is using flushing oil acceptable in a t-15/d-20 combo?

Is it acceptable practice to flush a t-15/d-20 with 20 or 30 straight weight, statically, and letting it dump out before gl-4 refill? or does it serve little advantage?

these units likely had original oil when I drained them. No scary metal on magnets and oil wasn't the 'Nevada Silver Mine', but it was yucky. 44k miles.

Or am I am better off simply filling with GL-4 and running a bit then doing a another change with a nice hot drivetrain say in the summer?

 

I vote for option B. You are not getting enything else out of the case by doing a static flush. If there was no metal and the oil did not look like milk shake then you should be good.

 

there was a bit of moisture, ok water, but far from milkshake for the likely age of the oil.

I'm agreeing. I will refill, give it a couple months then change it after a run again in the hot part of summer.

 

Flush is pretty pointless honestly. Just remember to continually check the level of the trans for a while after initial fill since the oil tends to migrate into the transfer case.

 

thanks, going to fill with GL-4 in both units and check level regularly, then plan on a nice summer day change after a drive to get a dump out while it's hot. I have like 3 gallons gl-4 stashed so no biggie.