Cooling turbos - Afterun pump ?

[NeilMc]

I guess that's what I was expecting to hear. Only problem is I just physically can't stop myself sometimes. The money should worry me as I'm paying crazy finance payments on the car already, but I end up thinking oh well, if they go they go.

Oh, and it takes a good 15 minutes for the needle on my oil temp gauge to even move, and it never reaches 95. I drove to brighton (from manchester) and it was only just around there... is this normal?

[eatthis]

The actual reason why the pump exists and why the temperature sensor seems high, it that it is designed to remove air bubbles from the coolant system that can occur in the turbo water jackets when they are very hot. So the afterrun pump actually reverses the coolant flow so that these air bubbles are dispersed in the engine block.

im fairly sure my mk3 vr6 has a similar system its an auxilliary water pump that runs for a while if the engines still hot

[S4driver]

[quote="DavidT]

Best advice is to stay off the boost (boost gauge reqd) and try to keep the revs below 3k until the oil is at its normal operating temp, which for me is around 95c. This is 10 minutes driving at least.

[/quote]

Well thats handy, as mine barely sees over 2k

[KayGee]

Right a few clarifications, this system will only trigger if the coolant temp is above 93 deg c. In order to "achieve" this the car must of been driven hard or run in high temp climate. During normal (non turbo activated) driving you will not have the afterrun pump run.

S4driver this counts you out.

The temperature of the engine bay is highest when the engine has been turned off for a few minutes. Why? Because the cars active cooling system is no longer working. There is no coolant flow arount thew engine and no air flow through the radiator. All the latent heat held in those systems and the hot components is radiated off to the atmosphere, slowly.

The biggest potential of source of localized heat on our cars is our turbos, when they have been working and especially so when they have been working hard, even more true for chipped cars running K03 turbos. These components can glow red hot.

The oil temparature and coolant temperature senders are located remotely from the turbos and measure the overall oil/coolant temps. When the engine is turned off they are measuring the temp of the oil/coolant in the systems local to them. The oil and coolant is no longer circulating and dissipating heat evenly. With hot turbos the oil and coolant in and around the turbos can be significantly hotter than the oil and coolant elsewhere in the system.

This isn't a problem for the coolant, worst case it boils, get a few bubbles, no big deal, these are quickly dissipated. Oil however when heated above certain temps breaks down. Essentaially burns. When this happens, the oil deposits a layer of carbon materials. This is bad for a few reasons.

It reduces the oils ability to lubricate, worse still it reduces the flow passages in the turbos oil ways and oil supply lines, lastly you have carbon deposits on the metal surfaces, including the turbine shafts.

This behaviour repeated time and time again will result in oil starvation to the turbos turbine shafts. Big hole in pocket.

This is most likely to happen at startup and turbo failure will be the result. Turbos are dependant on getting a good supply of oil in order to spin at the required speeds in order to produce boost.

All we are doing is triggering the system at a lower threshhold to ensure the coolant absorbs excess localised heat from the turbos and moves it into the main engine block and cooling system where it can be dissipated safely without causing the oil to breakdown. Most modern turbos are water cooled. Oil is primarily used for lubrication.

Turn your ignition on ten minutes after turning it off after a long drive, don't start it. Look at the oil and water temperatures. Now imagine how hot the coolant and oil get inside a red hot turbocharger. Now spend the £15 and half an hour it takes to do the mod.

Apologies for the long post, hopefully this clears up what conditions the mod is designed to address, how and why it will trigger.

What else can you do to help minimize the risks? Use the right oil. Change the oil reguarly. I change mine every 5K. Don't use WOT until the oil is upto temperature. Insulate the oil lines with heat wrap close to the turbo. Allow the coolant system time to dissipate the heat in the turbos before shutting off the engine.

Most modern Audis have this afterrun safety system to remove air bubbles form the coolant system, we are using it for a different purpose. On the 1.8T Audi use it they same way we do, to cool the turbos.

[eatthis]

what is the operating temp for the oil on an s4? when is it safe to use wot?

[Dippy]

Of course it depends on driving style, however with "average driving", during winter 80-90 and during summer 90-100. I find that a long motorway drive will push it up 10 degress.

As has been described about, it is difficult to resist using the turbos until the oil as at operating temperature. I certainly treat it gently (which means off boost or only say 0.1 or 0.2 bar) until the oil gauge needle starts to move. Then I will allow a bit more (maybe up to about 0.6 bar) when it is nearly at the 80 mark. At this point it will only be a minute or two before its fully ready to go

[Dippy]

On this subject, I have had one S4 owner admit to me that he didn't really follow a warm-up/down regime, and had to replace turbos. Anyone else had turbo failure willing to be honest?

I have always been careful about my oil changes and following warm-up/down. My turbos have now done over 50K and seem strong (no sign of worrying noise and have the same light whistle on spool-up as they did when the car was new).

[KayGee]

My turbos had done 56K when they came out (last 14K were mine) and appear in excellent order, light whistling on spool up which was more noticeable with APR downpipes installed. K04s whoosh rather than whistle. Again, 5K oil changes and not used in anger until oil is warm.

Mine used to be 80-100 depending on how heavy my right foot is.

Bedford Autodrome saw the oil upto 120 degs.

[kwottro]

Excellent and helpful info guys, especially Kaygee, thanx. I picked up the new thermoswitch yesterday, will change it ASAP. Looks like the next step is to get a boost guage installed to keep track of exactly what the turbos are up to. Any recommendations on brands (European) ? I imagine this is a little more costly and requires a bit more expertise...?

[NeilMc]

The AWE vent mounted boost gauge is popular (and probably the one I will choose). Good tech articles on audiworld detailing the installation... or have AMD do it for you.

[KayGee]

I just bought the APR one from ECS in the US, AWE one is very popular or if you're a whizz with a dremmel, buy a spare vent pod from www.vagparts.co.uk and make your own.

[UKS4APR1]

I used an "OMORI" guage purchased direct on-line. It's a "multi-coloured" one which means you can select lighting colour. Obviously mine's set to RED has white needle and is perfect match with other dials. I have early style dash and mounted it in the small cupboard/coin-holder position.
I also have the after-run pump mod which I think is a good idea as it can only help with heat soak. Beware...you need a good Battery!! The fan can run for 10 mins and run an old battery down to the point your car will not start!!

I take care best I can warming-up the Turbos on my S4. However just to fill you all with confidence, let me tell you I have had two Turbo vans for work (Citroen and currently VW). I start my van every day in all weathers including sub-zero. The van is leased by the company I work for.

Every day the van gets flat-out full boost immeadiately with no warm-up cycle whatsoever, just full whack wherever possible and straight up the motorway within 4 miles. The last van covered 90,000 miles without any problem with the turbo whatsoever and the current one is doing fine also. Oil changed at recommended intervals (more than 10k) with "normal" oil.
This is what helps me to quell my paranoia and was a deciding factor when buying the S4!!!

[Nige_RS4]

However just to fill you all with confidence, let me tell you I have had two Turbo vans for work (Citroen and currently VW).

I'm assuming that they are turbo diesels, which aren't stressed any where near as much as petrol turbos both in terms of heat and max rpm. Modern diesel turbos have electronicly controlled vanes which allows them react quicker - this is not possible with petrol turbos due to the massive heat ranges involved.

I put "normalish" oil in my S4 every 5k - been warned off fully synthetic by my local specialist.

[kwottro]

Nige, what do you call "normalish" oil ? Your last comment intrigues me, as I have also been 'researching' for the right oil to use, and this is currently being discussed on another forum. Who (or what) is your specialist, and what where his reasons for not liking synthetic oils ? I'm a long-time fan of Mobil1 0w40...

[Nige_RS4]

My specialist races VW/Audi turbo cars and uses something like 10w40 oils. Modern synthetics have a very thin viscocity which don't suit the charactertics of turbo engine - there is much debate about this, but I think I recall a good thread on this site about this (if you can find it).