I am using Mobil 1 5w-30, will the lower weight make the oil pressure go down? Before, I was using 10w-30 and never had this problem. Normally when the car gets warm, it will be sitting at idle and the oil pressure light will come on. It has never came on while ive been driving.

Mark, a 5W-30 and 10W-30 should be almost identical

in viscosity when both are warmed-up....

There is something that I have found when Mobil 1 is

used for the first time....

For some reason (don't ask why) for the first oil change

or possibly even two changes, there is a temporary

increase in oil consumption....

So, if you are just starting to use Mobil 1, be sure to

check that oil level often....

Here's hoping you just need to add some oil....

Synthetic 5W-30 will flow easier than standard 10W-30. This will cause a small drop in pressure on most engines. Your pressure light was probably just above the point of lighting with the 10W-30, so the small drop was just enough to light it at idle (at idle, oil pressures are the lowest). I wouldn't worry about it unless the light starts coming on at higher RPMs.