What could cause an low oil pressure after oil change? I had a friend of mine change the oil in peggy and since then shes been throwing the low oil pressure, as i continue to drive after 10 mins or so it builds up. the only thing that was different is i used the high mileage 10-40 oil.

The oil pressure sensor is notorious for going bad on the 3.8 engine. I would replace it and see if that fixes the problem.

assuming you verified the level is good. high mileage oil is no good. i tried to run it in a couple of my cars and it acted like i had 2 month old gas in it the whole time.

I have high mileage oil in my LeSabre (163k miles), and it runs fine...

maybe it depends what kind, i use regular valvoline changed every 5k, i had probably 180 when i tried valvoline high mileage on my bonnie and it ran pretty rough, but i dont think it lost mileage. had maybe 160 when i tried it on my old 03 monte and that lost some mileage and ran rough as heck till i changed it back

I'm running Mobil1 Super 10w30 high mileage formula, seems like a quality brand at a good price when I changed my oil a couple months ago. Although I don't really think there are too many considerable differences between oil brands these days (when comparing equal weights).

To the OP, I though most 3800-II'* suggested 10w30... does yours specify 10w40?

it recommends 10-30 for my engine

Why did you use 10w40? Technically that is a bit heavier/thicker than 10w30. Slower moving oil, which it would be on start-up before the oil gets hot, may be tripping a low pressure sensor.

Generally I'd say stick with manufacturer recommendations on fluids, unless there is a real compelling reason to switch to something else.

you are right but the second number is operating temp rating so it would be the same at start up and too thick at operating temp

could it cause damage to the engine?