.

You could have a DPF as well like some of us, so you're actually lucky!

[Transporter]

Interesting thing is that it had happened just after the warranty.
If you had your car serviced regularly, you should contact VW Australia and ask "How is it possible that something like that can happen just at 45,000km?"

[ABCD]

Thanks Cogdoc for the comprehensive explanation which makes perfect sense to me. It is a pity the VW service advisor (service salesman?) was not willing (or able?) to share this knowledge. He was far too focussed on the "de-carbon sell job" ie wanting to show me graphic pictures of heavy carbon build up in stripped down motors but offering little if any credible explanation of why I should consider the special treatment. So by the time he got to explaining what the treatment involved he had lost me as a potential "sale".
(What I did learn about the treatment is that they apparently hook up gear to the air intake and spray some cleaner into it whilst running the motor for about an hour. I would still have my doubts whether this actually removes the build up, or indeed is worth $200, but am happy to do a bit more research and look at in another 12months/15000km of driving).


Transporter - the car is about 4 months out of warranty. The service advisor was quick to point out that the work he was suggesting was purely preventative, that there was not currently a problem per se and that nothing had failed. This plus the fact that they would claim this as "wear and tear" would see VW dismiss this as a non warranty claim, even if the car was still in the 3 year warranty period.

[gerhard]

This problem affects any direct injected engine, whether it's a diesel or a petrol. The reasons are identical - blowby gases and EGR gases are fed into the inlet tracts and accumulate. In both cases, since the engines are direct injected, there is no fuel passing through to keep the stuff dissolved.

Historically (for petrol engines), a carburettor atomised the fuel and this washed out the inlet manifold and ports, then came throttle body injection which did the same thing, then multiport injection also sprayed petrol into the inlet tracts. Then came Direct injection, and no more washed tracts, and a sludge buildup.

In the case of VW diesels, the engines are not fully run in till well past 60,000ks, and if they have been "pussy footed" since new, you may never achieve the best ring sealing possible, which will make blowby gases worse. I think there are plenty of diesels buzzing around towns & cities that are not properly bedded in, simply because they have so much torque - driving hard enough to bed the rings results in license loss too easily. Highway travel isn't much better, since again there is not much load on the engines.

Maybe they should provide a trailer load of bricks to hang off the back for the first 1000ks. More rings would be better seated

[Greg Roles]

True mate, but near double compression equals more blowby equals far more pressure, plus soot in the exhaust means the diesel is going to suffer a lot earlier than you gas types. I've never delt with such high crankcase pressure vapour actually, my BA GT had far less.

[brad]

Transporter - the car is about 4 months out of warranty. The service advisor was quick to point out that the work he was suggesting was purely preventative, that there was not currently a problem per se and that nothing had failed. This plus the fact that they would claim this as "wear and tear" would see VW dismiss this as a non warranty claim, even if the car was still in the 3 year warranty period.

Any reason you didn't bother taking out the extended warranty option?

Spraying "stuff" into the intake will certainly clean things out. I used to run water injection on my olde cars & it did amazing things.

I'd be inclined to do some minor maintenance sooner rather than later. This might be as simple as removing the piping before the inlet & spraying with some carb cleaner & giving it a scrub with a tooth brush.

You might also look at using something like Toyota Diesel Additive or Moreys Upper Cylinder Lubricant in your fuel. This won't help the inlet (direct injection bipasses that) but will help within the combustion chamber itself.

[gldgti]

this topic has already been very comprehensively discussed elsewhere:

http://www.vwwatercooled.org.au/newforum/upload/showthread.php?t=27155

cheers