'93 3.0L Taurus

When it warms up, (actually, after the engine has been up to operating temp for 10-15 minutes or so) it seems to drop out of gear at stop lights, but only when in overdrive. This does not happen in 'D'

In other words, what it should be doing at a stop is shifting from a higher gear to first gear, but it is apparently shifting to neutral. Then, it won't go into any forward gear, unless I first shift it to R, and wait a moment for it to engage, then shift to D or OD. If I then put it into OD, it runs great until the next stop. If I put it in D, it runs all day, and the problem never happens.

A couple of other clues: I just bought this car, and it was highly overfilled with transmission fluid, about a quart over. Also, the radiator had just been changed the day before I bought it. (History of overheating the tranny?)

The previous owners claim they never had this problem. If so, it may have been caused during the radiator change, maybe they accidentally messed up a vacuum line or ... I don't know what.

Any help before I take it to the shop?

Usually a guy that buys a '93 Taurus doesn't have a lot of spare bags of money lying around to pay mechanic bills, if it can be avoided.
Thank you,
Chris

 

Check the filter. it may have come loose or was improperly installed. My $.02 Rich