I have a 90 4runner, 4" lift 3.0l a340h tranny..... Ok, i was on the freeway at higher speeds. All of a sudden there was smoke everywhere, i freaked, pulled off quick to the shade (it was 90+ outside) I checked under the truck and there was fluid from the tranny back scattered, i assumed it was oil, but the truck was running great and i couldn't tell right away where it was coming from. i drove to a gas station and turned it off, got under and cleaned it all up, the oil was a lil low, topped it off and started it up, no leaking anywhere, drove i a few blocks to friends house and let it sit, drove home that night and not a drop of fluid. The next day got out underneath it and the fluid that showed was red. I cleaned EVERYTHING under ther and drove it around for a bit, including on the freeway, still not fluid anywhere. I was going to change my tranny filter and gasket anyway. So, i've drained my fluid and pulled the pan and filter. The fluid was red for a minute then brown and nasty. I don't think its ever been changed. Just about to put it back together but i was wondering, is there a pressure relief valve anywhere on the tranny?

 

i noticed my tranny cooler has bunch of mud caked into it and i'm cleaning that as well

 

Trans overheated,fluid boiled and foamed,and blew out the vent.Change the fluid and add lube guard to the trans.