The heat never lets go
Everybody knows Phoenix is hot. What matters mechanically is that it does not stop being hot at night.
Through much of the summer the overnight low stays above ninety, and the asphalt and concrete of a large city radiate stored heat back for hours after sunset. A car parked outside never returns to a resting temperature. The heat soak is continuous for months rather than daily.
That is the difference between Phoenix and a hot climate that cools at night, and it is why things fail here that survive elsewhere at similar peak temperatures.
Batteries have the shortest service life of anywhere in the country. The chemistry that destroys a lead-acid battery accelerates with temperature — grid corrosion, water loss through the vents, plate degradation — and here that clock never slows down. Three years is a normal life and four is fortunate.
Plastic is the specific cooling failure. Radiator end tanks, thermostat housings, coolant elbows and expansion tanks are moulded plastic, and continuous heat cycling makes them brittle. They do not weep first. They split, at once, usually while hot and usually a long way from home.
An arterial grid, not a freeway city
Phoenix is laid out on a mile grid of wide surface arterials, and a great deal of driving here is on them rather than on freeways.
That is stop-start driving at signals, at full vehicle weight, with the brakes doing all the speed control because there is not enough speed for aerodynamic drag to help. Pads are consumed at a mileage a highway car would not approach, and brake dust plus heat is what seizes a caliper slide.
It is also the cooling system's worst case: crawling between lights in July with the air conditioning at full load and almost no airflow through the radiator. A fan that engages a few degrees late is invisible in a temperate climate and puts the gauge up here.
Monsoon dust
Summer monsoon season brings haboobs — dust walls that move enormous quantities of very fine particulate across the valley in minutes.
Engine air filters load at rates no service interval anticipates. Cabin filters load faster still, and a loaded cabin filter reduces airflow across the evaporator, which reduces air conditioning performance and then gets diagnosed as a refrigerant problem.
Check both by looking rather than by counting months. It is the cheapest maintenance decision available here and the one with the most obvious result.
Nothing rusts, and everything rubber dies
There is no road salt and very little moisture. Underbody corrosion is close to absent, and a twenty-year-old Phoenix car comes apart on the bench — which is a large part of why they are sought after elsewhere.
What ages the car is ultraviolet and heat working on materials. Rubber bushings and boots harden and crack rather than wearing away. Wiper blades are measured in months. Headlight lenses haze until the beam pattern is genuinely worse.
The trap is that the car looks structurally perfect throughout while every rubber and plastic component reaches the end of its life at the same time.
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