Rotary Nut

I too have been getting the intermittent TP warning light when it gets cold outside. I checked my TP, first time since taking delivery, and the pressures were way off for two opposing tires:

L/F: 26.5
R/F: 32.0
L/R: 32.0
R/R: 27.0

I set all tires to exactly 32 psi. Even though we had a supposed 40 degree temp drop last night I got no TP warning light on the dash after pulling the car out of the garage.

In the winter my garage stays at about 55 degrees because the heater to the house is in there (oil heat). So I filled the tires in the closed garage then drove it outside where it was about 42 degrees and the indicator lamp did not come on!

matt

I got the light one cold morning. I took it in just a case and the dealer added air to all the tires. He said that they were in the mid twentys.

Gord96BRG

Geez, Matt - when your low fuel light in the gas gauge comes on, do you take the car to the dealer to check if everything is all right? :p :D (Just teasing! Yours is nowhere near the first post from someone doing this, or posting here about problems with their TPMS warning light.)

It's a tire pressure warning system - if the light comes on, there's probably a problem with inappropriate tire pressures that should be checked first!


Regards,
Gordon

matt

LOL!!!

I took it in because of this...

I drove to work and the outside temp was 45 degrees. I got there @ 6:00 No light.

I left @ 8:00 and the light was on. outside temp was 52 degrees. I thought it could be the cold but I also thought I had a tire going down.

oosik

sounds like the TPMS is doing what it should........

8_wannabe

I thought the warning would come on if one tire was way out of whack with the others. Like if all four were equally low you would get no warning. Perhaps this is another vehicle type that does this, not the '8. I got a warning for the first time last night. About 58 degrees out; I had been driving about 1.5 miles at 40 mph and got the warning. I stopped immediately at a gas station to top off the air; all tires were around 28 psi.

nt5k

I've never had mine turn on yet.. Mainly because i check and top off the air before i leave the house on Saturday mornings.. I wish the system would tell you actual psi for each tire.. Not just a 'warning' when one of the wheels is off..

red_rx8_red_int

I wish it would tell you which tire to check.

rx8ntexas

I wish you could inflate and deflate the tires from the cockpit while driving...like the hummer 1 :D

eccles

Why? If it did that, some idiots would only check the one tire that it was reporting, and then get pissed if it reported another a few minutes later.

A single warning light, which forces you to check all four wheels, is a good thing IMO.

jtdwab

I agree with nt5k I wish they had sent the info to the system display. The tech highlights CD shows that the pressure for each tire is on the CAN network. Being able to look at the pressures and make a judgement would be better.

I know their are morons in the world that would see a couple of PSI in the tire and figure it was okay but I would like to know stop right now or drive conservtivly to the next gas station.

I am looking forward to the scan tool being developed by others in the forum. That will make things a lot nicer.

kittychester

my tire pressure light came on- I was having my car serviced anyway so had the dealer check my tires and found that all four tires were different and none were correct.

mikeb

just had my tires rotated at dealer for 7500 mile

got home and my tire psi was 45
BS

rx8cited

Hi all,
For snow tires, the Owner's Manual page 4-9 says:

"Inflate snow tires 30 kPa (0.3 kgf/cm 2 ,
4.3 psi) more than recommended on the
tire pressure label (driver’s door), but
never more than the maximum cold-tire
pressure shown on the tires."

which means 32 + 4.3 ~ 36 psi. This also agrees with what TireRack suggested I use for my Dunlop M3s.

rx8cited

Spinny 3ngls

from what i have heard filling the tires with nitrogen instead of compressed air will solve the temp problem as the nitrogen doesnt expand and contract quite so easily due to temp changes.

rx8cited

Great! As soon as my local Shell gas station has nitrogen available for the same price as air (free), I'll be sure to start doing that :D .

In the mean time, checking my air pressure once every two weeks works just fine - just be sure to carry your own tire pressure guage.

rx8cited

Alessandro

Spinny, all bigger airplanes got nitrogen in their tires so it´s not a bad idea. Also safer than air, air contains oxygen and oxygen is
needed when something start to burn.

f1michel

after reading all your posts guys i'm very happy that my RX isn't equiped with that gadget here in Canada. A good gauge works fine for me and i check it every 2-3 weeks.

Ron

As I recall the pressure variation with temperature is the ratio of the absolute temperatures. That is if the tires were filled to 32 psi gauge(32+14.7 psi to get absolute pressure) at 60 degrees F and the temperature dropped to 30 degrees F, then the pressure would be
[(32+14.7) * (460+30)/(460+60)]-14.7=29.3 psi. Note the 460 is to convert Temperature in Deg F to deg Rankin(the absolute F scale ) and the 14.7 is to convert from gague to absolute pressure. The type of gas doesn't enter in. It is true that the molecular weight of nitrogen is less that that of air so there would be slightly fewer pounds of nitrogen to create the same pressure.

Rotary Nut

Well ever since I started this thread I have not had my TPS light come on, not even once. The temp has dropped around 30 degrees since then. Although my car is garaged, when I back it out, the light still does not come on even when the temp drops down to outside ambient temp from the temp of the enclosed garage (usually 10-15 degrees warmer than outside temp).

I think maintaining the SAME psi at each wheel is more important then the actual pressure the tire(s) is set to. Whether the psi is 32.5 or 29.8333, as long all tires ARE THE SAME then you should be okay.

I think the pressure difference between tires was being misconstrued by the computer as a drop in pressure and thus triggering the light.

FirstSpin

Regarding the behavior of nitrogen vs. air, since air is 78 percent nitrogen, I'd be darn surprised if you'd ever be able to tell the difference. It's been darn near 30 years since physical chemistry but the difference between nitrogen or air and the ideal gas laws (at the temps and pressures we're talking about here) is minute. The differences between nitrogen vs. air relative to ideal gas law behavior would be even less. As far as the oxygen in air being a fire hazard, the tire is constantly surrounded by what amounts to an endless supply of air, the few cubic feet of oxygen that you'd remove by filling the inside of the tire with oxygen-free nitrogen would not add to or take away from the ability of the tire to burn. Air itself is not flammable under normal conditions, it simply supplies the oxidizing source to participate in the reaction that we call burning. You could fill a tire with air and spend the rest of your life trying to ignite that air and you'd end up a deranged and frustrated individual. It's pretty much not an issue....

Rotary Nut

Nitrogen is used in lieu of regular compressed air (or oxygen) because it prevents the formation of moisture inside the shock/strut/tire (whatever) due to temperature/pressure changes. No moisture means no chance of corrosion forming on the inside of the structure it is contained in. Corrosion leads to metal fatigue and metal fatigue leads to.....so on and so forth so you get the picture!

When I was stationed in Ft. Wainwright, AK we purged the Telescopic Sight Units (TSUs) on the AH-1S Cobra attack helicopters with nitrogen for this same reason. It prevented the optics from fogging and building up moisture and possibly jamming up the works with ice.

Rotary Nut

Update.
.
The temps have dropped to the low thirties and I still have not seen a single warning light since I started this thread!

Racer X-8

The sensors trigger the alarm either with just one or all 4 tire pressures being out of spec.

The indirect systems have no choice in the matter. They use the rpm's of each wheel as an input & trigger the alarm when there's a large differential in one of the 4 rpm's. If all 4 tires had 10 psi air pressure, this type of system would think that everything is peachy.

Not so with our direct sensing system. And that is good news.

rx8cited

I have two sets of sensors - one on the summer wheels and one on the winter wheels. No TPMS warnings since I've owned the car :D.

rx8cited