ZF 6HP19A tiptronic gearbox (A6 3.0 TDI Quattro)

[Pitzury]

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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.
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I believe the trans fluid is warming up even though it goes through a very cold radiator because there is no flow of coolant through it before the coolant thermostat opens so I don't think flow to the cooler is regulated when cold.
Changed the plans for the cooler choice. I will use Setrab 625 cooler for the trans and bolt it together with a 610 cooler for the power steering and a 9"Spal fan. Also plan to use the original steel cooling lines with adapters to 1/2"AN hoses to install the filters and thermostat. BTW I decided to build my own thermostat and will post some pictures when ready.
Since there is no warm-up help for the transmission I plan to go ahead with installing the A8 4E0317021E but I wonder if anybody heard about one of these coolers failing and mixing coolant with trans fluid. I've seen similar coolers made by KTM for Ford which failed and mixed coolant with trans fluid but could not find one of these A8 KTM coolers failure story? It would be stupid to have my quest for improvement lead to a catastrophic failure because of this cooler/warmer.

[Pitzury]

I’m so disappointed because I tested the 2 A8 coolers I have and one has a leak between oil and coolant. One is a 2004 and the other is a 2007. The 2004 had cleaner fluid in it than the 2007 yet the 2007 is leaking.
I planned to use these for warmup on the Passat and the A6 but now I am afraid to use the good one since it can go bad later.
My 2 year old plans are screwed. Don’t know what to do.