Your bottom hose is cold because the coolant thats in it is cold, and the t-stat hasn't opened yet. I don't know how cold it is by you. Here is northeastern Wisconsin its winter. I have my radiator blocked off and I drive 45 miles to work and my t-stat still hasn't opened. After I got the car I put in a coolant heater and replaced the t-stat. When you do this you want to let the car run to get out the air in the system and top of coolant at the right level. Anyway it took over 2 hours for the coolant to cycle meaning the t-stat opens and engine is at oper. temp. this is normally when the radiator fans kick in the (temp sensor tells them to).adamrc said:I'm having the same issue here. My water temp usually stays around 172-176. I replaced the coolant temp sensor with the updated green one not too long ago and now I noticed that the upper radiator hose is hot while the bottom one is cold. Would this be due to a bad thermostat?
I would swap out the t-stat in spring or summer, because the car wont take as long to warm up.
The t-stat's job is to stay closed till the motor gets to the temp the t-stat is rated for(eg:195*). After coolant(hot) flows through open t-stat to the radiator to the upper hose(not as hot) back in the engine taking the heat from the motor back to the radiator to cool off. No matter if the t-stat is open or closed your water pump is moving the coolant through smaller hoses. eg: To your heater core. This is why you have hot heat inside, if you never have hot heat then you got a t-stat problem (not always but most times).