Understanding ATF specs/viscosity (ZF 6sp effects)

[Spoony]

Hi everyone, my first post here, seems a great knowledge base so hopefully I can learn something.

I have an Australian Ford XR6 Turbo with 4.0L turbo with 300rwkw and quite a lot of torque (mild mods).

It runs the ZF 6HP26 6sp auto. I've noticed it flaring/slipping under full power/speed shifting 3-4th gear. All other gears are fine etc (well I can't really test 4-5, 5-6th as I'm already well into go to jail territory haha)

I'm not sure how long it has been like this as I don't often do these kinds of speeds, but i'd say its a fairly recent development. Cold 5deg night temps have seen the car going faster, so making more HP, perhaps highlighting the issue.

The trans fluid currently in it is a local product Nulon Full Syth, not recommended (what aftermarket fluid is in these boxes), but looking at the specs should be OK. From what I've read Mercon SP is what Ford specs for these which Nulon & Gulf list in their specs (not Castrol Transmax z though). However what is 'recommened' seems to depend on the manufacturer/country etc.
Also a local trans shop uses it in these boxes without issues, in taxi's etc (mind you they have less HP).

Now I'm considering it's just the increased torque + hp that the box is struggling with.

I have read of people having this on the stock ZF fluid, and changing fluids with good results.

Another local oil supply has recommended their fluid Gulf Western SynTrans in the ZF 6sp and said it works correctly and has the required additives etc.

Basically what I'm trying to understand is what the difference specs in these fluids mean and what effect they have in a clutch based auto such as the ZF 6sp.

From the below info I'm reading the Nulon is the thinest/weakest product with regards to thermal viscosity etc. The Gulf Western product is the highest.

Does anyone know as such will this aid with more positive/stronger shifts? I don't have the matching specs fro the original fluid but I think it is thinner again.
I guess also comes down to what kind of friction modifier etc are in the mix and how the clutch plates react to these?

Nulon Full Syth
KV @ 100°C, cSt 7.000
KV @ 40°C, cSt 33.40
Viscosity Index 179
Density @ 15°C, g/mL 0.8514
Pour Point, °C -45

Castrol Transmax Z
KV @ 100°C, cSt 7.1
KV @ 40°C, cSt 36
Viscosity Index 170
Density @ 15°C, g/mL 0.836
Pour Point, °C -60

and the product that has been recommended by the supplier & I'm considering flushing in.

Gulf Western SynTrans
KV @ 100°C, cSt 8.5
KV @ 40°C, cSt 40
Viscosity Index 200
Density @ 15°C, g/mL 0.8462
Pour Point, °C -42

As you can see it seems to have higher viscosity(stablity?) at temp etc.

Cheers for taking the time to read all that

Dan.

 

[Steve S]

I am not sure how oil selection would help the slipping from what seems to be too much power through the tranny? Is that a weak point in the trans?

 

[Spoony]

It seems to be a bit of a lotto but qutie alot of people have run another 50 to near 100rwkw more than I have through the same box ok.

However some that did have flairing noticed different oils fixed this. Transmax Z being the most commonly used.

It seems very close in 'spec' to the Nulon product, however there are unknown friction modifiers and aditives that perhaps come into play?

Also from what I have read the ZF fluid has a lower viscosity than all of them by 10-15% vs the Transmax Z. But as above viscosity along perhaps is not the only factor?

The Gulf Western product has a noticeably higher viscocity than the others and genuine, so would expect it to behave different. Generally from what I have learned with autos higher vicosity provides firmer shifts. Not sure why though, higher fluid pressure?