The downside is, water creeps into your fluids including those who shouldnt have any in it.
Also your tires will get out-of round perhaps permanently.
Also gaskets may dry out, if given enough time that may include your engine gaskets.
As a minimum one should get the car and <all> its fluids up to full operating temp, also be sure to turn on the AC, even if only on defrost, if u dont want to create uneccessary leaks in your AC.
Fred...
