Torque Converter and Transmission Cooling Basics - 1967 Chevelle
Heat is a necessary byproduct of power production. The more power, the more heat. Introduce slippage in the transfer of that power and you’ll generate even more heat. Modern automatic transmissions utilize a hydraulic coupler to mate the engine to the input. The mysterious, magical torque converter. When looked at through the lens of pathways to direct connection, the converter is the stop-gap.
The torque converter makes no direct mechanical connection to the power produced by the engine. The only full-time, physical connection are the tangs on the transmission pump that are driven by the collar of the converter. In lock-up converter equipped transmissions, there is a small clutch that engages at highway speed, in top gear that locks the engine crankshaft and the input shaft of the transmission. This helps improve fuel economy and reduces heat.
So, how does a converter work and why do you care? I’m not sure you do care, but I’m going to tell you anyway. Think of a torque converter like two fans with a third, semi-fixed fan between the two. Fan #1 (Pump) is fixed to the crankshaft and spins at engine rpm. Fan #2 (Turbine) is fixed to the input shaft of the transmission and spins at the speed of the transmission. The pump spins and directs fluid outward, against the convertor body and is directed into the face of the turbine vanes. The turbine redirects this flow of fluid toward the center of the convertor and feeds it in the opposite direction, back into the pump vanes. The motion of the fluid cycles around and around. This is a basic fluid coupler.
The real magic happens when you introduce fan #3, or the stator. The stator will only spin in one direction. The big, splined outer shaft on the front of the transmission that is fixed and doesn’t spin is the stator shaft. It engages the stator inside the converter. The pitch of the stator vanes puts the “torque” in your converter.
As ground speed increases and acceleration tapers, the fluid coming out of the turbine begins to push against the other side of the stator vanes, dragging it along for the ride on its one-way bearing.
All that cycling fluid and pressure build heat. Your converter stall speed will also affect how much heat is produced. Stall speed is the rpm at which the converter will kill the engine with the transmission locked. The more aggressive your stall speed the more rpm is required before the fluid provides adequate force against the turbine to initiate movement of the input shaft. Mine is a 3,600 rpm stall.
Which is why I wanted to ensure my transmission the greatest chance of having a long life. Heat is the enemy of any lubricant, automatic transmission fluid included.
My radiator has a built-in, stacked plate type transmission cooler. As things worked out, I didn’t have much room elsewhere to install an additional, auxiliary transmission cooler.
Fortunately, Derale makes a line of transmission pans that can help ease the stress your trans fluid is experiencing. Their cooling pans feature a deeper design with integrated cooling tubes. The tubes run from front to back where they catch under-car air to help pull heat out of your ATF right where it lives. The increased pan depth allows the use of an extra quart and a half of fluid as well. Aiding in its ability to cool and dissipate heat more effectively. The best part is that it allows the use of a factory filter. The cooling tubes take up additional space below the filter pickup. So, no special adapters or filter is needed.
I won’t bore you with the gory details of swapping a transmission pan. I’ve already bored you enough with torque converter basics. But now you know why.
