Depending on driving conditions your safest bet will be 5w30 multigrade oil,the numbers represent oil grade or viscosity (thickness)there are many types of oils which u may research that may be benificial to your engine depending on mileage and how the vehicle has been maintained (additives,seal conditioners etc. and soforth )
5w-30 or 10w-30.
2002 Montana holds 4.25 Litres including the oil filter.
first suggestion would be the head gasket which Montana's are notorious for having problems with, followed closely by a crack in your cylinder head or engine block
You can find the oil pressure sensor for your 1999 Pontiac Montana on the front of the engine. The low pressure oil sensor will be just below the left cylinder head.
right next to the oil filter.
4.5 quarts of 5W-30
No problem, if it's like my 2001 Montana. Just press your mileage trip button until you get to the 'oil' reading. Then, just press on same button and hold for a few seconds. It should go back to 100 (fresh oil).
5w30
Bottom of the engine on the oil pan.
open the hood and look straight down, the port is right next to the a/c pump it usually has a blue cap on it that screws off.
you must remove the front suspention crossmember and suspension.
Approxiamtely 4 litres.