I have to disagree with edith on this one, use the oil recommended and I certainly wouldn't re-use the oil filter, false economy as far as I'm concerned....

On a standard OCI filter re-use might be a false economy, though its probably just a marginal economy. I believe 2 OCI are actually recommended by some manufacturers. (Filter performance improves as it gets loaded with contaminants, though of course it will eventually fill up)

I've never actually done this, but that isn't for any rational reasons.

In the context of unusually frequent oil changes due to diesel fuel contamination, it would be a real economy.

There would be a slight additional carry over of diesel in the filter, which is why I suggested draining it.

You'd probably need some implement to defeat the anti drain back valve. I'd probably use a chopstick.

Edited by edlithgow on 24/05/2019 at 04:20

Lowest viscosity protects the engine earlier in the warm-up cycle, just when most wear occurs.

That's an old one. Never seen any evidence for this oft-repeated claim.

If you have any sources on this, I'd be interested to see them.

To be fair, I havn't seen much experimental evidence to the contrary either, though I have seen some.

The general drift of informed opinion seems to be that, within the pumpability limits of the oil, which are seldom approached west of Novosibirsk, the positive displacement oil pump delivers roughly a fixed volume of oil per revolution, irrespective of oil viscosity.

EVEN IF this were true, in the current context

(a) The OP's oil is getting thinned by diesel. If you start with thin oil and thin it, you'll quickly end up with oil which is TOO THIN, and this will far outweigh any notional disadvantages of oil which is "too thick".

(If you think oil can't be too thin, then diesel dilution is presumably no problem, except (b))

{b) If the engine runs away and wrecks itself, this will far, far outweigh any notional disadvantages of oil which is "too thick".

"Changing oil viscosity to fix a DPF issue is the wrong answer, IMO."

Clearly it isn't a "fix" at all. Its a partial immediate action work-around. As someone pointed out above, the most reliable "fix" would be not buying one in the first place

"Only fully-synthetic meets modern requirements for cats and DPFs."

That's a new one. For cats I'm pretty sure it isn't true.

As I understand it, DPF's require a low SAPS (basically, low ash) oil. The ash comes from the additives, not the base stock, so there isn't any obvious reason why it can't be achieved with conventional oil.

(This assumes the conventional - synthetic distinction means anything, which is doubtful outside a German legal context. "Fully synthetic" to me implies actually synthesised, and if thats what you mean, your statement is even less plausible, since that is pretty rare)

Edited by edlithgow on 24/05/2019 at 04:09

thanks all for the replies. I have spoken to the service manager and customer service at Audi who all say this is normal and they will not be paying for any diagnostics on the car. customer service spoke to technical experts who I assume is the garage it went into ....

yeah, live and learn. I mentioned the DPF to the sales guy and he said just take it for a spin on a local A road near to me once in a while. the service manager said I should never have bought it !! ah well. only 3 years of PCP left ....