Since it has gotten cold this year, when my truck sits over night or a period of time of a couple hours or more my oil pressure guage won't move when I start it. But the weird thing is when I shut it off right away and start it again it's fine. I thought the oil pressure sending unit was bad but if that was the case it would do it when it's warm out as well. It did it to me once or twice last winter as well, but not in the summer, only when it's cold out. The sending doesn't have time to warm to start working, cause like I said i'll shut it down and start again immediately and all is well. Any ideas?