Just installed a new radiator from Summit. Original was leaking. Filled her up with coolant, started fine, temp gauge starts climbing, doesn't stop climbing. I had the rad cap off too see if I would need to add coolant when the thermostat opened, but that never seemed to happen. The the large upper hose never got warm. There is coolant circulating through the small upper hose. The fan never came on either by the way. I rechecked all of the connections, but I don't see anything disconnected or missing. Any ideas?

PS. This radiator is larger than the OEM. Don't know if that matters.

 

With the new radiator in and filled up, run the car. Turn the Heater on high and leave the radiator cap off.

As the car heats up the thermostat will open and you'll see the water moving around. You may see the temp gauge "spike". This is the thermostat hitting the air pocket. So I wouldn't worry too much about the what the "temp" gauge" says at this point. Unless the car is boiling out it's coolant, it's not overheating.

But I digress...watch for bubbles with the radiator cap off. As the car heats up eventually the coolant will bubble up as the air comes to the top of the radiator. When this happens it's called "burping" the radiator. After it "burps" the coolant level will drop. It should "burp" 2-3 times before leveling out. You may add coolant after each level drop if you wish. Eventually it will level off. Turn the car off at this point, put the radiator cap back on and fill the overflow to the recommended level.