I'm looking to overhaul the cooling system of my '96 (replacing everything except for the heater core). Originally, my plan was to drain the coolant, flush the radiator, block, and heater core independently, run a chemical flush through the whole system, and then replace everything. Would using the chemical flush have much benefit in this case or should I skip it an just drain and replace?

 

Depends on what it looks like in there.
While I never used it I always figured I would use this stuff.


Reason being is I use their Evapo-Rust to remove rust off of smaller parts and think the stuff is amazing so.....

 

That's what I used when I did my cooling system overhaul. It really got the inside of the engine looking good. If you're not replacing the heater core, I'd bypass it before running this stuff just to keep all the crud out of the core. Don't worry about the radiator since the passages are bigger and you're replacing it anyway.

 

If you can take the time to remove the intake and exhaust and replace the freeze plugs, that is far and away the most effective thing you can do to remove rust. Flushing from the water pump or thermostat outlet is good, don't get me wrong, but you just don't get enough flow at the back of the block to lift up any rust debris that's settled. I've opened them up on two 4.0 motors that got major flushes beforehand, both still had a ton of junk in them.

In an ideal world, I'd plan on flushing the block, removing the freeze plugs and manually cleaning out as much as you can, replace plugs, flush the block and radiator again, and then use chemical flushes or treatments. If you want to install the new radiator in that process, I've heard of using a piece of pantyhose pushed into the radiator and held in place by slipping it between the radiator hose and radiator fitting to catch any rust flakes before they get lodged in your new rad.

 

Thanks for the great idea on the freeze plugs. Do you use a hose to spray out the holes where the freeze plugs go? Although the job doesn't look too terribly difficult, I'm thinking it might take me a few days. Is there any issue leaving the engine drained of coolant for a day or two? I'm worried about it rusting.

 

No issue with leaving the plugs out for a while. I guarantee you that the block is already quite rusty internally, and you won't get it perfect.

I started by using my hands to grab as much goo as I could, just to see how much there was. Then I sprayed it out with a hose. Then I used steel brushes, including rifle bore bruses, to scrub as much of the cylinder wall as I could reach, which wasn't much in the grand scheme of things.

Below is what I got out of an engine I ended up scrapping because it was just so beat up. This is after flushing it on two separate occasions.