Why does my car have green topped valve covers?
 

Someone at toyota said it was because they put nitrogen in the tires? Wife's car has them too. I think they are ugly. I'm gona get some nice chrome ones

It's to designate that there is nitrogen in the tires. So you or whoever is filling up the tires doesn't mix it with air.

Valve stem cap.

Valve covers = what's over the cylinder head in the engine bay.

-alex

And if they do mix air with it don't panic. It just means you have air mixed with the nitrogen and that has zero effect since air is 78% nitrogen anyway. Nitrogen filled tires are a huge rip off.
Now if they would fill them with helium and make the car lighter.
For god sake do not fill them with hydrogen though.

[OT] Tcoat, I'd like to thank you for your post but being a forum newbie I have no idea how to do it. Is there a button or link I am not noticing. Or is it because newbies are not allowed to thank? Help! ;-) [/OT]

About the only good thing that filling it with nitrogen does, is that it is usually with zero moisture.

This ensures the least amount of tire pressure change as temperatures change.

-alex

I'm not even sure you can see our valve covers in our engine bays :lol:

@mav1178 has it right, nitrogen makes a difference when the tires are at temperature swings, nitrogen doesn't readily get effected by temperatures. In fact nissan made a big deal when the GT-R came out about how they filled the tires with pure nitrogen because normal air was too "unstable". It would probably only ever make a difference in that situation because they are constantly recording data on the nurburgring trying to aim for consistency with variables and such.

Nitrogen is affected exactly like any other noble gas by temperature. It will expand and contract.

H20 molecular bonds in the tire can be broken by temperature changes.
Then the individual 0 and H molecules take up more space than they did before.

Won't matter in the slightest on the road. Track bench racing appellation.

Nitrogen is not a noble gas. But you're right it will expand and contract with temperature changes. Like any gas.

Nitrogen will expand and contract... however, not to the degree of plain old air. So for example during an autocross session, you start when it's cooler out and after a few runs your tires are hot and when you finish later in the day when it's even hotter your tires will go up several PSI. Nitrogen will only go up a few PSI. I'm not good enough to worry about tire pressures yet but all the better drivers are constantly fiddling with theirs

Derp. True.
Tires are still permeable though. Nitrogen leaks out at a slower rate than smaller atoms.
Helium will leak faster. Hydrogen would fall out faster than anything.
Oxygen would leak out slower than Nitrogen, but if you had a bag full of Oxygen in a crash, you may have a bad day.

There is a minimum number of posts before you can thank...IIRC, it's 10.

You do realize I was joking about the other gases? Hydrogen in you tires would be a bad bad bad idea.