C2 Reverse Coolant Flush

[John L.]

I just completed a reverse coolant flush on my "66 big block using the Prestone Flush Kit which worked well. I ran the engine for about 10 minutes until just water was coming out of the deflector tube. After the engine cooled, I drained the water out of the radiator and slowly added Zerex GO 5 antifreeze with the cap off the T inserted in the heater hose. Once the level of the antifreeze in the radiatior was about 3 inches from the top, I ran the engine with the radiator cap off and heater on full, level of antifreeze dropped and I then added more.

I was able to get 11 qts of antifreeze into the system and the level is about 2 inches from the top of the radiator. Given the coolant capacity of the engine, I assume I am now at about a 50/50% mix of antifreeze and water, does this sound correct?

[Duke W.]

Re: C2 Reverse Coolant Flush

Check the AMA specs, but I think the coolant capacity of big blocks with heater is about 18 quarts, which would be about 61 percent antifreeze. The proper range is 50-70 percent for maximum corrosion protection.

It sounds like you didn't open the block drains. This is best, but if you reverse flushed with tap water you probably got most of the old coolant out.

If you believe the cooling system is in good shape, removing the block drain plugs and draining the radiator is all that needs to be done before adding G-05 and distilled water.

Flushing is optional, but if the block drains aren't clogged and if there's no evidence of junk in the drained coolant, it's really not necessary.

G-05 should be okay for five years on a car that only sees a few hundred to a few thousand miles per year.

Duke