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Re: air in cooling system
You need to remove the upper most heater hose from the heater core and raise the hose up high . Fill the rad until coolant comes out of the heater core pipe. Carefully reattach the heater hose. Fill the rad slowly allowing trapped air to escape.This may take a while. Once the rad is full put a catch basin on the floor under the rad filler neck.Start the car and let it run to operating temperature.Allow the expanding coolant fall into the basin.Once you see circulation in the rad you can slowly top the rad off.Once you do this replace the rad cap and fill the reservoir bottle 3/4 ways to the top. Shut the car off and let it cool off filling the bottle as necessary.It's a lot to do,but it works for me every time :-)
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When you changed these components and refilled the cooling system, did you purge the air out of the top of the system by opening the bleeder valve. These engines have coolant in areas higher up in the engine where air can be trapped during refill. Air trapped in the system will cause overheating issues. Otherwise, the only thing you haven't mentioned in the system is the radiator and fan assemblies. They could be suspect, as could a possible blown head gasket.
Many cooling systems are well designed and are self-purging. A few need to be carefully refilled and sometimes a hose or two needs disconnecting. Sometimes there are strategically placed cooling system bleed screws.
These days there are clever tools available to help avoid the fiddling about needed to bleed air from troublesome cooling systems. Basically it is a vacuum pump that evacuates the air from a cooling system before allowing atmospheric pressure to charge the system with coolant from a reservoir.
Start by repeatedly squeezing all of the coolant hoses you can access. While doing this you should see bubbles coming up through the radiator cap opening. After doing this for awhile, top up the coolant and drive for a bit. After the car cools down you may want to repeat the process. Keep checking it for awhile as properly "burping" a coolant system can be a pain and take awhile. You know you're done when there is no more air at the top of the rad cap after driving (and letting it cool down)
Well Michael put your hand on radiator upper hose and then the lower hose right after car warms up and just starts overheating is there a temperature difference if so one of two things is going on thermostat not opening even though it is new or there is still an air bubble in the cooling system if nthere is no difference and still overheating might have to explore headgasket being blown
air in a fluid system always goes to the highest point in the system. ensure that the heater control is in the fully on position. Find the highest point in the cooling system and loose off/remove the hose at that point to allow air and water to flow out Refit and refill the radiator . As a point of interest ,,water pumps are seldom the cause of overheating. They leak and make a noise but the overheating will not occur until the coolant level is reduced . I would be looking at a partially blocked radiator , head gasket, cracked head , condition of radiator core fins and faulty thermostat.
Check for coolant flow at the Purge line,this is a common problem on the Northstar. There is a small diameter hose coming from near the top of the coolant tank,this is the purge line. With
the engine idling,pull the purge line from the tank,if there is no
coolant flow from this small hose,it is blocked and this will cause
overheating.If the hose is clear, check for blockage at the nipple on the tank.
Air locks in the Northstar engine shouldn't be a problem as the system is self purging.
Are you using a TOYOTA thermostat? The OEM 'stats have what we refer to as a "wiggle valve", and the 'stat should be inserted with this valve point straight up to 12 o'clock. This allows air to be purged from the cooling system. If everything is good, you may just have a "air blockage"; the system will not pump air in the cooling jacket, the water pump will just cavitate the air, resulting in your overheat condition...