What would be the best way to replace coolant on LT1? It seems to me that there's always some of the old stuff left when I've tried.

 

drain it, fill with water, run it till the t-stat opens, repeat untill the water stays clean, then drain and fill with coolant

 

There are two plugs in the block (one is the knock sensor) but I found them too difficult to remove. I went the long way around but feel I got all the old coolant and debris from my LT1; here's the process I used:

Drain the radiator by removing the lower hose.

Pull the overflow tank from under the battery to be able to flushed it thoroughly.

With care, place rags around the thermostat housing and over the part of the optispark you can get to. Remove the thermostat from the engine; I think you can leave the top hose connected to the outlet. With a garden hose and spray nozzle I continually sent clean water into the block from the top and watched it as it came out the disconnected lower radiator hose until it was clear.

Remove the two heater hoses from the heater, put the heater control to open and send clean water through one fitting until clear water comes out the other. Connect an appropriate hose, several feet long to one of the heater core's inlet/outlet connections and push clean water through it until clear water is coming through the heater core. You may wish to reverse the connections to make sure clean water comes out in both directions.

Flushing water through the radiator with the hoses disconnected is obviously important. Reconnected the lower hose when the radiator is clean and fill the engine block through the thermostat housing until it will take no more water. A lot of gurling will go on as the block fills a little slowly. Then connect the top hose and heater hoses.

Fill the radiator and overflow with the appropriate amount of antifreeze (one gallon) and top off with water. Begin purging the air from the system through the two air release fittings. The rest is just checking levels, looking for leaks and re-testing for air through the air release fittings.

I know this is a lot of work and time consuming but I'm fairly certain it gets all the old coolant out.

 

Thanks a lot. That's exactly what I meant: not the easy way but the one that got me rid of the old degraded coolant.

 

You are welcome and I hope what I typed is all correct. It's been a few years since I did it to my coupe. BTW, if you are new to the forum, it's nice to have you here.

 

I use distilled water mixed with antifreeze; the tap water here in CA is full of minerals.