Q: Mechanics replaced water pump but did not replace the thermostat. Engine overheated and blew the head gasket? 2010 Jeep Compass

Hello - this is a judgement call. It is common practice, but not a "standard", to replace the thermostat when replacing the water pump. This is mainly due to access to both easily when replacing either one, and the relatively low cost of a thermostat. Thermostats do not have "wearing" items like the bearings in a water pump, and can outlast a water pump. They can, and do, however, fail unpredictably (close down tight) - sometimes. I have experienced this personally. I encourage my friends, relatives, students, and customers to replace both when repairing either - save the labor cost of a 2nd repair, and the somewhat unusual cost you have sadly experienced.

Hi there. It is very difficult to state for a fact that the malfunctioning thermostat caused the head gasket damage. If the water pump was not working prior to being replaced, it is possible that this; along with a malfunctioning thermostat (before the repairs) caused overheating damage. However, if the water pump was working, but was leaking coolant before the repairs, it is possible that the thermostat not working may have caused the damage. A professional mechanic knows the value of replacing a thermostat anytime you replace major cooling system components; like the water pump. It is also possible that the coolant system was not correctly primed; and air bubbles trapped in the system caused the overheating as well. Unfortunately, as you can see, there are simply too many variables in this instance for us to give you a definitive answer.