have read this site for long time and got a lot of usefull info.now I have specific question.a 1988 tcm 850 wheel loader. transmission is 4 speed powershift with torque converter.have always put utf in it.just got owners book, it says 10w engine oil for trans/converter.what should I run.the whole book seems old spec.engine oil says 10w winter,30w summer.i run 15/40.am thinking of change to 5/40 t6 or 10/30 t5 to help cold starting.would this be too thin for old sloppy engine in summer.trying to keep alive cause cant get parts,{any info on that},cant afford to replace.thank you for any info.