Cooling turbos - Afterun pump ?

[Dippy]

Not to cast aspersions on your "specialist's" knowledge, but I think there are some crossed lines here. My knowledge of oils is not great, but I think I do understand this issue.

The viscosity of an oil is determined by the ratings you quote. Although surely there is not necessarily a linear relationship between the two points, and there will obviously be a margin of error, the whole point is that a 10W40 mineral oil has the same operating viscosity as a 10W40 fully synthetic oil.

I think the whole point of mutigrade oil is that they are blended oils specifically so that the hot and cold viscosities are suitable for the vehicle and circumstances. I am not entirely sure on the process for manufacture of synthetics, however I believe it is generally a question of the source products, or rather whereabout in the crude oil refining (generally using fractional distillation), the products are taken from.

AFAIK mineral oils are directly derived from the heavier products and therefore contain components which are more prone to coking an engine. Whereas syntherics use the more refined products (and hence are more expensive), but are effectively "purer".

Because synthetics use more refined oils, of course by nature they have lower viscosity. But as I stated above, that is why they are blended to produce a multigrade.

So returning to the original point about viscosity being too low, I think this appears to be a fair point about the 0W30 grading that Audi have specified, but not about the oil being synthetic (remember that according to Audi, it is NOT mandatory to use a fully synthetic oil in the S4).

Based on the opinions I have received and the small evidence I have seen, I have also decided not to use 0W30 oil. I am currently using 15W50 oil, but may return to 0W40 oil in the winter (I am unhappy about using 10W40 oil in the winter - I do not have a race car - it is my daily driver and I need to use it as such). However my oil will always be fully synthetic - there is no way I will let a mineral oil anywhere near my turbos!

[Nige_RS4]

Dave, you're the offical post-whore on the subject of oil!

I agree fully with the above point - I was merely trying to raise awareness of the situation with 0w30 oil - clearly it didn't come across too well !!

[KayGee]

Synthetic oil, all the way, not only that, I change mine every 5K.

Anyone changed their gearbox oil?

[ajsl]

Sorry to resurrect this thread But does anyone (Nige?) know the part number for the new modified clip that Nige refers to earlier on in the thread (see below)?

One thing to point out is that there is a modified clip that Audi released for this sensor. The original one was plastic, the new one is metal...

Cheers

[SimonS4MTM]

Try this, 032 121 142, the one i have here is plastic covered but not sure if it is metal inside.

I have just got my parts to do this mod.

I also changed the coolant temp sensor a few weeks back due to a fault code. It uses the same clip and yes, it did break when i re-fitted it. A bit of an arse as i was 20 miles from my loacl dealer to get a new one. I ended up buying a couple just in case.

[ajsl]

Ideal, thanks Simon!

[kwottro]

Ah. I was wondering about that too. Thanks!

Have the other bits, going to do it this week...

[kwottro]

Clarification : Got the clip - it's actually plastic, not metal. According to the stores bloke at the local Audi place, it was changed from metal to plastic, not the other way around.

[ajsl]

Mine's on the way from VAGParts and htey confirmed Simon's part number as the revised clip, so I guess it will be plastic too!

[CliveH]

I'm convinced I have to do this too - can anyone advise Audi part numbers please?

Dippy, any chance of an explanation why the revs/boost have to be kept down on warm-up?

Cheers,

[kwottro]

I've bought the parts but haven't got round to fitting them yet. The following are the prices I was quoted a while back by www.vagparts.com are

021 919 369 – Thermo-switch £8.69+vat
N 903 168 02 – O-ring @ 32+vat

By the time they had replied I had bought the parts elsewhere and had paid much more.

Clip: 032 121 142.

Did mine saturday. Managed to empty the coolant reservoir onto the ground in the process - threw in another litre or so and hopefully now its all a-okay. Only been tootling around on short trips since, so yet to see if it does the job.

[Dippy]

Dippy, any chance of an explanation why the revs/boost have to be kept down on warm-up?

Simply that the turbos have an oil bearing. When the oil is cold, it has a lower viscosity that at operating temperature, and this means it is less reliable as a bearing. Hence if the turbine is spun very fast when the oil is cold, there is a risk of wear or even damage. I have no idea of the quantification of this risk, however certainly I don't think it's worth taking.

[CliveH]

Many thanks Dippy - that does it for me, although I have to say that I have always religiously followed this advice and I know that the guy who had it before me was just as careful (or so he said, and he did make a point of it when we took her for a testdrive), so I hope to have plenty of life left in my turbos?

[CliveH]

I've done it!!!

Now that might not seem much of an accomplishment for most of you, but for those of you who know my mechanical skills (no, you wouldn't trust me with your brakes upgrade!) will understand I'm quite pleased with myself! However, read on...

Although all went reasonably well with the removal and installation of the sensor, I'd like members to learn from my incompetence, just in case it's an easy mistake to make!

In terms of the removal, the guide posted on this thread is not entirely clear. There are 2 clips involved. As stated above, one is plastic and one is metal. The metal one is the one that holds the connector to the thermo switch body - the guide says that needle nose pliers should be used to pull this retaining clip out - on my car (2000 S4) this retaining clip works by pushing it in towards the connector, which releases it (not by pulling it out).

Once the connector is removed, you can get at the sensor by next removing the plastic retaining clip - this is easily removed by pulling in the direction shown in the guide. The next bit is the difficult bit because the sensor is well and truly held in place with the O-ring seal. It's fiddly getting the pliers in a position to be levered and then you just have to persevere until it eventually pops out.

OK, so eventually it's out and the guide says that installation is simply the reversal of removal. Well, that's true, except what it doesn't say is to make sure that the sensor (with O-ring attached to the bottom) is firmly seated in place with the plastic retaining clip sitting ABOVE the top of the sensor - yes, I know it's bloody obvious now but as I didn't pay attention (and don't have any "mechanics logic") and everything seemed to fit back together fine, I thought I had done the job.

So off I went on a short run to bring the oil up to temperature to test the new sensor. I stopped at the local Audi garage to admire an RS6 and as I walked back to the car I noticed a not insignificant pool of brown liquid accumulating under the front of my car! Ooops...

Yes, you guessed - I didn't seat the sensor firmly in its place and ensure that the plastice retaining clip was holding it in place. Result : the contents of the coolant reservoir emptying via the sensor.

I've refilled the reservoir with the correct concentration of G12 antifreeze, but I am left being a bit concerned about any damage I may have caused by running the engine for some 15 minutes with very little coolant - please tell me the worst or put my mind at rest.

Oh, btw, the upgrade does otherwise seem to have worked with the fan kicking in almost as soon as the engine is switched off.

[SimonS4MTM]

Finally did this mod as I had a week off work, and yes i can now hear the fan running