I want to toss something in there that will help flush out the rust.

Any ideas? Parts store is closed and I'm impatient. I need something to fill the system with (along with tap water) and let the engine churn it up before draining it again.

Think CLR would work?

That doesn't sound like you, it might work but I'd wait. The best flush that ever seen/used was a two part grainular (acid and neutralizer) by dupont, I haven't seen it available in a long time though. The last time on my DD I used prestone HD.

Try dishwasher soap.

Since you are impatient, I am probably too late, lol, but CLR is the only household product I would even consider.

I decided not to since it says it doesn't play well with aluminum or copper.

Also I can't drain the passenger side of my block because the drain hole where the knock sensor is doesn't go all the way into the coolant jacket.

I've considered drilling it...

I have used "Purple Power" soap to flush out a cooling system before.

When we bought our Jeep Cherokee it had a cracked radiator and the PO had filled it full of stop leak which inturn also stopped up the heater core.

Purple soap and a little flushing after I let the fans cycle a few times cleaned it right out.

Note I ran it with purple soap in the old radiator first. Then ran it with the radiator completely disconnected and the lower hose attached to the water hose until the water comming out the upper hose was clean. Then back flushed the heater core with the hoses disconnected. Then installed new radiator, and filled with distilled water and antifreeze. Over 3yrs now and everything is working fine.
Will

Quote:
You might check again. After all, those are the block drain holes. In the days before knock sensors I had one that wasn't open to the coolant, I thought. With the plug out it was as dry as a bone. Finally, I took a small screw driver and with it against the bottom of the hole, I hit it with the palm of my hand enough times to break through the build up of rust and sludge. It felt as solid as a rock until I got my bath of antifreeze.

RACE ON!!!

No, it's solid metal. You can also clearly see the circular groove marks from whatever tool they used to drill it or cut the threads at the factory.

I guess a few little metal shards in the cooling system won't hurt much. Maybe if I drill it with that water behind it, any metal chips will be forced out by the flow.

It's the one part of my engine that doesn't leak, lol.

No Surfactants and nothing that attacks aluminum or else you'll be doing the Heater Core very soon.

I've probably flushed my rusty system 6-8 times since I did the water pump and Radiator.

PO had the system so clogged that the Heat didn't work when I got it......Now it works like it supposed to.