Is there any special maintenance with an aluminum radiator? I've been told there not good for cars that sit alot.
I have a water pump leak which has drained the coolant a bit so don't be alarmed that you do not see coolant. The coolant is Prestone and pours out of the jug yellowish. I don't remember the exact type.
Here are some pics of the "stuff".

http://www.renaissanceracing.com/images ... pStuff.JPG
http://www.renaissanceracing.com/images ... Stuff1.JPG
http://www.renaissanceracing.com/images ... Stuff2.JPG

I plan to change to Zerex G-05 Phosphate free when I change the engine. Is this a good idea?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

I don't know what it is, but the same thing happened to my 70 when it sat for a year before I pulled the 383. The water pump impeller, aluminum radiator, and cap were all coated in it. Nasty stuff.

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70 Dart, 360, 727

Maybe that white crap is from electrolysis. Two different metals ( aluminum radiator and an iron engine) using the coolant as a conductor might cause it, I would guess, and heat from running the engine would speed up the chemical reaction with the added heat. Maybe switching to distilled water might help since it is impurities in water that conduct. Thats my guess. To clean it, drain the old coolant, flush the system, then refill the system with water and add the same amount of dishwasher detergent that you would use in a home dishwasher and run the engine for a while, drain it, repeat with the dishwasher detergent then flush it till the detergent is gone. Thats how you clean saturn cooling systems which have an aluminum radiator and an aluminum engine. I've owned several saturns over the last 15 years and never seen one with that white crap though but the only steel in the cooling system is the water pump impeller.