99 Montana overheated - replaced frozen thermostat now have MIL and steam from right air bleed port

bighank1bighank1 Member Posts: 31
edited January 2016 in Pontiac
Car overheated and pegged temp gauge at 260F. Replaced thermostat and temp sensor and ran engine. Left off the upper hose clamp to see what coolant looked like after thermostat opened. Had Dexcool sludge in radiator at cap and wanted to flush radiator and engine.
Drain cock on radiator broke as I tried to open it. I tried to remove it with pliers but more plastic snapped off. Tried closing it and went on with test of car with new thermostat and temp sending sensor.
Filled radiator with water and started engine.
Thermostat opened partially after a few minutes. Took upper radiator hose off of thermostat discharge pipe and saw brown colored coolant spitting out.
Added water to radiator with garden hose to replace the coolant running out of the thermostat pipe. Temp gauge was working and went up to 4 marks past 210 printed on gauge. I guess it is about 230 degrees F. SERVICE ENGINE SOON light blinked on and off and then came on solid.
Shut off engine, removed plus lead from battery to reset the MIL indicator and put upper radiator hose on with a hose clamp to the thermostat pipe.
After about 15 minutes restarted engine and attempted to bleed out the trapped air in the system. Left bleed port above the water pump released air and then sputtered coolant. Right bleed port on thermostat pipe going to upper radiator hose spit out steam for several minutes. Finally it sputtered a small amount of coolant then went back to solid steam. Expected some air but not 5 minutes of steam.
SERVICE ENGINE SOON (MIL light) is on solid again. I thought that removing battery voltage for 15 minutes would reset the MIL status.
What do I have? A blown head gasket?
No evidence of coolant in oil or exhaust. Temp in the 30s outside. Saw some exhaust plume but not steam.
Was going to flush system to get rid of Dexcool sludge in radiator and engine but not sure if engine not blown. Have about 110k on the engine.
What do i do next?


  • Mr_ShiftrightMr_Shiftright Member Posts: 64,482
    One thing you can do is scan the car's computer to find out what codes are being stored. You may want to pressurize the cooling system to test if you have in fact an intake manifold leak, which would cause an oil/water mix and consequent sludge. A pressure test can also be used to test head gaskets, as you can extract the spark plugs while the pressure is still applied, and check for coolant or water on the spark plugs.

    You can also test the coolant chemically for combustion gases using a simple kit you can buy at Autozone or some such.

    Dexcool sludge can be pretty stubborn to flush out, so if you have no intake manifold leak, no head gasket problems, then probably a new radiator is in order.
  • bighank1bighank1 Member Posts: 31
    Reverse flushed radiator by taking off lower hose and using a garden hose and an compressed air line.
    Had upper hose off of the pipe that goes to the thermostat. Got good flow and clear water coming out of the upper radiator pipe.

    Reconnected hoses and poured in almost a gallon of fresh antifreeze. Started car and used the 2 bleed valves to get air in the system out.

    In about 5 minutes temp rose to almost 260 even though get no heat from front or rear heated.

    Even though there is no evidence of coolant in the oil suspect blown head gasket.
  • Mr_ShiftrightMr_Shiftright Member Posts: 64,482
    You should be able to spot combustion gases in the coolant by using a chemical tester you can buy at most auto parts stores.
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