the laundry detergent is used when you have the oil cooler milkshake. flush it, then run it for a few days with laundry detergent to cut the grease and hopefully deposit it in the overflow tank.
On the dark side - ZZZ M Roadster
Past Porsches: Velvet Red 89 951 (51k mi, sold 6/09) UberRareRed 90 S2 (73K mi, sold 11/08)UberRareStolenRed 89 S2 (73K mi stolen 9/03), RareRed 88 951(The Duck's) StoneGray 89 S2 (Shouldn't have Sold to brother), Linen 89 NA (Was my brother's)
I've dealt with a clogged radiator in my '87, and I had fairly decent results by using "The Works" brand toilet bowl cleaner.
You need to remove the radiator and either usurp the kitchen sink, or use a "deep sink".
Start by blowing low pressure air through the radiator fins to remove any bugs, road debris, dead cats, or other obstructions. Flush the radiator internals with clean HOT water, and then drain the radiator. As you flush the radiator use the palm of your hand to check the temperature of the cooling fins. Clogged cooling tubes will be cooler than open tubes. This will give you some idea of how badly the radiator is clogged. If more than 1/3 of the radiator is cool, cut your losses and by a new radiator.
If less than 1/3 of the radiator is clogged, add some cleaner and just enough water to almost fill the radiator. Carefully tip the radiator from side to side so the solution gets mixed and then set the radiator aside for several minutes.
As the cleaner does it's thing, the chemical reaction will cause some bubbles and foaming. Periodically tip the radiator from side to side to "stir" the cleaning solution.
Once the chemical reaction slows/stops, drain and flush the radiator, and use hot water to check for blocked tubes.
Repeat the cleaning process as necessary.
Note: This particular cleaner contains Hydrochloric Acid. Wear eye protection and rubber gloves. Clean any spills immediately. This product will also "bleach" the plastic side tanks.
I used this process on the radiator in my '87. When I started the car would overheat at the drop of a hat. I borrowed a used radiator so I could expirement on mine. I tried the "normal" radiator flush (Prestone), CLR, vinegar, and several other concuctions with little improvement.
i haven't actually used it yet but i bought some zerex super radiator cleaner. does it really matter if it's aluminum safe? i didn't read the bottle that carefully but it's not in the car for very long so unless it's super corrosive and actually eats away at the engine, i imagine you'd be ok.
Be careful on what you stick in the cooling system. Dish washing soap like Dawn works fine to cut out oils and such. But powdered dishwasher soap like Cascade will be a disaster as it eats up aluminum. Just come over and take a look at my aluminum garlic press - it is really a mess from just one cycle in the dishwasher and Cascade.
I'm not sure how vinager would do to remove the hard water deposits. Probably not too good because you can't scrub the deposit. One of the metal guys could give a much better idea on how to approach. I just used the Prestone quick flush and it seemed to work OK and not damage things. Engine runs cool at ~ the first hash mark.
I'd say that liquid detergent or degreaser (SImple Green or any of the purple stuff) would be best to get any oil out of the system. It's good at breaking down oils and shouldnt get all foamy like I imagine dish soap would.
Vinegar is an old trick for cleaning hard water and mineral deposits from your coffee maker. Aslo good for soaking your clogged shower head.
But is a lot of the radiator build up from hard water or it it some kinda corrosion or electrolysis build up?