Veins and Venules: Veins are the large return vessels of the body and act as the blood return counterparts of arteries. Because the arteries, arterioles, and capillaries absorb most of the force of the heartâs contractions, veins and venules are subjected to very low blood pressures.
Wondering when to change your automatic transmission fluid (ATF)? Most manufacturers recommend replacing transmission fluid every 30,000 to 60,000 miles. If you tow, or do mostly city driving with constant changes of gears, it may be wise to change your ATF even more often. Here's why. Your automatic transmission has a lot of moving parts.
Most manufactuerers say the automatic transmission fluid will last over 100,000 miles with average use. But severe service rquires fluid changes every two years or 24,000 miles. Severe service can mean extended high speed driving, trailer towing, or just driving normally in cold weather. Some manufactureres (like Subaru) state that under severe  conditions you should change the AT fluid and filter every 15,000 miles. If the fluid is bright red and smells sweet, it is pobably still usable. If the fluid color is dark red or brown and smells burnt, change it.