We’re all familiar with the automakers’ longstanding best-in-class horsepower and towing-capacity wars. Each model year seems to feature a vehicle whose brute strength and towing capacity dwarf those of the outgoing models.
Lately, automakers have found new turf over which to battle: the number of automatic transmission gears.
No self-respecting automaker, it seems, will introduce a new vehicle these days with fewer than six gears. Move up the price hierarchy, and eight- and nine-speeds are common. And now, 10-speed units are entering production.
This all means better performance and fuel economy for us motorists. But it also means we need to be more diligent about maintenance since today’s designs feature more gears, clutch packs and narrow oil passageways that require a steady supply of high-quality fluid.
Whether you’re driving the latest car to grace the cover of the car magazines, or your vehicle was built the same year you bought your Y2K rations, the consequences of low fluid are generally easy to notice:
• Inconsistent, jerky shifts
• Increased transmission temperatures
Low fluid = poor shifting
Transmission fluid serves a number of vital functions, one of which is to act as a hydraulic fluid to enable shifting. When your vehicle’s computer tells the transmission to change gears, hydraulic pressure (provided by the fluid) squeezes a series of plates together inside a clutch pack to connect the engine to the transmission output shaft and route power to the wheels.
Low fluid can result in the transmission fluid pump drawing air into its inlet. When air and fluid mix, they create foam, which reduces hydraulic pressure and interferes with the crisp, consistent shifts you desire when driving.
Low fluid can also prevent the torque converter from filling completely, which reduces torque transfer and causes hesitation and lost power. In extreme cases, the vehicle won’t even move unless you rev up the engine.
Wear protection key to transmission life
Transmission fluid also lubricates the gears, clutch plates and seals. It forms a protective layer between meshing gear teeth that prevents metal-to-metal contact and helps reduce wear. It helps prevent wear on the clutch plates, which bear significant friction during gear shifts. The fluid also lubricates seals and keeps them pliable so they don’t dry out and leak.
Low fluid can prevent formation of a strong, consistent lubricating film on components, inviting wear. Foam bubbles can collapse when they pass between gear teeth, allowing metal-to-metal contact and further accelerating wear.
Heat can kill a transmission
Absorbing and carrying away harmful heat from transmission components is yet another function of the fluid. Extreme heat can kill a transmission, and the fluid is responsible for dumping the excess heat into the atmosphere via the oil cooler and dissipation through the transmission housing. Managing heat, however, becomes much more challenging if the fluid level is low. Increased heat can cause the fluid to break down and form sludge, which can clog the fluid passages and lead to poor shifting.
To keep your vehicle running – and shifting – at peak performance, check the fluid about once a month to ensure the correct level. Check out this post on how to check your transmission fluid. If the fluid is consistently low, visit a mechanic to find out why and have the problem fixed.