simply fact is if the tires are losing air pressure they have something leaking. Could be the stem leaking at the rim, the valve core, around the rim from debris on the rim or tire when the tires were mounted or a small pin hole it the tire. I have the same issue on our van. ONE tire seeps down and after a few weeks the low tire pressure light comes on. Spec calls for 36 psi, while manual says the indicator light will come on around 45 psi on the high side and 28 psi on the low side. So you could be a could of pounds above the minimum then cold temperature cause the pressure to drop slightly until you drive some - just as mentioned. If you go weeks without having to add air the leak would be hard to locate, and could require dismounting the tire from the rim to cure.
I just started and moved a car that has been parked over 2 years with all the tires very low, but none "flat"; the lowest showed 2.5 psi. Tags expired in March 2013. I think they did good, and have stayed up since. Ready to go to it's new home soon.
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