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2005 Grand Prix over heating

I have replaced the radiator and thermostat on my sons 2005 grand prix. It has about 95000 miles and it would seem the previous owner(s) did nothing to maintain the cooling system. After flushing the system four times the car still over heats. After the car is parked it will boils so much coolant into the overflow that it then overflows that and onto the ground. The “coolant” that was flushed out was very heavy with sediment even after four flushes. The car has the standard 3.8L. I could use a tip on what to look at next.

The vehicle came from the factory with GM’s high mileage coolant called Dexcool. The problem with Dexcool is, if the cooling system isn’t maintained where air is allowed into the cooling system it turns the Dexcool into a gel and becomes acidic. This acidic gel then starts to eat into the cast iron engine block, head gaskets, and intake manifols gaskets. That’s why you can flush the cooling system forever and never remove all the sludge.

If you keep overheating the engine damage to bearings and rings is going to occur. But if you want to try to save the engine, the intake, heads, and frost plugs need to be removed in order to flush all the crap out of the engine.


Is there no way to get the Dexcool sludge removed? I have one person that suggested a product called RMI-25 be placed in the coolant and it will loosen up the sludge. I have a 2004 Monte that has had various leaks and those have caused the coolant to turn to the brown/red clay looking stuff that seems to be everywhere.I flushed it out at 45K, now at 89K, when the belt tensioner had a coolant leak, yes the belt tensioner has coolant running through it for hose routing reasons. Now I am replacing lower intake gaskets and the belt tensioner elbow seals. I would like to finally be rid of the sludge if anyway possible.