ZF 6HP19A tiptronic gearbox (A6 3.0 TDI Quattro)

[Pitzury]

I am testing the transmission temperatures and I can understand why the transmissions on these cars can have the fluid in great shape after so many km: most of the times the temperatures are low or in the eighties Celsius. Maybe too slow warming up if you drive outside of a city in the first km. But I discovered something I don't like at all. If you drive the car in slow city driving WITHOUT A/C on, the coolant and engine oil can go above 100*C and so does the trans fluid. In 20*C ambient and less than 50 km/h driving the coolant went up to 105*C, engine oil and trans fluid just above 100*C. I believe channel 098 in the engine measuring blocks reads radiator coolant return temperature and it was around 100*C in these conditions. NO FANS ON at these temperatures. That's weird in my book.I am told the fans will come on above 110*C only which does not make any sense to me. If there is a sensor on the radiator outlet than it must be taken into consideration for activating the fans at slow traffic. But even if the return temp is over 100*C the fans do not turn on. Obviously the trans at this time cannot be under 100*C. I believe coolant and engine oil above 100*C is not something wrong but trans fluid at 100*C or above is not what I would like to see. At that kind of temperature the transmission is not as smooth as it is a 80*C.
Do you guys think this is normal on our cars?

[Pitzury]

I was told by my former service tech to power wash the condenser and coolant radiator since they are dirty and full of debris. He said that he had several similar cars with overheating or A/C turning off after a while in slow traffic, problems solved with cleaning of the condenser and radiator. I sprayed engine cleaner wherever I could,drove the car about 1 km at 60-80 km/h to get the motor solvent deeper and then started rinsing. At first I used low water pressure without turning on the power washer and then turned on the washer. A lot of dirt did come out so I took my time until clean water was draining.
Things did change dramatically. Coolant out temperature dropped a lot and so did the rest of the temperatures. I drove 160 km in 12*C ambient and engine oil and coolant were in the eighties and transmission at 58-62*C at 100 km/h driving. The coolant radiator out was at low twenties and climbing only when stopping or very slow traffic in towns.
Hopefully we will get some warmer days to drive it in the city.

It looks like I was able to bring things back to factory specs but I still have an issue with the fans software. Efficient or not the coolant radiator can reach higher than 100*C and that will overheat the transmission fluid. How hard would have been to program at the factory to switch on the fans when the transmission fluid goes over 85*C for instance? And why not turning the fans on when coolant is over 95*C AND return over 80*C? I would like that to be done and I wonder if tuning companies are doing or can do something like that.

Next time it is warm outside I will test again.

[54A4Avant]

Doesn’t sound great to me, especially with a “sealed for life, never needs new transmission fluid” system as Audi would have you believe. Interesting to hear about the difference washing the radiator made. Makes sense really, but basic maintenance like this is easily overlooked.

[Pitzury]

I am glad I cleaned the radiators because it made a big difference. I got to drive the car in the city and outlet temperatures stay under 20*C until coolant gets higher the 82*C. This is in 11-13*C ambient. Than it goes up some (30-50*C} especially if there is very slow traffic but drops fast as soon as the car moves. Highest I could get was when I let the car idle until coolant got up to 90*C and radiator outlet to 88*C. At this time transmission was at 84*C. No fans on obviously.
I have two other project cars with auto transmissions that I am working on and posting my findings:
1999 2.5 TDI T4 Caravelle postings here 2.5 TDI auto box overheating? - VW T4 Forum - VW T5 Forum and
2002 1.9 TDI Passat postings here 01V 5HP19 additional trans filter, thermostat and cooler | Volkswagen Passat Forum
In the Passat thread I am talking about cooling/heating the trans fluid and I plan to do it on the A6 also.

I noticed the 6HP and 5HP transmissions on my cars have the same setup: lines to the coolant radiator with no inline thermostat. I live 10 km from the city and both cars behave the same warming up. Both transmissions lockup -the converter early and produce little heat and , by the time I reach the city limits, the coolant is at 70-80*C, engine oil at 60*C and transmission under 40*C.
So here is my question: Is the most part of the fluid diverted from cooling at warmup up to about 60*C? I found hard to believe trans fluid can warm up if the coolant temperature in the radiator is under 20*C. Installing an inline oil thermostat on the Passat did not dramatically changed warmup times and that is why I plan to use the A6 water/oil heat exchanger to warm the fluid faster. Both transmissions seem to go up to about 60*C slowly and then tend to stay there unless coolant in the radiator gets warmer the 60*C. So is the trans fluid flow through the cooler regulated up to about 60*C?

[Pitzury]

I had the car tested and I am sad to say everything is working in the cooling system. Unfortunately it is working the way the factory intended and I don't like that.
Fans turn on only starting 105-106*C at low speed. Above that the speed gradually climbs to high speed above 110*C. Unless you activate and keep the engine oil temperature display on, there is no way to know when engine temperature goes that high because the OE engine temperature gauge stays right around 90 between 80-105*C.

The radiator return temperature sensor G83 is on the pipe going to the EGR cooler and it doesn't seem to be used for engine cooling. It is probably only used in the EGR cooling.

So what do I do now? Like I said: engine oil over 100*C is desired but not so for the transmission fluid. So we have a conflict of interests which means that, if we want the trans fluid to stay below 80*C at all times while the engine oil can get above 100*C, we need to stop using the factory water cooler and install an external air/oil cooler with fluid flow thermostatically controlled to this cooler. Factory trans cooler in the radiator can be converted to a power steering cooler. And to warm up the trans fluid faster install a water/oil cooler in the short cooling circuit somewhere in the lines where the engine coolant G62 temp sensor is.

[Pitzury]

I did some more research to find out why my method of replacing the fluid out of the converter differed from the 2008 2.0 BMW X3 awd and the 2011 A6 3.0 TDI I have. There was so much more fluid going through the cooler line in the BMW compared to the Audi andd I believe one reason is that flow through the cooler is restricted on the Audi to help warm-up. I see that both in my test drives and in this chart.



Plus if you look at this picture you can tell flow goes back to the valve body before leaving the trans to be cooled.



More info here about the WK AUF port I used to replace the fluid in the converter.
Sonnax Six Ways from Sunday: Diagnosing ZF6 & Ford 6R60/80 TC-Related Drivability Concerns

[54A4Avant]

That’s some interesting stuff Pitzury, where did you find the schematic image you posted? I’d be interested in looking at a similar diagram for TCC control, to see which valves might be involved so I can pursue my torque converter lockup clutch slip problem.

The linked article is a good read, although a bit hard to follow for a non specialist. I did notice he mentioned blown engine mounts as a possible cause of lockup clutch slip, which is interesting as my car has had an N145 right side engine mount code for years, but I never fixed it because of I heard these engine mounts don’t cause problems when failed. I’m struggling to see the connection between engine mount and TC clutch slip, unless there is wear in the transmission bushings resulting from excess vertical physical movement because of an engine mount. Seems tenuous.

[Pitzury]

I have several pdf files I use for research that I downloaded to my computer.

The mentioned blown engine mounts are a possible cause of rough idle in reverse not the lockup clutch slip.

[54A4Avant]

Ok got it, thanks. I’ve decided I’ll go ahead with changing fluid and filter as a first step and then see how my transmission behaves after that. If I later need to remove valve body and go changing solenoids or replacing valves within it, then that will come later.

I’ve more or less ruled out the possibility that my problem might be down to the rubber seals above the valve body, so will be leaving these alone.

[Pitzury]

When I came across these guys Transmission Service in Ventura, CA | Dave Wilkes Transmission I was happy to see I am not the only crazy guy out there to think that the best way to really FLUSH the transmission is feeding fresh fluid directly to the fluid pick-up tube . Then I see tomcoo efforts on the jaguar forum https://www.************.com/forum/xj-xj6-xj8-xjr-x350-x358-28/zf-6hp26-transmission-fluid-flush-diy-217150/page3/ post #53 and I believe it is not that difficult to do.
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