Hi, everyone...I was hoping someone could help me with this problem...Got my car 3000 miles ago..Tire pressure always read 34 front 33 rear ..Yesterday it read 29 all around and a idiot light lit up on the dash with a flashing psi light in the gauge...The temperature outside cooled down to 64 degrees....I stopped at a tire place and check the pressure manually...29 in all tires..After I filled them back up to 34 front 33 rear the error light went off..everything back to normal
..Am i supposed to put air in and take air out each time the weather changes.
Is there a 4lbs setpoint before you get a error...seems too close .

Or is there something wrong with the system and should i bring it back to the dealer

 

I believe the warning is fixed at 29 psi. Also, it is possible to have a drop of 4 psi based on the weather. Tire pressures should always be checked cold (after the car has been sitting). Even on a cold day, driving the car for a few miles can heat the tires enough to change the pressure. The sticker on your driver's door tells you what the pressure should be when the tire is cool to the touch.

 

The TPS is working perfectly. What you experienced, is normal. Now, if you filled your tires with nitrogen you would not have that problem. Problem is finding a place that has a nitrogen tank, unless you work around aircraft.

 

I just happened to have some nitrogen..I'm in the HVAC business..Just never heard of filling your tires with it....but thanks for your response

 

So you understand why it's used in aircraft tires, off road trucks and racers that can have it. Nitrogen gas is inert, so your pressures don't rise and fall with the temp. Plus, you are less likely leak at the bead because of the larger molicules.

 

The TPS alarm goes off at 28 psi. Give or take a PSI and you were on the limit.


I have a question for you guys that are using Nitrogen. How are you purging the air from the wheels? All stock and most aftermarket wheels have only one valve stem. The race wheels that I've seen using N have two stems, one to fill and the other to purge the air out.

 

Nitrogen is a gas and will be affected by temperature changes. PV=nRT. The fact the N2 has one less proton, neutron, and electron (ie smaller than O2) doesn't keep it from leaving the tire just like air, which is 78% N2 and 20% O2 anyways.

The reason most use high grade N2 to fill tires is that it is INERT. The O2 in the air can react with the rubber compound and degrade it (oxidize it) over time. This effect is most imporant in tires that become very hot during driving (ie racing, landing strips, hard impacts (compression). N2, being inert, will not react with the rubber, adding life to the tires. Most of us will run out of tread before this affects us. Only weekend drivers may see a benefit.

Another reason people may use N2 in tires is because the volume expansion ratio of N2 is lower than O2 (696 vs 860 respectively). This would result in a more constant tire pressure over the same temperature range compared to air. This seems like a small benefit as air is 78% N2 to start with.

Not trying to be harsh here. Just like to see physics represented correctly

 

I didn't take it as harsh. I'm always up for learning something new. Your explaination is much better.

 

Hey, learning keeps ya young. Important at my age and in what I do LOL