The bump you feel at motorway speeds could be the torque converter locking up at approx 56mph. When the overdrive is disengaged there is a warning lit up on the dashboard to warn you. If you are getting 29mph you are doing very well indeed, the best I have ever got is 27.5 mpg on a long run.
1) Leave the overdrive switch pushed in (on) to maintain my relatively good MPG, unless I need more power up hills, or I require engine braking for reducing speed down hills without using the brake. When "on" the overdrive will then automatically cut in when the speeds are right.
2) Leave the ECT switch off, unless (again) I need more power up hills, because then I can rev higher in the gears before the gearbox changes up.
3) I can't control the torque converter. That automatically cuts in, at about 56mph, to save fuel at around motorway speeds, by providing freewheeling when my foot's not on the throttle.
4) Driving normally like above, there should be no warning lights on the dash.
Have I got that about right ?
The torque converter does not freewheel, it just unlocks the torque converter so it will act like any other torque converter which does not have a lock up function, at 70mph when you let your foot off the throttle the engine will not drop to tickover and will still provide engine braking to a certain degree. It is illegal to freewheel in the UK as this will affect things like power steering and brake servo vacuum, create brake fade and also you do not have the same control over the vehicle as well. Back in the 40s and 50s there were cars that did have a one direction clutch in the drive that provided a true freewheel but they were soon phased out for safety reasons.
I understand about the ECT switch.
I understand about the overdrive switch.
But not the torque converter ! I really would like to understand it !
I find it worth flicking the overdrive off when on a long gradient on the motorway, before the revs drop too much, then flick it back on once the rise has been crested. The ECT becomes useful when I'm towing a trailer (2 motorcycles) in hilly areas with twisty roads and wanting to "make progress".
I assume it's also a good idea to flick the overdrive off and unlock the torque convertor if faced with a long, steep, downhill stretch (particularly if signed with an "engage low gear now" warning).
"Do not adjust your mind there is a fault in the reality"
A torque converter is very similar to a fluid flywheel, ie an impeller driven by the engine and a turbine connected to the gearbox, a torque converter also has a stator positioned between the two which redirects the fluid with more force onto the turbine when needed ie when pulling away, as the car speeds up and the impeller and turbine are turning close to the same speed the stator also spins as it is attached to the center shaft via a one way clutch thus no longer multiplying the torque and acting as a fluid flywheel. The lockup that you are talking about is a device which locks the whole torque converter thus giving 100% efficiency, ie input and output shafts are turning at the same speed, before the torque converter locks up it will be operating at around 95 to 98% efficiency, not all cars have this facility.
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