Overheating issues

Hi all, How would I know if I have a coolant pump/thermostat issue? I have replaced the coolant pump (which was a mare ) arond 500 miles back and all has been fine up until the other day, took car out for a spin and all of a sudden the temp gauge sky rocketed, luckily I was close to home so i could get the car back. I have undone the bleed screw near the ECU’S and turned the heating on full, cool air comes out of the vents and the coolant pulses every 5 ish seconds fron the bleed screw, the hoses around the bleed screw are also cool, I tried another coolant replacement under vacuum and the pressure held which indicates no leaks. any ideas?

There is a good chance that you have a air pocket in the coolant system. If you’re getting cold air out of the heating vents. After the car is warm. That’s usually a good sign that there is a pretty decent air pocket that is preventing the water circulation.

The first thing you need to do is to get the air out. So I would look into that. Is not likely that you got a bad coolant pump but I’d feel the discharge hose to make sure there is pressure there as well.

I can’t answer as to HOW the air pocket formed, but when I’m doing the final bleeding through the heater core bleed screw, I like to give it a few revs before closing it up; seems to force any last air out of the system.