So I’ve already installed the new radiator but it got dark before I could fill it up with coolant. I’d read a post yesterday by somebody, can’t remember who but I think it was DiscoMike, that made mention of running distilled water through the radiator, getting the engine warmed up, flushing water and THEN adding the coolant.

Is this the correct way to do it? I assume that the water is to flush any debris out before the coolant goes in since it can be caustic.

Just want ant to make sure before I finish the job up tomorrow. Would hate to screw something up and have to replace another leaking radiator.

 

I always pre-dilute my coolant and then just fill up. If you want to flush the block at the same time, that's a good idea, but you don't need to run the engine to do that. Since your radiator is out, your lower hose should already be disconnected. If it's not, disconnect it. Then pour water into the upper hose until the fluid coming out of the lower hose is clear. Then pour diluted coolant into the upper hose until the liquid coming out of the lower hose turns green. That will flush out the block.

Once you're done with that, reconnect all your hoses and fill up the system. Follow the proper bleed procedure if you're running a factory setup.

 

You would want to do such a pre-flush if you were changing from dexcool to the green coolant, since the two don't like each other. Flush remnant of old out, then add the new coolant.

If no coolant change, then not necessarily needed, although if the old radiator had a lot of buildup internally, there could be some benefit to flushing out potential particulates.

 

DM may have been thinking of residue left inside a new rad during the mfg process.

Normal tap water is fine for flushing. Distilled water is recommended when using 100% coolant to dilute it to 50%. Minerals in the tap water don't instantly drop out and clog your cooling system.

Running engine with water as a flush then draining before refilling is a good idea. While the engine is warmed up to operating temp the water will do a better job of cleaning/flushing. Remember mother telling you to wash your hands with warm water or washing the dishes with it hot.

It's another step that may not be necessary but if **** like me you may want to consider.
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