My blazer overheats within 10 miles of driving and That's from a cold motor, I have no heat, and when I start the motor there is zero change in my coolant level when the radiator cap is off as if there is no vacuum draw on the system. I can't find any leaks other than when it boils out when it's overheated. Do you guys think it's a bad water pump or heater core. I have already put a new thermostat in. And about 6 weeks ago my water outlet tube from my thermostat cracked and I put a new tube on then. Also I've tried jacking ps up and burping system any other advice would be great

 

I would first estabish whether the heater core was blocked by removing the hoses from it and running water through it with a garden hose. If you get flow through the core this way then it should be fine. If no flow, I would bypass the core and see if the overheating issue persists. If not, then the core was likely the problem. If still running hot, then I would suspect water pump failure. But do be careful not to get the engine too hot for too long. Hope this helps.