Tire pressure changes for no reason

[rcs]

I’m gonna say for all 4 to be the same, the ambient temp dropped 10F and 1 psi.

My friend Rey checks his tire pressure only upon replacement. We had an argument about it. Imagine how much more carefree he is, than we at Bitog

A friend of mine never checks their's ! Their theory is the car info system will tell them when it is low. I am not that confident to rely on that! By that time it is waaayyyy too low!

 

[rcs]

The beads are where the tire meets the rim, the seal area there can become corroded and leak.

Thanks! I am going to ask the tech about that, if he noticed! Big possibility since the fill valves where corroded. Michigan weather and
salt on the roads for the last 9 years, and same tire tire rims.

 

[rcs]

A note on checking for leaks: With the tire off the vehicle and flat on the ground, you dribble soapy water where the tire meets the wheel -the bead seal. The amount of water isn't important as excess water will simply run off. The soapy water remaining will reveal bubbles. Wear your good glasses as the bubbles can be very small.

As said above: Alloy wheels corroding (oxidizing) at the bead seats is a known thing. The resulting roughness, while minor, can allow air to escape.
However, that you're seeing matching pressure differences on all 4 wheels would tell me you don't have that problem.

As others have said, temperature variations cause inconsistent pressure readings.
How 'precisely' you press on the gauge effects readings. Not only are you releasing air (not the largest source of error), but the full psi might not be hitting your gauge's guts if you hear the characteristic hissing. It's best to be familiar with one's gauge such that you can jab it on the valve quickly and squarely....not necessarily forcefully.

My wife and her sisters are taking a 1,000 mile trip come Thursday. All 4 of her tires (brand name withheld because it's immaterial) had 34 psi. It had easily been 2 months since I checked them last. She doesn't drive much, and the tires have always held air well.
I cranked them up to 38 psi (recommended 34...+ the time honored 10% for sustained highway driving = 37.4 thus 38 psi) two days ago.
I just checked them -as this thread inspired me- and they match at 38....good to go.

Aside from this particular exercise, keep in mind that the minimal/acceptable/unavoidable tire leakage is increased during the "Autumn + Spring" months. It's the temperature fluctuations through these days which increase leakage.

NOTE: I knew her rear tires were more worn...but now I see they're more worn that I remember. Time to tire shop!

That is why also I check them more in the winter months as well. Thanks for the detail.

 

[Astro14]

A 10 degree Fahrenheit change = a 1 PSI change. Driving them changes the pressure by about 4 PSI at normal speed, and up to 8 PSI at high speed.

Make certain that you’re checking at the same temperatures.

 

[eljefino]

I am still going to call the dealership and ask them to check the fill valves again and the bead around the tires. Thanks again!

Nah don't do this, they'll put their youngest dumbest mechanic on the job and "find nothing." Then what will you do with this info? You'll think there's a problem that nobody can solve, and go down a mental rabbit hole with that.

Go to dollar tree, get a spray bottle and their cheap dish soap. Mix that soap 1:10 with water and spray where the tire meets the rim as well as the valve and where the valve passes through the rim. Don't forget the backside. If there's a fixable leak, there will be a little mound of dried soap bubbles after about 15 minutes.

The dealer "Fix" for leaks is to smear "bead sealer" glue on the bead-to-rim interface. This stuff is corrosive to aluminum and also bad for tires. It's a "beater maneuver" for cars in way worse shape than yours. The best fix, if you actually do have corroded rims, is to sand down to clean metal then reinstall the tires with normal lube, and not bead sealer. This takes time and you need a "good" tire tech to work with you on this... not someone paid flat-rate who'll slap goo on and ship it out.

Your owners manual will indicate that slow leaks are acceptable. Your leak rate sounds slow. This is why we check and top off.

 

[himemsys]

A friend of mine never checks their's ! Their theory is the car info system will tell them when it is low. I am not that confident to rely on that! By that time it is waaayyyy too low!

Here's my approach:
Typically on Sunday mornings before the sun has a chance to hit any tires, I will get the air compressor with a digital gauge and check each tire on all three vehicles and get them to their known good pressure, to the 1/10th PSI. I will skip a week if the temperature is too cold or too hot for me to want to be out in it, or if I'm ill or otherwise not feeling like dealing with it at that time. No big deal if I miss a week here and there. I will still catch a slow leak before it gets too low and a major leak will become obvious to the driver and the naked eye within a few days.

I find that for the most part, while the absolute PSI may go up or down by temperature, each tire stays within 1/10th PSI of the other three unless there's something going on.

 

[rcs]

A 10 degree Fahrenheit change = a 1 PSI change. Driving them changes the pressure by about 4 PSI at normal speed, and up to 8 PSI at high speed.

Make certain that you’re checking at the same temperatures.

Agree, that is why I always check them in the morning before I leave for work in my garage. There is one window that a tire faces and sometimes that will register higher. I get that because the sun comes in there sometimes. But I am usually leaving for work at 6:30 or 7am.

 

[goingplacesanddoingstuff]

The new fill valves were put in on Tuesday the 13th. He put in 35 PSI which is what the tire and car suggests. Wednesday, Thursday and Friday it was pretty steady. I did not drive yesterday, Saturday. This morning is when it went down to 34, in all 4 of them. I just put it
up to 36, because I like a cushion. I will see if it holds Monday morning. Thanks for all of your advice and input, it truly is appreciated.

If all four are the same psi, the psi drop is not because of leaking. This is just the weather.

 

[rcs]

If all four are the same psi, the psi drop is not because of leaking. This is just the weather.

Makes sense...thanks for setting my head straight. I put them all up to 36 which is where I like it anyway. So I will see tomorrow morning
and factor in the temperature drop tonight!

 

[John105]

A friend of mine never checks their's ! Their theory is the car info system will tell them when it is low. I am not that confident to rely on that! By that time it is waaayyyy too low!

I told Rey, it’s 3+ psi lower in the fall and more in the winter. He said, “So?” Again, no need to check because 5 years from now when he gets new tires, the tire shop will handle it.

Impossible to reason. He has a lot of what I think are extreme opinions about many things…

 

[John105]

Makes sense...thanks for setting my head straight. I put them all up to 36 which is where I like it anyway. So I will see tomorrow morning
and factor in the temperature drop tonight!

Does your Jaco go to tenths like mine?

Pretty interesting. I’ll fill at Costco with their machine. I overfill, let cool overnight, and then adjust by letting some out, making all 4 exact to the tenth. They stay as such going forward for a long time (month or more).

Before I let anything out? All tires are within 0.3 psi. Sometimes they are exact. So Costco’s equipment is good based on what I have seen…

 

[rcs]

Does your Jaco go to tenths like mine?

Pretty interesting. I’ll fill at Costco with their machine. I overfill, let cool overnight, and then adjust by letting some out, making all 4 exact to the tenth. They stay as such going forward for a long time (month or more).

Before I let anything out? All tires are within 0.3 psi. Sometimes they are exact. So Costco’s equipment is good based on what I have seen…

Yes, exactly my digital Jaco does go to tenths. Sometimes if I am really strict about it like in the winter I will definitely make them all the same. Right now, 3 of them are at 36.5 and 1 is at 36.4. I keep track in my head. I also have a portable tire inflator that is good also. But my ultimate measurement goes by the digital Jaco. And I keep mine in the house not in my garage so that the battery in the Jaco is not skewed by the garage temperature.

 

[spasm3]

The only tires I checked every day, was when I had a motorcycle.

 

[ripcord]

One thing I didn't see mentioned is that every time you check the pressure, you're letting a bit of air out. It doesn't take much to lose a pound or two worth of pressure. Also, the valves in your wheels are probably not designed to be used constantly so checking the pressure all the time may wear them out faster, increasing air loss.

Instead of using a gauge to check the pressure all the time, you could use an app on your phone and a Bluetooth interface to do it via the car's computer and the built in tire monitoring system. I like the Torque Pro app for this. It also will tell you lots of other things about your car that you may or may not enjoy obsessing about.

 

[rcs]

One thing I didn't see mentioned is that every time you check the pressure, you're letting a bit of air out. It doesn't take much to lose a pound or two worth of pressure. Also, the valves in your wheels are probably not designed to be used constantly so checking the pressure all the time may wear them out faster, increasing air loss.

Instead of using a gauge to check the pressure all the time, you could use an app on your phone and a Bluetooth interface to do it via the car's computer and the built in tire monitoring system. I like the Torque Pro app for this. It also will tell you lots of other things about your car that you may or may not enjoy obsessing about.

Good thoughts. I absolutely try every time to get a direct connection to the valve. Although yes a small amount of air may escape, but not even close to 1 lb. I do have a tire pressure monitoring system, but it never correlated with my hands on measurement. Now I know why! Those batteries per the tech are only good for 7 years! The TPM on the car was at times off by 1 lb.
Thanks for the app info!

 

[vavavroom]

Just realize that tire pressure is going to vary with temperature. I set mine after an overnight sit, 1-2 pounds over, and check monthly.

No need to check daily, but if it makes you feel better sure. But your tire pressure is going to vary everyday.

If all four tires lose the same amount of pressure overnight, I'd certainly suspect an ambient temperature differential. A 10° F temperature drop causes a 1 psi drop in pressure. I see that a lot here. 90°F during the day, 55°F in the early morning.

 

[vavavroom]

"A man with one watch always knows the time, a man with two is never sure."

Fun trivia: International Atomic Time (TAI - based on the French language's order of words) is established by averaging the time of 450 atomic clocks from all over the world. This is the basis for UTC, albeit without leap seconds. UTC slowly drifts ahead of UT1 (Mean Solar Time) and 1 leap second is added to UTC about every 18 months.

 

[goingplacesanddoingstuff]

If all four tires lose the same amount of pressure overnight, I'd certainly suspect an ambient temperature differential. A 10° F temperature drop causes a 1 psi drop in pressure. I see that a lot here. 90°F during the day, 55°F in the early morning.

Also keep in mind the sunny side of the car can be a couple psi higher due to differential temperatures too.

 

[factorytuned2012]

My tires start off 1-2 pounds lower depending on temperature and if the vehicle is parked in the sun they’ll go back up through out the commute. Don’t know if there’s a magic number but I think for every 3-5 degrees +/- pressure will either go up or down.

Google says for every 10 degrees expect +/- 1 lbs.

 

[Kira]

Nitrogen vs Air...the new 'thick vs thin' debate.