Isnt this usually caused by overheating?

My Bro-in-law has a 2000 Ranger with 45k miles on it. He is being told there are 2 cracks in the head. Seems unusually for a truck with such low mileage. Would going off-road and mudding and then not cleaning the motor, leaving the mud caked on, lead to this problem? Driving it hard? I'm just looking for some reasons.

Thanks

 

Caked with mud not so much...My quad (air cooled) gets caked with mud and doesn't crack. The Ranger is water cooled, so that shouldn't be too much of a problem. Driving hard can lead to abnormal failure of anything, and could have contributed. Most likely it was a weakness in the cast of the metal, and failed over time.

 

well the way he drives I'd have written it off to abuse but I guess it could be just poor casting