I have a 98 Ford Explorer, on a few occasions i have parked my car in my driveway which is level the next morning i come out and the car has moved about 4 foot. Its an automatic anybody know what would cos this to happen with nobody in the car and it’s in park???
It sounds like you don’t apply your parking brake even though you’re supposed to. In that case, you’re relying on the parking pawl to hold the car. Yours might be broken or worn. Does the car stay in place if you put it in park on a hill without the parking brake on?
Does the gas level go down too? Got a teenage son?
My guess would be the parking pawl is not locking the tranny shaft.
An automatic transmission couples the output of the motor’s crankshaft to the input of the transmission through a device called a “torque converter”. This device is like a bagel sliced and hollowed out with vanes and fluid inside. As the front half spins by the engine, it drags the fluid which drags the back half (the tranny half) along. That’s what gets your car started rolling and it’s what allows you to sit at a stoplight with the engine running but the wheels stopped. The energy from the engine is absorbed by the fluid and dissipated as heat rather than pulling the car forward.
However, because this fluid is the only connection between the engine and the tranny when the car is stopped, it leaves the tranny and thus the wheels free to turn when the engine is off, the fluid being the only connection. To counter this problem, designers put in a “parking pawl”, which is a device that mechanically locks the tranny shaft in place when you put the car in “Park”. If that’s not locking in place, or is otherwise broken, your car is pretty much free to roll.
A good quick test is to have someone in eth car to push the brake (for safety) and try pushing it manually with the engine off and the tranny in Park. If you can get it rolling, your parking pawl is definitely broken.
Do you have a teenage son/daughter who may be “borrowing” the car at night?
Nothing to add other then…it is an older vehical and all what @same and @lion are saying are all possible. It might be more difficult to explain if it were an new car. In the mean time, I would assume what has been said is true and you do have a slight grade that you may not notice. I would chock the wheels if there is any chance that the vehicle could cause any damage. If it can roll in your drive, it isn’t to be trusted anywhere else either so I would take necessary precausions wherever you park it. It is winter amd you may like many , be reluctant to the parking brake overnight. If you don’t that’s another reason to chock the wheels.
If everyone is wrong, you may have some pretty rugged night creatures wondering about.
Get in the habit of zeroing the trip odometer every time you park your car at home. If your car has moved, check the trip odometer. To catch an even cleverer unauthorized user Zero your odometer at work and note the miles when you get home.