Mixing mineral and synthetic ATF in a tranny?

[AuH2O]

I'm installing a new pan on my 700R4 and in the process am planning on going from mineral Dexron III ATF to synthetic (Red Line D4 to be exact). Since with a normal drain I'd only get about half the old oil out of the tranny, I'd be driving around with 50% synthetic and 50% mineral ATF. The latter percentage will of course drop over time, but with regular oil change intervals I'm still a long way off from reaching 100% synthetic.

I'm a little cautious about complete trans flushes; but do I need to be? Or should I flush it until it's all Red Line? Other than flushing I don't see how I would achieve a complete drain of the transmission short of pulling it apart... Would there be any other disadvantage to driving around with a 50/50 mix other than that I wouldn't get the full range of the supposed benefits of the synthetic D4 in as high a degree than as if I'd done a complete drain? Would there be any compability issues with the oils not mixing properly? (I wouldn't think...?)

 

[yelarat]

If the trans is high mileage and has not had routine flushing i would discourage you from flushing. The flushing process pushes fluid though the trans in 2 directions one being the normal flow of fluid the other is the opposing direction, this action does remove build up, but at the same time it can loosen buildup which has the possibility to break loose later, at unexpected times....like in B.F.E. This can cause an trans failure and all the joys of getting you and your rig back to civilization .

 

[yelarat]

ray

 

[xtrmjoe]

I am sure the Red line would not reccomend it. I have done it befeore and not had any issues. I know they would say not to do it on engines either but they do make blends that are that right out of the bottle. You just have to make sure that all the detergents and additive are compatibile.

 

[AuH2O]

Yeah, I get what you're saying about trans flushing, and I'd rather not do it. I mailed RedLine and got a generic response along the lines of what I had envisioned they'd say:

Thank you for contacting Red Line Oil, the D4ATF is compatible and will mix with other ATFs including petroleum products. There wouldn't be any disadvantage to the mixture and with each successive change a higher percentage of D4 would be in the system.

So I guess I'll just do as I initially intended.

 

[tumbleweed1002]

I do trans flushes and filter changes at the shop at work if you just do a filter change only about 2 to 3 qts will be left in the tranny (what ever the capacity of the converter) but you would be much better off not flushing the syst. you can change the fluid again in about a week or so and upon refilling you would be in the area of 95-98% pure syn.