by Alan » Tue Oct 21, 2014 11:00 pm
I've pulled my DSII with a Jeep Cherokee (torquey inline 6-cylinder) and a Toyota Sequoia (big snorty V8). Neither one seemed to notice the boat was back there.
The feature that gears automatics down when they just start to move is the torque converter. To simplify, it's made up of two turbines facing each other in a housing filled with thin oil; the engine spins the forward turbine, the forward turbine spins the fluid, and the spinning fluid spins the aft turbine, which is connected to the gears in the transmission.
All that friction (yep, there's friction, even with liquid involved) creates heat. The good news is that transmission fluid in an automatic is circulated by a pump, so you can add an aftermarket transmission cooler and the pump will push the fluid through it. Automatics from the factory generally cool their fluid by pumping it through a small tank inside the radiator, where they make indirect contact with the engine coolant. That's usually enough for normal use; if it isn't, an aftermarket cooler is an easy add-on.
Manual transmissions are generally lubricated by splash (the gears pick up oil inside the transmission as they spin, and then throw it around), and don't have a pump. A transmission cooler isn't going to do anything unless you devise a way to pump the oil out of the transmission, through the cooler, and back into the transmission.
The clutch in a manual transmission gears down when the vehicle first starts to move in essentially the same smoothly gradual way as an automatic, but it involves varying the friction between dry surfaces: the flywheel on the engine, and the fibrous friction material on the clutch plate. The variance is controlled directly by the driver, who allows partial or complete contact between the plate and flywheel by releasing the clutch pedal partway, or all the way. Friction between dry surfaces, naturally, creates a lot of heat. There's no good way to dissipate this heat unless the vehicle is moving forward, so releasing partway for a long time will burn the clutch out quickly.
Hmmm, I've gone on for a while here. One last thought: When you're looking at tow ratings, it's worth considering whether the vehicle is rated under the new or old system. There's a new system as of 2013, which most manufacturers applied as of 2011. It's a lot more realistic than the old one, and gives ratings about 20% lower for a given vehicle.
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