my dads 99 auto 4runner did the same thing, but the radiator cracked internally and the ATF mixed with the coolant and buggered everything up. a new rad and $1300 later, its like new again.... (lots and lots of labour to get all the oil/coolant out)

89 4Runner
3" BL, M/T locks, 33"bfg mt, bilstein, Kayline, tubebumper, toyotafiberglass panels
TBI: Elocker,3.4 w/ORS,b+b,S2Sstg2cams,arias pistons,P+P intake,TRDs/c,URDpullies+7th,downey headers,MAPECU2,WEGO WB, SupraMAF,walboro255,stg4clutch, EPaOo2 sim