Low tire pressure in Nitro filled tires
 

I have an '08 TL that my wife and I bought a couple of months ago and I love it! BUT... Since it has been getting cold at night every morning the Low tire pressure warning light is on and read 4-5 psi low. The tires are supposedly filled with nitrogen according to the dealership. My understanding is that with nitrogen filled tires they should not lose pressure like this. I know its not a leak because the pressure goes back to normal after the tires warm up a little. Any ideas on why this is happening or if it is actually normal with nitrogen?

1) Put some air in your tires when they are still cold-- at least to factory recommendations if not higher. Don't trust the gauge on the air pump, either-- use your own gauge or the TPMS.

2) Air is affected by temperatures more than pure nitrogen. Unless the dealership vacuumed out all the air from the tires before putting in nitrogen, the tires will have mostly air in them, topped off with nitrogen.
Air = 78% nitrogen, by the way, so I wouldn't pay for nitrogen/Nitrofill, etc.

Welcome to AZ.

So is it ok to mix them like that? I mean I wouldn't think it would do any harm just want to make sure. Also, the tires were brand new and put on by the dealership. I just don't understand why it is fluctuating so much if they are in fact filled with nitro.

You fell for the nitrogen scam.

It makes no difference in fluctuation the way it's used in street cars. I tried it just to say I told you so and I saw the exact same fluctuation from cold to hot. Just add some air to your tires and you're good to go. Of course you can mix, as it was said, air is mostly nitrogen.

I didn't fallfor a scam... they were already "nitrogen filled" when I test drove the car so when we bought it they had nitrogen.

Regardless, you can just top them off at an air pump to get to the proper tire pressure. That whole thing IS a waste of money, so as long as you don't fall for it again or paid for it the first time, you're good.