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D2 - Transmission Gearboxes, diffs, drive shafts.

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  #11  
Old 21st August 2019, 03:02 PM
spannerrash spannerrash is offline
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So that all went OK. The flow out of the cooler / radiator is definitely out at the top.

Not fully understanding the oil flow route though the gearbox, I don't know fully how effective this is but I feel I have done the best I can from a DIY point of view to Clear as much old fluid from the system as possible.

I've not finished the refill procedure yet as I had to break off to do some other stuff.
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  #12  
Old 21st August 2019, 03:11 PM
MikkiJayne MikkiJayne is offline
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How is the pipe in that orientation?

Have you just pumped everything out of it by running the engine?

Curious to see how much you get out / how much goes back in by doing this.
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  #13  
Old 21st August 2019, 03:33 PM
spannerrash spannerrash is offline
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The pipe was fine in this orientation and yes I ran the engine to pump it out.

It's a time consuming process though because you don't want to run the pump dry.

I pumped out approx 2 litres and then went back under the car to refill the pan. I repeated the pump and then refill 5 times.

It's very wasteful when it comes to oil and to be fair the color of the first sample taken compared to the last wasn't as dramatic as I expected. That said, the genuine Audi oil seems to loose its clear ish colour very quickly in my experience.

By the time I had finished I pretty much filled the orange bucket you can see.
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  #14  
Old 21st August 2019, 03:39 PM
spannerrash spannerrash is offline
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Just to be clear. I have just replaced the filter and front lower valve body so I am starting with an empty ish system.

I only have 3 litres in the pan plus what's in the rest of the box when I start the above process, thus I only take out 2 litres at any one time.
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  #15  
Old 22nd August 2019, 02:52 PM
spannerrash spannerrash is offline
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Before and after results. 18 litres of oil put through the system.

Take this with a slight pinch of salt though as I have not road tested the car yet. As I am working from axle stands its not practical for me to keep lowering and lifting the car.

I have though wormed up the gear box twice and run the selector leaver through all the positions on both occasions.

The question now is if this new fluid helps or hinders the gearbox. I'm not a believer that new oil will damage a good box but I do believe it could make a bad box worse.

My box had no issues and no fault codes before starting this process. This was simply a preventative maintenance job. Unfortunately, on dropping the pan there was much more debris on the magnets than I was expecting.

This may help it or kill it.

I'll update as soon as I find out.
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  #16  
Old 7th September 2019, 03:06 PM
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27litres 27litres is offline
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I reckon MJ might know the answer to this one, but does the transmission have a thermostat controlling flow to and/or from the cooler?

If so, this may answer two questions, the first being will an additional cooler cool the transmission too much (the answer being no, if there's a thermostat). The other question is why does the transmission need to be at a specific temperature when filling - I don't buy the oil expansion theory, but making sure the thermostat is open to fill the cooler makes sense.
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  #17  
Old 7th September 2019, 03:41 PM
ainarssems ainarssems is offline
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I used to think that there is thermostat in the box but was not sure and looking at previous posts it seems like there is no thermostat in the box.

In regards to thermal expansion different fluids will behave differently in different temperature ranges.

I vaguely remember reading it somewhere that for the 5HP24 box with about 12l of ATF the volume from cold 20C to working temp of 100-130C will change by 0.7-1l.

I also know that different engine oils expand differently, some oils hardly expand at all and others quite a lot. So with one oil I could check level after car has been standing overnight and compare it to running up to temp, then waiting 10 minutes for oil to drain and it would be pretty much the same level. But with different oil it could be barely minimum level cold and over max level when hot.
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  #18  
Old 7th September 2019, 05:24 PM
MikkiJayne MikkiJayne is offline
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There isn't a thermostat in the 5HP - it relies on the engine temperature. The 'oil cooler' in the radiator is really properly called a heat exchanger. It uses engine heat to warm up the transmission to 90*, and then dissipates heat generated by the gearbox in to the coolant once it's up to temperature.

The oil definitely does expand with temperature. The way I fill them is to top up to level when the gearbox is cold and then run it until 40*. It will drip oil while it is warming up as the oil expands, and then as soon as it hits 40 I put the plug in. Much easier to do it that way rather than wait until its at 40 then put fluid in, since its really easy to over-shoot the temperature like that.

As a side note, the 3.7 with the 5HP19 has an external thermostatic oil cooler in addition to the heat exchanger in the radiator, because the 5HP19 with a V8 on it is right at its operational limit so needs the extra cooling capacity. The 2.7TT and V8 Allroads have the same arrangement.
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