The DME opens the thermostat only when it deems necessary, if it can hold the engine temp where it wants with it closed it will do so. Maybe put the heater blower fan on the lowest setting so the heater core isn't acting like a radiator as much itself. I don't think the aluminum sediment is going to be carried in the flow enough to matter much, just the normal coolant flush will likely give as good of results as you can expect to get with the rest of the system intact.

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X5 pics

RIP 4.6is.....

2003 4.6is