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I have been digging chunks of crud out of the '55 352 while I have it on the engine stand. I popped out all the freeze plugs and the old dried up gunk in there is pretty bad.

I was on a HotRod forum recently and one of those guys mentioned blocking off all the holes in the block and filling it with some CLR and rinsing it out with water. He claimed it would eat up alot of the deposits and help get it all out.

The engine was a runner, and I don't want to take it apart and have it tanked unless I absolutely have to.

Any thoughts on this?

Link to what CLR is HERE

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I have used it for it's intended purposes and frankly, was not that impressed despite the stars in the ratings. The FAQ does mention that it was not recommended on the car as it might contact aluminum or paint and is not recommended for cleaning radiators or cast iron due to metal reaction.jelmar.com/faq.htm

portlandon, some years ago I had a '39 Cadillac 60 Special (L-head V-8). I had the engine in the car, but the block was stripped of all accessories and equipment. The water jackets had heavy deposits of rust and gunk. After power washing the jackets as good as I could, I blocked off water passages and filled the system with a light solution of Drano. It was successful in ridding the system of more rust and gunk, and a nasty greasy residue. I did not leave the Drano solution in the engine very long and thoroughly rinsed it out. I think if you are careful you can use something like this. It worked for me. Of course, the best thing to do is have the engine block dunked in a cleaning solution by an engine rebuilder. I had the cylinder heads dunked since they were off of the engine. My thoughts.

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Is the main ingredient in Drano lye? or is that Liquid Plummer?

Believe both. Think Drano is mostly lye and Plumr has some other stuff as well so it thickens & sinks.

If the head(s) were still on the motor, I would be concerned what the lye may do to the head gasket(s). I also find that while lye based cleaners works great for cleaning out thick deposits of gunk and grim and things like that on parts, but the metal will quickly flash rust afterward if not completely rinsed clean and force dried.

I dont think lye is a good choice on aluminum.

Thanks for all the responses. I don't think I'll be using any of these chemicals in the engine.

I will try using a pressure washer and getting out as much as I can. I hate to tear it all down if I don't have to. I was just going to paint it, but decided to replace the freeze plugs, but glad I checked. It was full of gunk.

Thanks again fellas.

Lye (sodium hydroxide) is sold commercially in liquid form as a 50% solution, and packaged in plain steel drums so there is no need to be concerned about lye attacking cast iron or steel. But it is RAPIDLY and QUICKLY destructive to aluminum. A strong, warm lye solution can eat thru 1/4 inch of aluminum in minutes; in fact that's the basis for the alternative to machining on reducing the weight of aluminum parts, so called "chemical machining". OEM headgaskets for the V8 were steel shim so that shouldn't present a problem.

I still think the best common chemical to use for rusty systems that's safe on other materials is oxalic acid which can be bought in most hardware stores. It can solubilize ("chelate") iron oxides; but use a neutralizer like baking soda afterwards. I think we've covered the use of oxalic acid in the past on this site - a search might be beneficial.

Some years ago (20?) a neighbor who worked for Peak gave me a product called Peak Purge. It was a cooling system cleaner that was organic and biodegradable, safe for aluminum. Wow did it clean beautifully.

You could toss it in the radiator, drive 100 miles and drain the system and watch the crud pour out.

I can't find it these days; does it still exist? Strikes me it would be excellent for old cooling systems because it got both rust and the whitish crud that collects in radiators (calcium?)

Anyone?

There are several "radiator flush" products on the market...Prestone, DuPont etc that are safe for most metals. I usually add them in the recommended amount and drive for several miles and then flush, refill with fresh water, drive and flush a second time before refilling with antifreeze.

A lot of crud comes out after the first and second flush. Also, drain by removing the lower rad hose as opposed to the drain-cock....lets the big chunks flow out better.