The answer depends.
1 Liter of Oil, can be a count noun. If it is placed on a container, it can be a count noun. Imagine that you have many bottles containing 1 Liter of Oil. Can you count it? Yes. You can.
1 Liter of Oil, can be a mass noun. If it is not placed on a container, it can be a mass noun. Imagine 1 Liter of Oil scattered on the floor, can you count it? No. Can you define that it is 1 Liter? No.
But since you do not mention any container, the answer is no, it is not a count noun.
