in the oil
You have an oil leak.
The Buick needs 5qts of SAE 5W-30.
The 1989 Buick Century oil sender is located inside of the oil pan. You will need to remove the oil pan in order to view the oil sender.
You didn't mention the year of the Buick but, look in the glove compartment for the oil life reset switch.
i would recommend eBay
2
The oil capacity for a 1991 Buick Century 3.3 is approximately 5 quarts. The recommended oil type is 10 W 30.
Do I have to pull the motor to change the oil pan gasket on my 1985 buick rivieria?
Bottom of the oil pan.
inside your oil pan
The 1992 Buick oil sending unit can be found on the left-hand side of the engine. The oil sending unit will be a few inches above the oil pan.