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Radiator problems

I have a 2002 dodge ram 1500 4.7 liter. Its starting to overheat and the coolant is bubbling over. We changed the thermostat and drove it 6 miles and then it started to overheat again. The radiator cap is not hot and neither is the radiator itself but the coolant is boiling and bubbling so much it shoots out the reservoir hose on the side. We flushed the radiator and the engine when we changed the thermostat and started with fresh coolant.

Sounds like compression gas is being forced into coolant system.

What causes that to happen?

we bled the air from the coolant lines.

Gas being forced into the coolant system is usually a blown head gasket. Quickest way to check for this is to go to a shop where they have an exhaust gas analyzer and have them hold the sniffer over the coolant cap. If there is CO detected coming out of the coolant tank, you have a blown head gasket or a cracked head or possibly a cracked block.

However - you say that the radiator is not hot after six miles? This sounds like water is not circulating. It should be fully hot by that time. Are you certain that you installed the correct thermostat and it is not in backwards? Is the bottom radiator hose collapsing while the vehicle is running?

Getting all the air out of some cooling systems is a bit of a pain. I am not familiar with yours. Were you following a manual on that procedure?

A mechanic put in the thermostat and bled the lines for us. We told him about it still overheating and he said we could have bought a bad thermostat so he ordered us another one. Is there a chance that a new part could be bad like that? We checked the radiator hoses but not the bottom one. If water isn’t circulating would it still run out when you flush it? When it’s driving there’s no power loss or smoke that’s why they don’t think its a blown head gasket. We changed the fan clutch also and I guess the next thing to do is change the water pump. After that I don’t know what else to do with it.