Why do we need to check the level with the engine hot? Why is there not a cold level that can be checked?
Wouldn`t the level be more consistent with the engine and tranny cold and turned off, with the fluid just sitting in the bottom of the case?
What`s up?
Some cars do have a cold checking range marked on the dipstick, but the hot reading is the preferred one. Apparently there are variations in how much the fluid expands when hot, and fully warmed up is the standard operating condition that readings are based upon.
With the engine running, and thus the transmission’s pump running, all the various valves, clutches, etc. in the transmission are filled with fluid. Again, this is the standard operating condition. Some of the fluid will drain down when the engine is off, giving a false high reading. The exception here is Honda/Acura, which specifies checking tranny fluid level with the engine off (but warmed up, and within a minute of shutting off the engine). Their automatic transmissions have some key design differences compared to everyone else’s.
I don’t know the precise technical details, but apparently automotive engineers have determined that the changes between hot and cold and between running and not running present inconsistencies.
Thankyou much.