My 1988 740 Turbo (manual) with 185,000mi has a temperature sensative overdrive. Unlike most of the o/d problems listed in the FAQ, my o/d will not engage when the transmision is cold. Last winter (in the New England cold) the o/d would not engage until I drove on the highway for 10-15 minutes. All summer the o/d engaged no problem - but now that the nights are getting cold, the o/d is beginning to not engage until the transmission warms up. I replaced the relay last winter with no effect. When I atempt to engage the o/d in cold, no light, no click, nothing.

It seems that I may have to do one of the following: 1) change transmission fluid? - can this be done with a manual trans. - and should I use synthetic motor oil as some have, or ATF? 2) replace the solenoid? could be expensive

Any thoughts are greatly appreciated.

(By the way, I began using 89 Octane (mid-grade) instead of 87 (low) - the Turbo has much more "get up and go!" - I hope it doesn't hurt the engine/Turbo)