My 97 Prelude is overheating after 10 minutes of either being idle or while driving.

I checked the radiator resevoir and it looks like there's fluid inside up to the middle.
I checked the oil cap and I think there's a slight milkyness in one spot. But when I look into the oil hole with a flash light it just looks like regular oil.
My car is not omitting white smoke but it does smell more smokey then before.
When I turn the car on with the radiator cap off I do see some steam coming out but then it goes away for a while.
A couple weeks back I changed the thermostat because it was overheating on me but it ran fine for about a week or two.

I took the car to a smog place the other day and they told me the system is running lean..

Anyone?

 

hummm...not sure..but i would like to know.

 

Oops, low on radiator fluid!

I thought there was fluid because the resevoir is like half full. But I put water in and it stopped overheating.. I think it might be leaking but I can't find where! There's nothing on the floor!