Quote:
Originally Posted by JRTJH
The part I bolded is the reason why overfilling can damage the tank. As DEF freezes, it expands. Overfilling the DEF tank can cause the damage. It only occurs in locations where the temperatures are cold enough to actually freeze the DEF solid. I would make a guess that's in places where the temperature is below zero for days and days and on trucks that sit outside, unprotected from the temperatures. Our truck is in the garage "at home" but if we go to visit someone overnight or take a trip and stay overnight, we usually wind up parked outside... RAM and GM trucks "may" (I don't know) a means to create expansion room in the way their DEF tanks are molded. On Fords the tank can be "filled to the very top with no air gap or room for expansion"...
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DEF does freeze at -11C or 12F... Ford has a heater in the tank... I know this because it was just replaced under warranty which was extended because of a problem with the heater..
Down here 12F is pretty rare so I have little knowledge of the operation of the heater other than a warning light came on when it failed..
Wonder if it works with the block heater if the truck is so equipped.