Cooling turbos - Afterun pump ?

[TarmacTerrorist]

MMMmmmmm.....So will it fit my car or not??

Need to get this clear anyway as Im a little unsure what the after run sytem actually does -

My understanding of it is that the turbo bearings (perhaps other parts within them), are cooled and lubricated by a forced oil feed that runs when the car is runnning.

If you go tear arsing down the road for ten minutes spooling your turbos upto 150,000 rpm or whatever it is and just shut the car off, the oil feed stops and the residual amount that is left within the housing bakes and crystalizes on the components, which in turn wears away the seals and bearings prematurley...???

Sound like this afterun sytem runs off the water temp and just continues to pump water round the engine block when activated, or does it incororate a system to keep a flow of oil going into the turbos??

or am I talking pish posh...

[TarmacTerrorist]

Phil t has an after run system (on his alarm i think) that continues to run the engine for a few minutes well after the keys are removed and doors are locked.

[Nige_RS4]

Sound like this afterun sytem runs off the water temp and just continues to pump water round the engine block when activated, or does it incororate a system to keep a flow of oil going into the turbos??

It continues to pump water around the turbo jacket (our turbos are water-cooled) which in turn should help fight against the aforementioned heat-soak problems with the oil in the turbos.

Probably not the best explanation, but there again, it is 9AM.

[KayGee]

According to ETKA the RS4 uses the same thermal switch as the S4 so yes it will. The problem is the turbos get really hot after turning off the car, and the stationery oil in th eoil lines feeding the turbos gets carbonized, reducing the diameter of the oil feed lines and thus reducing the oil supply to the turbos.

The after run pump only runs if the water temp goes above 112c (93c modded). The afterun pump, as Nige says runs coolant through the turbos to help remove any excess heat and stops the oil from carbonizing inside the pipes and turbos.

[kwottro]

I know they are small, but 150,000 rpm sounds a bit exaggerated
Just out of interest, does anyone actually know how many rpms a K03 can get up to ? Sounds like it would be a good pub factoid to know !

[Dippy]

Where's Dippy when you want him eh?

I can't spend ALL my time on this site!

I think it's all been covered now. However I can add a little more information.

I think I was the first in the UK to force the afterrun pump on. However my mod was done before that rather helpful article about the sensor, so I have used a turbo timer. The sensor is a normally open "volt-free switch", and turbo timers generally switch 12V, so I used a relay to short out the sensor and force the pump on. However I decided that I didn't want the sensor shorted whilst driving, so I hooked up another relay to isolate it when the ignition is on.

Whilst I think the sensor change is a good idea, it is worth noting that it is NOT the ideal solution. The sensor only measures the coolant temperature, and the oil temperature, expecially round the turbos, can be a LOT hotter. Since AFAIK coolant cools much quicker than oil, it means that even with the lower rated sensor, the oil may still be quite hot when the afterrun pump cuts out, if the turbos get very hot.

My turbo timer is also a boost gauge and it varies the timer value according to how much boost has been used. Normally this is OK, but not IMO during hot weather. This is when I switch it to manual to be sure I get proper cooling.

Another thing I can add is a little technical information about the afterrun system:

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.

This is covered in the Audi self-study guide for the 2.7 biturbo.

[DavidT]

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

Thanks Dippy,

So the afterrun pump exists to protect the turbo water cooling system on switch off, not the turbo oil system ?

If so, what is the benefit of modifying it to trigger at a lower water temp ?

[Nige_RS4]

There is a benefit, which is to prevent heat-soak of the oil in the turbos by forcing water through the turbo casing for 10mins - this time is fixed, regardless of any temperature drops or your driving style.

I still see it as a beneficial mod, however it cannot and should not replace careful warm-up and cool-down techniques, unless you can afford a £3k turbo swap.

[KayGee]

As Nige says coolant flows through the cooling system, coolant absorbs the heat from the turbos and moves it away from the turbos and stationery oil, stopping the oil from cooking and leaving deposits, the deposits slow the flow of the oil to the turbos. Turbos without oil make nasty noises and fail, very quickly.

Majorly big benefit = saves you thousands of pounds in turbo replacement bills. Downside costs £15. No contest in my book.

[Dippy]

There is a benefit, which is to prevent heat-soak of the oil in the turbos by forcing water through the turbo casing for 10mins - this time is fixed, regardless of any temperature drops or your driving style.

I still see it as a beneficial mod, however it cannot and should not replace careful warm-up and cool-down techniques, unless you can afford a £3k turbo swap.

Nige, that is not quite correct. It will turn on the afterrun pump and electric fan for a MAXIMUM of 10 minutes. If the temperature lowers across the threshold before then, they will switch off.

That's what I meant: Even with the lower temperature sensor it is still controlled by the water temperature and not the oil temperature.

I also agree with you. It does not really replace proper cool-down driving (but can seriously reduce the extent), but more importantly it does nothing about warm-up. And it is the stress caused before proper warm-up that is the bigger risk to the turbos!

[Dippy]

So the afterrun pump exists to protect the turbo water cooling system on switch off, not the turbo oil system ?

If so, what is the benefit of modifying it to trigger at a lower water temp ?

I haven't got the self-study guide to hand, so I'm not exactly sure what it was intended to protect. All I remember was that it reverses the flow in order to dissipate air bubbles. Presumably, just as in a hot water central heating system, a large collection of air bubbles could cause an airlock, so it is more a question of keeping the whole coolant system working.

However as noted, the turbos are included in the coolant system, so this afterrun system also cools them at the same time. Using a lower temp sensor or by overriding it like I do, you have an instant turbo cooling system.

[SimonS4MTM]

Is it not possible to mod the switch wiring in someway, so that the pump always activates irrespective of temperature

[KayGee]

Simon,

Shorting out the switch would mean the pump runs continuously, not good for the battery. Also I agree with Dippy, it runs the coolant in reverse to dissipate bubbles created by the high temperatures of the coolant (112 deg c) so the afterrun pump would be fighting the water pump. Meaning you would need to reverse the polarity and add a timer circuit. IMO opinion the existing circuit is good design, only runs when car has been "exercised" and coolant is a few degrees above normal (90 deg c) running temperature. If you wanted to run the S4 cooler you could replace the coolant sensor with a lower rated one.

It doesn't run for very long in my car, usually cuts off in a couple of minutes max. Maybe in hotter climates it might run for longer.

Allowing the oil to get upto temperature is vital in any turbo charged car, not just the S4.

Have to say my oil temperature is no longer a concern since the RS4 oil cooler was added. Works brilliantly, oil is temp is now pretty much constant around 80 dec c. However this mod is slightly more than £15.

[NeilMc]

I might be taking this thread in another direction now, but what can be done to prevent damage to the turbos right after starting the car? I try and take it easy for a few minutes, but sometimes there's a bit of open road, and in rush hour you just can't help yourself. I don't fancy using a remote starter because firstly I'll forget to use it, and secondly it'll interfere with my tracker.

[DavidT]

[quote="NeilMc"]I might be taking this thread in another direction now, but what can be done to prevent damage to the turbos right after starting the car? I try and take it easy for a few minutes, but sometimes thereNothing really, sorry.

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.

I am not a fan of any kind of remote start as they warm the engine at idle, i.e. it takes the maximum amount of time to reach normal operating temperature. Most wear in engines is caused during warm up (around 70%) so it is far better to warm it with gentle driving.