how to find a leak

How do you find a leak? The sentra I have has a leak. I'm pretty sure its oil. I put some cardboard underneath so I can see what color it is. I never see any smoke while the engine is running so I don't think the engine is burning the oil, just leaking. Is the oil pan very hard to get off?

You should really post this over in one of the Nissan forums on this message board that pertains to your car, you are more likely to get help there than over here in this generic forum.

Suggestion of things to post:
- Which model of Sentra.
- Year of car.
- Engine size (i.e. 1.6; 1.8; 2.0; etc.).
- Miles on the odometer.
- Which side of the engine it seems to be coming from in relation to the car (i.e. front, back, driver's side, passenger side).
- How big of a leak.
- Has it gotten worse over time.
- Anything else that you think may be important.

And from the technical side of your basic question, you can purchase a UV dye leak detection kit for relatively cheap these days from some of the auto parts stores. You put a metered amount of dye, based on the crankcase capacity, into the oil, drive it for a short time (depends a bit on the size of the leak), then use an Ultra-violet (ie: 'black') light which will cause the UV dye and the leak to glow.

Have you checked other fluids to make sure they are not low, such as the power steering fluid, the transmission fluid, and the brake fluid? The color of the cardboard makes it difficult to determine if what's leaking is brown, pink or clear.

-Rod