2.5 TDi Rattle on cold start up, clears quickly.

[Carpie]

Hi there,

Hope I can ask a quick question and garner some opinions.

I have a 2004 B6 Cabrio with the 2.5 TDi V6 - we've had it just about a year and it's been mechanically excellent. Full SH and 4 months ago I had the following carried out at 101k with a recommended Audi specialist: Oil and filter service, CVT fluid change, air filter, pollen filter. I asked them to look it over and report on anything that may require attention and they said everything was in good order and a good example for the age.

Since the weather has been colder the car has rattled from cold start up. The noise is definitely engine related and I would guess its coming from the head. It always clears within 20 seconds or so, usually less, and once the car warms up it performs as usual.

My amateur's guess would be that the cold oil is taking too long to get to the valvetrain.

Anyone have any experience of similar symptoms on this engine and preventative maintenance that might stop it developing.

Many thanks all

Matt

Edit: Meant to mention, I have hooked it up to VCDS lite and scanned for engine codes but none reported. Also checked it with my generic OBD2 reader but no codes. It also smokes a bit on these cold start ups but I'm not sure whether it'd be termed excessive for a 6cyl TDi.

 

[AlexGSi2000]

I think the heads have anti-drainback / pressure relief valves which are supposed to keep oil in the heads whilst the engine is off.
Could also be that oil is taking too long to hit the valvetrain like you said - this may be down to a dirty oil pickup strainer (dont think the 2.5TDi's suffer with this issue though).

May also be that you have a lazy hydraulic lifter which is taking its time filling with oil.

These engines like to be set up correctly to be happy - they tend to suffer with camshaft wear if they have been on the long-life servicing in the past.

If you are local I dont mind taking a look over it for you.

 

[Mike B]

Do you know what oil they used?I like 5/40 fully synth

 

[adamss24]

The BDG engine is a quite robust wee engine but it still suffers from cams issues- they are hollow and the rings are pressed on which can slip or crack IF the timing belt is not fitted properly or the relay roller was damaged at some point- also common on 2003-2005 engines ! The replacement cams from dealer are solid, machined from billet steel and don't fail anymore- they very expensive though !
As mentioned, the likely culprit are the oil retention valves which are very, very cheap but quite involved to replace: turbo and injector pump off in order to make room to pull the oil filter housing off ! All in all is a very good engine which has been discontinued once they ironed all the bugs off !

 

[Carpie]

Hi all, thanks for the replies.

I think the suggestions of oil retention valves sounds like a likely culprit - as it sounds like a fairly involved job to replace them, would you say this is something I should do as a matter of urgency? Do you think it's causing much damage to the cams?

I have read about the weak camshafts on these and have been meaning to whip off the rocker covers to have a look at them - couldn't see any excessive wear via the oil filler though. Does seem a bit of an oversight by VAG to fit substandard cams. I'm guessing it must be one of the most highly stressed components in the engine really - you'd think the engineering standards required to build lasting camshafts would have been thoroughly researched and agreed upon by 2004! Was it a cost saving measure?

I cannot remember specifically which oil was used (the receipts are all in the car which has been borrowed by the OH tonight) but I remember doing the research and making sure they used the recommended type and conformed to 507.00 (IIRC?) etc.

AlexGSi2000 - the offer of having a look at it is much appreciated, unfortunately I'm in Surrey so a bit of a distance from Liverpool! But nice of you to offer mate.

As said, aside from this (hopefully minor and not causing further damage) issue, it certainly is a cracking engine. Great mix of poke and economy. I had the 2.4 Petrol in a previous B5 saloon which also was great but it didn't have the option of achieving 50+mpg pootling along on the motorway when you wanted to conserve fuel (according to the readout, who knows how optimistic that is!)

So, my last question really is: Do you think its causing much damage to the cams every time it's started from cold with the lack of oil or would it be minimal?

Cheers
Matt

 

[adamss24]

Hi Matt, pop to Chingford, N. london once and i will have a look at your car and advise you on what's the best approach in your case... regards,
chris