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Join Date: Sep 2010
Location: Northern Virgina
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Well, Your sure that there is no air in the system and that the radiator is full of coolant ( not just the overflow tank, the radiator itself ). And you have replaced the thermostat and rad cap (aftermarket), But did you check the sealing surface on the radiator side of the cap ?? There are 2 seals here, one outer ( the cap itself) and the Inner ( this is for the pressure relief valve on the cap). If the inner sealing surface is deformed from the defective old cap then the coolant will not get pressurized ( decreasing the boiling point) and will just push coolant out into the overflow tank.
The way it should work is like this, radiator when full and cold should have the overflow tank coolant lvl to the cold line, when the engine is warming up the system will start to pressurize, once it reaches above about 13 psi the cap will open and let the excess pressure out and flow some coolant into the overflow tank and bring the lvl up to around the hot mark and stabilize.
Then once the engine is shut off and the system starts to cool off decreasing the pressure until it starts to go into a vacuum, At this point it starts pulling coolant back in from the overflow tank past the cap and into the radiator thus bringing the lvl in the overflow back to the cold mark.
Now if the radiator cap is bad (not holding pressure) or the Inner radiator sealing surface is bad the system will never gain pressure and just push coolant into the overflow tank (no pressure = lower boiling point causing more coolant to be pushed out). Now when shut off and cooling down the radiator cannot pull coolant back in from the overflow tank (no pressure to begin with ends with no vacuum to pull it back in) = low coolant on your next restart and it keeps getting worse.
And don't install a lower temp thermostat, you will just create driveability problems and possibly inhibit system monitors from running.
Also, the ez way to bleed the cooling system on a 5sfe is to remove the coolant temp sensor, The one on the upper radiator hose housing at the rear of the cyl head, it will have a green connector and takes a 17 mm wrench or socket, dint loose the copper washer. Fill the radiator until coolant starts to come out of this hole then reinstall the sensor and top off coolant.
Last edited by CWH5; 09-14-2010 at 12:17 AM.