The Stovebolt Site Forums The Shop Area Engine Shop Best way to flush an engine block.

Hey all, I bit the bullet and ordered a new radiator for Gertrude (61 C10 w/ 235 and a 4 spd). I am going to replace the thermostat and rubber hoses while I am doing this as well.

What is the best and safest way to flush the block? I don't want to harm anything or, worst of all, leave deposits behind that will damage my new radiator.

Also, should I change my water pump since I am digging in this deep?

The only issue that made this necessary was the leaking factory radiator, so no other issues were presenting in the cooling system.

Thank you,

Kyle

Was the water rust color or rusty? If not I wouldn't think there would be a need to flush the block with anything other then just plain water. Its a good practice to replace the water pump, thermostat all the hoses and belts along with a new radiator.

CLR or Muratic Acid. Flush with baking soda to neutralize and then lots of clean water.🛠

I just used CLR to try to clean some crud out of the rear part of my 235. One of the warnings on the CLR bottle is "don't use on brass, copper or aluminum." Your head gasket could (like mine) be the copper sandwich type and your radiator is either brass/copper or your new radiator could be aluminum. Some of the new ones are. Muriatic acid and aluminum gives off hydrogen gas plus muriatic acid can and will dissolve aluminum.

I've been trying to figure out the best acid to use as a lower block cleaner (engine not running), but I haven't gotten much guidance yet. Hopefully somebody here knows the answer.

Good luck.
Jon

Try vinager

I thought about vinegar, Bob. But it would have to be much stronger than common kitchen vinegar, wouldn't it?
Jon

You can get 20% industrial vinegar which is quite a bit stronger than the grocery store stuff. The wife has some she got from the garden store (used to kill dandelions). I can tell you it sure stings when it gets into a minor skin crack.

Thanks Kevin,
I looked around and found some that was 30%. I'm thinking this would be good in the radiator but I'm not certain it would be strong enough for the engine. I probably should have taken chemistry more seriously when I was in school. I know there is some acid out there strong enough to dissolve this stuff but don't know what it would be.
Jon

I'd try Hot Rod Lincoln, Jerry's recipe show here;


Re: Coolant temperature increase at idle [Re: Stove]
#1197596
30/12/16 05:55 PM

Hotrod Lincoln
There are two main cooling passage contaminants, and they respond to different treatments. I've never used CLR in a cooling system, but it's a good idea. I used technical grade Hydrochloric acid (muriatic) in the really rusty ones, 3 or 4 ounces of acid to a full fill of water and the thermostat removed. (no antifreeze) Run the engine with about half the radiator covered with cardboard to raise the operating temp. (Don't let it boil). Follow up with a fresh fill of water and a box of baking soda to neutralize the acid. Flush thoroughly and refill with a 50/50 water antifreeze mix.

For greasy crud, I use a can of drain-cleaning lye and water, plus 1/2 a cup of Tide. Circulate until hot, flush, and refill with water/antifreeze. Most commercial "radiator flush" products are far too weak to do any good. If the freeze plugs aren't new, be aware you might uncover some weak spots and cause seep leaks with this process.
Jerry