Scale on aluminum heads and in blocks.

[Gene in NC]

If scale builds up in engines using G---- stuff, What is process or chem to get it out. Prestone has cooling system flush in two strengths for iron blocks and heads. What works in our engines.

See my edited post below re 2 x over heat and radiator blocking in '89 525 to see why I'm a believer in scale as a problem that can strike without warning at the worst times.
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'89 525 has o'heated twice despite fair service on green stuff.

First on Christmas eve in NC mtns (Boone) 20 min. after climb through gap on r421 with no indication of above normal temp. Working against slight coolant loss following t belt chng 20k previous so I went for new w pump and t belt. After repairs shop fired up and it overheated right there from clogged radiator. $495 screwing for "new, brand ??" radiator that later couldn't be reblt/rodded out because end tank gaskets were not available. See below.

Second o'heat on nice spring day 5 mi from home on local freeway. CLose to time for another t belt so replaced eveything but USED ORIGINAL RADIATOR THAT HAD BEEN REBLT/RODDED LOCALLY.

All going well until I took out the water pump with over tight belt at 40 mos. Replace everything again but kept radiator. Green stuff looked really good after 40 mos.

Some source claimed that green stuff causes oxidation in block which under the right conditions will slough off and clog radiator. Been there done the twice. Even for a slow learner that is enough.

[gale]

I used 1 cup powdered citric acid (available in bulk from any pharmacy) and it did a good job & does not damage radiator/engine internals. All kinds of scale sh*t came out. After the flush, I did another neutralizing flush with baking soda before flushing again with plain water, & then used 50/50 BMW "blue stuff" & distilled water for the final coolant mix.

I ended up replacing the radiator later, due to cracks in the plastic sidetanks (not related to the flush). I was amazed at how much crap in the form of leaves, animal hair, etc. was trapped between evaporator and radiator when I removed it. I had blasted the evaporator & radiator with a hose & compressed air beforehand, and could not see any signs of the remaining crap before I actually removed the old radiator.

Now the temp gauge stays exactly at the 12:00 o'clock position and has been for several years since getting the new radiator.

[Hector]

noted that after the car had sat around for 8 months, there were lots of scales, rust and deposits in the engine block. I bought some stuff from NAPA that comes in a powder. You mix it with either warm or hot water and dump it in the engine and let it run for a while. Seemed to clean the engine pretty well as I could see a lot of crap that had been flushed out.