Sorry for such a dumb question but I bought my 4th boat and ive always ran mercury, but decided to try a Yamaha.
The motor is a 1997 Yamaha VMAX 150HP (Oil Injected & Carbed) OX66.
I filled the oil reservoir and then I took the cowling off and noticed an empty reservoir on the port side of the motor that's looks like it holds a quart of some kind of fluid. But mine is empty. What goes in here and should it be filled at all? Its bone dry.

Should be the oil reservoir under cowling....look for a switch next to empty reservoir and flip it to get oil from boat oil reservoir up to small reservoir under cowling.

So does it have to have oil in it?

if there is no oil in the tank on the side of the motor it could have been running w no oil. if there was no oil in the tank on the motor you should have got a horn I would see whats going on with that.

the previous owner wasn't mixing his gas, was he?

What oil res. did you fill?

Well, I think it is the oil reservoir for the engine and it uses a vaccuum to pull oil up from the main tank. If the previous owner was pre mixing oil and gas and did not tell you he needs to be horse whipped. I would think the engine would either beep or blow the first time out with no oil. I took my used Champion in last year when I bought it and had a full service done just so I was sure everything was in good shape.

Oil alarm should have been sounding off. These motors have a small in-line oil filter on the bottom corner of the main oil tank that causes problems if not changed regularly. Look at the wire running to the secondary reservoir to be sure previous owner did not disconnect the warning float. The oil system uses an electric pump to pump the oil to the secondary reservoir. http://www.boats.net/parts/search/Yamaha/Outboard/1997/150TJRV/OIL%20TANK/parts.html

I filled the oil reservoir that is next to the batteries. I will post a picture of the empty reservoir under the cowling

He never mentioned anything about pre mixing. I asked him about the empty reservoir and he told me to not mess with anything under the cowling. But I can't help the curiosity because I don't want my motor to have issues due to this reservoir being empty.

Looked back through the messages and he claims that its a 2nd oil reserve and if the motor runs out of oil it will use whats in that tank and only idle once that tank under the cowling is being used.
IM SO CONFUSED

The large oil reservoir in the boat pumps oil to the small reservoir under the cowling. It provides oil to your engine. If it has all been disconnected, then he was pre-mixing oil with fuel in fuel tank. Engine has to have oil for lubrication so you need to get your rig to someone who can inspect and verify before you damage the motor. Otherwise, you must add oil to your gas when fueling up.

that is wrong it has to be pumped into the tank on the side of the motor then to the oil pump below.you should have gotten a horn when it got to the second mark on the tank on the block.

You can take it to a local outboard mechanic and tell him you want to premix. He will disconnect the oil injection system. You will pour a pint of oil to every 6 gallons of gas after that. Peace of mind is worth something to me.

I just might go with the pre mixing ways. That's all ive ever had and I loved doing that. Simple. Any idea on cost of labor to remove oil injection?