When and How to Test your Car's Thermostat

Most gasoline and diesel engines include a water-based cooling system to remove excess heat caused by combustion. A coolant circulating through the walls of the engine picks up heat and carries it into the fins of a radiator where moving air helps dissipate the heat.

Cooling systems are simple compared to engines. They include the water jacket, a network of passages though the engine block; the radiator and cap; a fan; a water pump; hoses and the thermostat. Though it's a mechanically simple device, the thermostat serves an important function, regulating the temperature of coolant and engine.

How a Thermostat Works

A typical thermostat. 

A thermostat sits across the opening where coolant enters the block. When the engine is cold, the thermostat closes off the opening to keep water isolated in the block. As the engine begins to generates heat. The thermostat remains closed until coolant inside the block reaches the operating temperature at which the engine performs its best. Then the thermostat opens to allow circulation of coolant from the remainder of the system. It opens wider as the coolant temperature increases: the more coolant that passes through the block and the radiator, the more effectively the system removes unwanted heat. When operating temperatures change, the thermostat can adjust to maintain the coolant's temperature within a narrow set range.

How Thermostats Fail

When it reaches the end of its useful life, a thermostat usually sticks in the open position, allowing coolant to circulate through the system continually. When this happens, an engine is unlikely to reach its optimum operating temperature, which both increases wear and erodes fuel economy. In cold weather the heater, which is in most cars part of the cooling system, will function poorly or not work at all. More rarely, the thermostat will get stuck in its closed position. In this case, coolant in the system won’t circulate through the engine block, causing the engine to overheat.

How to Replace a Timex Watch Battery Yourself

Dead watch? Install a new battery yourself.

You used to be able to walk into the local discount department store and buy a replacement battery for an inexpensive wristwatch like a Timex Indiglo or Timex Expedition, and the person at the counter would replace it for you; free. You don't get that service any more - now you have to go to a real jeweler (and suffer their disdain over not having a Tag Heuer) or a kiosk in the mall where they'll sell you a battery and install it for about the same price you paid for the watch in the first place.

You could, of course, replace it yourself... like I do. Timex stamps the battery size on the back of the case, and you can buy these batteries at your local grocery. They're usually CR2025 or CR2032 button-type batteries. Once you have a new battery, you're set.

What You'll Need

• Replacement battery: verify the battery size/style printed on the back of the watch case.
• Size 0 Phillips-head screwdriver (you can find one in a set of jeweler's screwdrivers for a couple of dollars)
• Sheet of plain white paper