ZF 6HP19A tiptronic gearbox (A6 3.0 TDI Quattro)

[Pitzury]

Trans cooler Audi A6 endtank.jpgTrans cooler Audi A6.jpg
I am surprised nobody has anything to say about engine and trans cooling on our cars. Nobody else believes fans should turn on a lot sooner than 105*C?

The pictures show how tiny and inefficient the factory cooler is. It will be good for power steering on my car soon.
Another problem with these, especially with cheap aftermarket ones is trans fluid mixing with coolant. That's one of the leading causes of failures on these transmissions,

[54A4Avant]

I agree it sounds odd if trans fluid is reaching 105C, but don’t know enough about it to really comment. How much of the trans fluid reaches this temperature before the cooling begins, is it just a small proportion or a large part of the volume of the fluid? It must surely shorten the lifespan of the fluid, which does not sit well with Audi’s “sealed for life” claim (short life!)

[54A4Avant]

<snip>
So I would replace the valve body seal because it is not that expensive, run the engine until about 4 litres would go through and than stop and go ahead install the filter and pan and follow the factory fill procedure.

As far as catching the flushed fluid, I would use the a clear plastic bag secured to the transmission and reduced down to a smaller hole where the feed hose go through

Thanks for your advice Pitzury.

[Pitzury]

I agree it sounds odd if trans fluid is reaching 105C, but don’t know enough about it to really comment. How much of the trans fluid reaches this temperature before the cooling begins, is it just a small proportion or a large part of the volume of the fluid? It must surely shorten the lifespan of the fluid, which does not sit well with Audi’s “sealed for life” claim (short life!)

The temperature reading is in the oil pan so most of the fluid is over 100*C. However the fluid heated 10-20*C more in the torque converter when unlocked in slow traffic, hill climbing or towing will raise the fluid temperature even more. And the tiny trans heat exchanger in the front radiator cannot deal with that.

Therefore I will go ahead with my plan to modify the trans cooling system by adding a A8 water/oil heater and an external Setrab air/oil cooler. Just trying to squeeze in the right side of the transmission a Magnom magnetic filter, an external WIX 57819 filter http://www.wixfilters.com/Lookup/Par...x?Part=1824060 and an inline remote thermostat. These pictures can give you an idea.
Trans fluid cooling.jpg
Trans fluid warmup.jpgTrans fluid temp control.jpg

[54A4Avant]

Wow... it will be interesting to see the results, as I presume you’ll be evaluating the change in temperatures and performance. It’s far beyond what I would ever take on, but I guess you have lots of experience with systems of this type. Very interesting however and I’m surprised the OE setup allows the fluid to get so warm. No wonder ZF are screaming to ignore the Audi “sealed for life” message. I wish I’d known more about this whole issue and changed my trans fluid three years ago, before my TC lockup clutch slip began. Maybe I would have prevented the issue entirely.

[Pitzury]

I don't expect spectacular results and noticeable changes with my warm-up/cooling plans other than getting faster to about 70*C and staying there or at less than 80-85*C hopefully at all times. In my experience with both 5HP19 and 6HP19 transmissions they perform best above 60*C and under about 80*C.

As far as your TCC slipping you need to see what your solenoid N371 is doing and what the result in slipping is. Also check what the N233 amperage is when the slipping is happening. N371 is regulating the closing or opening the TCC together with reversing the flow through the converter. N233 amperage will give you and idea of any compensation for wear or leakage is attempted. Read SSP_283, SSP_284 and SSP_385 to better understand how things work.TC Open-Close.jpg

[Pitzury]

Trans fluid warmup step1 completed. I installed an external Perma-Cool 1070 remote mount thermostat and an inline Magnefine magnetic filter on the return line before entering the transmission.
Trans fluid warmup step 1.1.jpg
I had enough of seeing cold trans fluid temps. No more than 60*C at highway speeds and getting up to about 45-50*C very slowly in normal city driving with engine coolant radiator return temps below 18*C. The tinny trans cooler copper pipe is in the cold end tank of the front radiator. I also reversed the lines going to this cooler having now inlet in the lower part and outlet in the upper one.
Drove the car this weekend to test it and check for leaks before the 2200 km drive in the next week. Now temps are getting consistently up to 74*C and staying between 70-75*C once up there. The temps are climbing faster but still about 20-30*C slower than engine coolant so the next step is installing the water/oil heater that I have from a A8 3.0TDI.
I have to run now but I will get back with a description of the parts and labor involved.

[Pitzury]

Drove 1100 km yesterday and, at motorway speeds in 8*C ambient, trans fluid temps stay in the sixties but closer to 60*C or right at 60*C. I knew step1.1 with only the thermostat install without the A8 warmer will not make me happy because of slow temp rise but I did hope to get to the seventies eventually. It looks like that these transmissions are like a heat pump and cannot get up to temps when the TCC stays locked all the time. Engine coolant and engine oil were around 80-84*C, coolant return from the radiator was in the teens 12-15*C.
To be honest, I don't understand how was the trans fluid getting up to 60*C before when it was not bypassing the coolant radiator which has the cold end tank at such low temperature. There has to be some sort of cooling flow regulation up to about 60*C done by the mechatronic. The lubrication valve could limit the flow to the cooler but I don't know how.

Back to my plans, I will install the A8 4E0317021E water/oil cooler/warmer on the line that bypasses the OE cooler by the external thermostat as soon as I get back home. And later in spring I will install a Setrab 915 external cooler and use the OE cooler for the power steering system.

As far as the parts and labor needed: do not start this unless you are willing to use a big crowbar to bend things out of the way. I used the cooler lines 4E0317818L FEED 4E0317817L RETURN that go up and over the trans to the A8 3.0TDI cooler 4E0317021E and 4E0317827AB bracket location but, in Audi's endless wisdom, they installed on the A6 a cat converter with a support bracket mounted on the transmission that is in the way of the cooling return pipe. So this is where you need to bend the support bracket out of the way but also the cooling pipe somewhat. For now I left the better part of the rubber part of these lines where I attached the thermostat and Magnefine return filter. The rest of the lines were socketless 8AN hose and fittings except the two Metric 60* 18x1.5 fittings, male and female used to connect to the lines on the front radiator. I will take some pictures before taking things apart.

[Pitzury]

Did some more testing with this new setup and learned interesting things.First thing is that the external thermostat/cooler bypass valve does help warming up the trans faster than before. When I left Villach, Austria, it took 100 km on the motorway to get the trans temp up to 60*C going 130 km/h with a few 100 km/h speed limits through tunnels.


But back home in negative ambient and more TC Clutch slipping the temps were getting up to 45-50*C faster than before the thermostat install. Yesterday it was about -4*C ambient and I drove to the city. I live next to a country road going to the city with a 90 km/h speed limit. I reach the city limits in 8 km and yesterday, with no traffic, I got there with engine temp at 55*C, coolant return from the radiator 0*C, engine oil temp at 40*C and trans temp at 25*C. Then I drove another 4 km at lower speeds, stop and go traffic and reached the destination with the engine at 60*C, engine oil at 50*C and trans at 45*C. Further driving in the city got the trans over 65*C but than it went down to 60*C on the way home outside the city.


One very important note to mention is what the trans temperature has to be for the software to allow the TCC to be locked, at least on my 2011 3.0 TDI. SSP's were saying 40*C which I new it was false because I could lock the TC in 600 m of driving to the city before. Well, this time, the trans started below 0*C and locked/regulated the TC Clutch only after getting over 10*C.


Another thing to mention is that the trans adaptations changed before the long trip and I believe the trans adjust the adaptations more when the trans temperatures are getting closer to 80*C so that's another benefit of warming up the fluid in the winter.


I am looking forward to install the heater but I will do it together with the external WIX 57282 filter and the MAGNOM magnetic pre-filter install. Parts are coming at the end of Jan and I hope to have enough room for the remote filter install.

I don't know were and how to install the trans oil temperature and fluid pressure gauges I plan to use so any recommendations are appreciated.

[Pitzury]

WK AUF plug.jpg
I believe the WK AUF plug location is where the red circle is. I will try to see if there is a way to plug the galley towards the Torque Converter valve. But I am thinking that there may be another way to my method of flushing the converter without wasting the fluid that goes to the sump. What if, before pushing fluid through the WK AUF plug, I remove the valve body and replace the seals, re-install the pan and filter and then start pushing fluid? Would the clean fluid that goes to the valve body go in the pan without mixing with old fluid and the old fluid from the converter would go out the cooling path and not through the valve body towards the oil pan?