Mixing synthetic 3309 ATF with Mobil 3309.

[Sardine]

My car AW55-50SN is currently on Mobil JWS 3309. Can I do a simple drain and fill (one drain and fill only) with Nulon synthetic ATF, thus mixing the two type of ATF, synthetic and non-synthetic ATF?

[difflock54]

As far as i am aware mixing synthetic ATF with non-synthetic is not recommended.

[jimmy57]

No, the two will mix fine. I have drained and filled several gearboxes with synthetic when the original fluid was not synthetic. Years back there were rare incompatibility issues but those were when the engine or gearbox was very cruddy to begin with and the synthetic had a higher solvent action to knock the sludge loose. The base stock petroleum used for ATF and engine oil is pretty close to synthetic.

From Valvoline:
Automatic Transmission Fluid FAQ

I had my vehicle's transmission fluid changed using Valvoline MaxLife™ ATF Fully Synthetic. Conventional transmission fluid was used for all previous changes. Will this cause a problem?

No. Switching to synthetic transmission fluid after using a conventional product will not cause a problem. Synthetic and conventional oils are 100 percent compatible.

[Georgeandkira]

It'll be fine.
On the shelf I've had genuine Mobil 3309, Valvoline MaxLife Dex/Merc-Mercon LV, Aisin T-IV, Wolf's Head Super Universal Synthetic Transmission Fluid and genuine-branded Toyota T-IV. I would grab 'em randomly when servicing the 5 55-50's in the family.

1,3 and 5 are conventional. 2 and 4 are synthetics.

They worked together well.

[abscate]

I think the only ones that have compatability issues are Shell and Mobil products..

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[Sardine]

Thanks all.
I'll have a go. If bad things happened I can always do a full flush to recover.