As 4hero says, using the manual mode is well worth it, but takes some time to learn how to use it and sometimes, like when you have friends or family complaining you take too long taking photos, the semi-auto modes can be pretty useful too!
In your photos above where the sky is all washed out, the problem is the camera has taken the light reading from the black car and set the camera from that, so the brighter sky is over exposed. There are two reasonably simple ways you can quickly compensate for this while using the semi-auto modes on your camera.
1. Exposure locking
Frame your picture as you want it, then move the camera to centre on the brighter area e.g. point at the sky. Half press the shutter and the camera will auto focus and take a light reading, at this point press the Exposure lock button (not sure if its the same on a Nikon, but on Canons its a "*" button just under your thumb), you should see the exposure lock indicator appear in the viewfinder. Now re-frame the picture you actually want and half press again, this time the camera will only auto focus and keep the locked light readings - now take the photo and the sky should appear correctly. Obviously the exposure balance will depend on where you take the light reading, if its too light, your car will be under exposed, so you need to find the right balance, although you can also use fill in flash to compensate for the darker subject!
2. Exposure Compensation
On a Nikon I'm completely lost how to do this, but there is a setting that allows you to adjust you exposure level. You may have to go into the menu to select the function to adjust the setting, its normally shown as like a scaled ruler display with a dot that shows the current setting and can usually also be seen in the viewfinder. You can change the exposure compensation either to the left (darker) or to the right (lighter) in 1/3EV (or maybe 1/2EV) steps. Using this feature, you take the photo as normal just framing the car and the compensation value you set will adjust the exposure. So in this case you would set a couple of stops to the left and the sky should be correctly exposed.
Once you learn how to use them, they are two handy features to quickly get the right exposure while keeping the camera semi-auto and avoiding annoying your friends or family