The directions on the coolant flush say drain the radiator and add flush + water.

I've drained the radiator and the block, so now there's nothing in the block and the radiator is filled with water and flusher. I put some water in the coolant reservoir too. There's no antifreeze anywhere in the system.

Is it really ok to run it like this?

 

I wouldnt do it for a long time water will corrode your cooling system.
I have done it in a pinch but I typically take it too a lube shop and have them vaccum extract the old and pump in the new, make sure they have the machine. its really cheap under a $100 bucks and you dont have to mess around with coolant and wonder if you got all the water crap out.

Also its spring time so your ok for a little while if it was winter you would not last the night

 

For a flush and refill, it is fine.

 

If it were winter and he were running the vehicle, then it would last all night no problem.

Water isn't that big of a problem, for a while, and a while means days, not minutes



Fred

 

Yes, the flusher will prevent corrosion, and loosen any deposits. Run it for a day or two, then drain it, refill with water, run it for 20 mins, then drain and refill with 50/50 coolant+water mix.

The main concern with 100% water in an engine is not freezing, but rather, corrosion. Remember how a battery works, different metals + electrolyte. Galvanic corrosion is a serious problem. Driving for as little as 1 week can turn your water in to brown rusty goo.

 

I've definitely run too little/no antifreeze in the winter. It's really fun having your cooling system frozen.....not.