Where is it leaking? That pressure test sounds funny, why would you pressurize only the pump and radiator? If you are leaking coolant outside the engine, locate the source. If you are losing it from the radiator but cannot find a puddle suspect a head gasket problem. Check the Radiator cap first, if it is bad high pressure coolant will travel back to the overflow bottle.
Blown head gasket? Air trapped in the system (hasn't bled out yet)? Wrong cap?
Sounds like the thermostat is stuck open. Replace the thermostat.
Drain the water from your radiator. Remove the radiator hose, from the thermostat housing. Remove the thermostat housing retaining bolts. Replace the thermostat housing gasket and reverse the process to install the new thermostat.
First, remove the radiator cap and start the engine.The engine should be warm enough for the thermostat to open. (The fluid can be seen to circulate once the thermostat opens), Be careful of the now hot fluid that it will not burn you. There is most likely a radiator plug at the bottom of the radiator but if not, remove the bottom radiator hose and allow the fluid to drain out. If you want to flush the system you could refill with plain water (close the drain plug) and allow to circulate for a few minutes then redrain. There are commercial products for flushing the system readily available. Once emptied (and flushed), close the plug or reattach the bottom hose and fill with the appropriate mix of antifreeze and water. Read on the antifreeze container for the dilution ratio for the desired low temperature protection.
I would check the hoses leading into your radiator, and also the overflow for antifreeze. If that is not the problem, it could be your heater core. Your heater core might be leaking, you might have a hose leaking
Is it leaking from the water pump or radiator? Is the system properly pressurized?
The best indication of a bad thermostat is when the radiator fluid (Antifreeze) boils over from the reserve tank, not the radiator. This is caused by the thermostat not opening at its preset temperature and all the extra antifreeze is pumped directly to the reserve tank. You will also have loss of power and the vehicle will likely stop running soon after the antifreeze boils over.
To replace the thermostat on a 91 Cavalier you need to drain the radiator. Remove the top radiator hose and water inlet. Remove the thermostat from under the inlet. Install the new thermostat and reinstall the inlet and hose. Fill the radiator with fresh antifreeze.
If the thermostat is stuck open, the radiator is able to cool the antifreeze faster than the engine can heat it.
Drain the radiator into a container. Remove the upper radiator hose at the engine and remove the 2 bolts in the thermostat housing. Remove the thermostat and clean both surfaces. Install the new thermostat and upper hose. Top off the antifreeze.
Drain the radiator into a container. Remove the upper radiator hose at the engine end. there is 2 bolts in the housing that hold the thermostat. Remove them and the thermostat and clean both surfaces. Install the new thermostat and housing. Install the upper hose and top off the radiator with a 50/50 mixture of antifreeze and water.
Sounds like you need to flush the radiator and replace the thermostat
Drain the radiator. Remove the top radiator hose on the 2003 Buick Century. Unbolt the hose inlet. Remove the inlet housing and take out the thermostat. Replace the thermostat, install the housing and top hose, and refill with antifreeze.
Thermostat messed up, Oil needs to be changed, no antifreeze in the radiator, radiator fan is not working properly
generally located where the upper radiator hose meets the block, under the throttle body Follow the upper radiator hose to the engine, there should be the thermostat housing. And there is no drain plug on an 2002 Monte Carlo 3.8 v6 , so you will lose less antifreeze if you just disconnect the upper radiator hose from the thermostat housing then hold that hose up. I only lost maybe a quart of antifreeze.
remove some of your antifreeze,disconnect top radiator hose,remove 2 bolts holding thermostat cover remove thermostat and scrap sealant off both sides and put more sealant on and install thermostat and tighten 2 bolts and add more antifreeze.
I suspect that either your thermostat is plugged with debris from the radiator change or that the thermostat was replaced backwards. The spring side should be towards the block.