[Agent WD-40]

I did a complete flush of my automatic transmission fluid at 30k miles. I replaced the stock fluid with 15 quarts of Mobile 1 synthetic transmission fluid. I'm now coming up on 75k miles on my truck. Should I replace the fluid again?

I have only towed only 3 times since I replaced my fluid at 30k and the trailer probably didn't weight more than 3,000 LBS. The majority of my driving is city but lately I have been doing more freeway miles (probably 70% city, 30% highway- as of the last 3 months this has reversed). I go off road with my truck about as often as I tow. Can I push my drain to 100k miles?

 

[Matador98]

I think a full swap is overkill. I think you could push it to 100K no problem, but to be overly cautious, I would do a swap and refill in about 15K (at 90K) which is a 60K drain and refill interfal. I think that would be fine. But if you want to do something now no matter what, a drain and refill would be more than enough.

 

[Hugemoose]

I think a simple 4 quart drain and fill would be fine. The fluid you have now is most likely completely fine but it surely isn't a bad thing to drain and fill. A full flush is probably overkill though...

 

[Imdone]

I didn't do a flush til I was at 90k miles. I did the trany fluid replace at 30k and 60k though. Flush was well worth the price at 90k miles though. I could absolutely tell the difference.

 

[trog55]

FWIW, I'll throw in my experience...

I did a complete flush and refill with Mobil 1 synthetic at 26,300 miles. After almost 75,000 miles, 4-1/2 years, some moderate to heavy loads and towing, I did another complete flush and refill, this time with AMSOIL ATF. The Mobil 1 that came out was still a nice red color, not quite as bright as the new AMSOIL but still pretty, no odor, no detectable gritty feel to it. I nearly felt like I had wasted my time and money changing it then instead of waiting a while longer but i figured it was time.

In my, very humble, not-a-mechanic, opinion, with only 40,000 miles on your present Mobil 1, I think you're still pretty safe with it. Wait till you hit (at least) 100,000 miles (70,000 on the ATF) and then splurge!

 

[2000LtdKen]

Trog,

Any noticeable difference between Mobil 1 and Amsoil in the tranny? My truck has 145k on it and the last 60k miles with Schaffers Semi Syn.

Thanks,

Ken