We have had temperatures in the 90’s for a while. In the last few days the information system built into my 2011 Malibu indicates that the pressure in all tires has dropped below 30. I thought pressure rose in hot weather. Any suggestions?
I’d get a good (dial or electronic) tire gauge and check them out. I agree, kinda odd.
What pressure do you normally keep your tires at? When is the last time you know they were at that pressure?
Hot weather is immaterial. If your car has been parked, even 90 degrees F is considered as a cold pressure reading. Driving the car heats 'em up. Then the tire pressure rises. It’s possible you adjusted the pressure when the tires were hot and everything seemed fine… until they cooled down to outside temperatures.
This bit of academia does not explain your low readings however. For now, just add air to all tires and continue to monitor the situation.
Air entrapped in a fixed space will increase in pressure with temperature, however you may have slow leaks (such as in the valves perhaps) that are exascerbated by high temperatures and allowing the pressure in the tires to drop.
Get a good dial gage, fill the tires to the pressure stated on the door jam, monitor them, and let us know the results.
While the onboard Tire Pressure Monitor can be useful for alerting you to sudden loss of pressure while you are driving, it is absolutely not a substitute for checking your tire pressure manually every few weeks.
The money spent on a cheap gauge will be essentially wasted, as the cheap ones tend to be inaccurate and also do not last very long. Against my advice, a friend of mine bought a Slime brand (no joke–that is the brand!) dial-type tire pressure gauge because it was cheap. When it ceased functioning within ~ 3 months, he found that he had wasted his money.
If you invest in a high-quality dial-type pressure gauge, it should outlast several cars. The one that I use was purchased circa 1986 from Brookstone, has outlasted 4 of my cars, and has proven to be a very wise investment–despite its high purchase price.
It might be coincidence, and not the hot weather. Check the tires for foreign objects.