Q A Coolant Lines Throttle Body Connection Cadillac 4 6 Northstar Links below: cadillac northstar engines are known for overheating. this deville had a slow coolant leak & a history of overheating due to a failed water pum. If the engine was at or close to operating temp when you pumped it up . yes cooling down could explain it . a better test is to pump it up to 20psi with the engine cold . then it should hold that same pressure for literally hours .
Northstar Engine Coolant Flow Diagram Install the thermostat housing to the intake manifold. tighten the thermostat housing bolts to 18 ft. lbs. (25 nm). refill the cooling system using a 50 50 mixture of water and ethylene glycol antifreeze. install the air cleaner and beauty panel, if removed. start the engine and check for coolant leaks. Posted june 22, 2011. drain the cooling system enough to remove the hose. when refilling the system, just fill it to the top of the neck and it will settle. once it stops settling, start the engine and keep it filled to 2 1 2 inches below the neck of the surge tank. the system self purges the air so there is no need to fill through the radiator. If low speed fans cannot keep the temperature under control, the fans will turn on high speed at 234 degrees f. a few degrees of fluctuation is perfectly normal so an engine temperature of 195 to 238 degrees f is perfectly normal for a northstar and is nothing to be alarmed about. cooling fans come on low speed: 223 degrees f, or 106 degrees c. Not the same as overflow line. purge line comes in on top side of serge tank towards engine, a small hose. it converts to metal line and runs to just above water pump where converts back to rubber line and it connects to the infamous "hollow bolt". that is what gets plugged not the line itself.
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