I have two cracked motor mounts on my KIA Sadona. I am curious as to what may have caused this. I am wondering if driving longer distances could cause it to happen
It is a 2004 Kia Sedona EX. I bought it in April.
The main thing which damages motor mounts is the torque provided by the engine (the twisting motion the motor mounts are preventing). When you are driving down the highway on a long cruise, you are actually putting less torque the motor mounts than you would if you were in stop & go traffic. Any motion causes wear on your motor mounts, but highway driving is going to cause the least amount of wear on them when compared to other types of driving.
A few factors contribute to rubber inserts within motor mounts to fail.
The rubber decays over time and loses it's elasticity. The degraded rubber fails slowly over time.
Some chemicals can accelerate the decay of rubber. Certain acids such as hydrofluoric and hydrochloric will degrade Buna-N rubber. EPDM rubber can degrade from gasoline or glycol ethers contained in brake fluid.
Shifting from park to reverse then to drive does the most physical wear.
Add the three together and considering you have a 2004 vehicle it's completely reasonable that you've had a failure.
Highway driving is probably better than the car just sitting as the motion and input help to keep the rubber pliable for longer. Counter intuitive.
Replace it and good luck!