Coming back from Autosport show on Saturday, left the car park and it was drizzling (that fine rain that soaks you through!) so put wipers on and washed screen. Had the air con on as usual. No matter how many times I washed and wiped, it stayed smeary. I just couldn't get rid of it. It stopped raining so I kept washing them but still no difference. The inside was clear and dry, all the smears were on the outside. Then suddenly after about 10 miles or so, it miraculously cleared all of a sudden. I have no idea why.

Weird. :confused:

Must have got some oily substance on the screen (possibly diesel), most likely picked up from the road from the car in front.