C2 coolant change

[Kevin B.]

I am in need of replacing my old, worn out heater hoses on a 1966 327cid, no A/C, P/S. There is no radiator cap, only an overflow tank. Do I use only the overflow tank to fill the coolant system? Is there an engine drain plug for the coolant? I have a 1966 Chassis Service manual but, strangely, there's no procedure for a basic coolant / heater hose change. I am concerned about not getting all the air out of the engine and possibly running on too little coolant level. Any advice appreciated.

[Joe L.]

Re: C2 coolant change

I am in need of replacing my old, worn out heater hoses on a 1966 327cid, no A/C, P/S. There is no radiator cap, only an overflow tank. Do I use only the overflow tank to fill the coolant system? Is there an engine drain plug for the coolant? I have a 1966 Chassis Service manual but, strangely, there's no procedure for a basic coolant / heater hose change. I am concerned about not getting all the air out of the engine and possibly running on too little coolant level. Any advice appreciated.

Kevin-----


The system is re-filled through the supply tank. In other words, the supply tank filler is used just like applications in which the radiator has the filler as an integral part of it.

The best way to drain the existing coolant is to open the radiator drain cock AND remove the block drains on BOTH sides of the lower block. This will provide for the most complete drainage of coolant. The problem is the block drains can be extremely difficult to remove due to corrosion. You don't want to take a chance on breaking the block trying to break these free if you find them "solid".

There is a convenient alternative. Buy a Prestone Flush-and-Fill kit (about 10 bucks at auto parts stores).

1) Drain the radiator, leaving the block drains as-is;

2) Install the "T" from the kit in one of the heater hoses, as described in the instructions. Attach a garden hose to the "T";

3) Install the "diverter" elbow and hose into the supply tank filler neck, as-instructed;

4) Turn on the water and flush the system until the water runs clear from the diverter elbow and hose;

5) Drain the radiator;

6) Fill the system with full strength coolant. Uusually, you'll be able to get in about 1-1/2-2 gallons which, with the water remaining in the block after the flush, will give you about a 50% coolant concentration;

7) If you don't want to maintain the "T" in the heater hose (with cap provided with the kit), replace the heater hose with the "T" in it and save the "T" for the next time.

[Duke W.]

Re: C2 coolant change

There are block drain plugs under the spark plug wire "boomerang" shields. You will need to loosen the shields and push them out of the way, but they do not need to be completely removed.

IIRC the block plugs are 9/16" hex 1/4 pipe threads. Who knows if these have actually ever been removed from your engine to fully drain the old coolant, so they may be seized.

Use a 6-point socket and a large breaker bar. Get a good grip and shock them loose. A 12-point socket can easily round off the hex of these soft steel plugs. DO NOT USE A 12-POINT SOCKET!

If no fluid drains or drains slow, dig out the debris that is blocking flow. This is common on blocks that have not been regularly drained by removing the plugs.

Once the block is drained and flushed reinstall the plugs with pipe dope, and just install them snug- no more than about 10 lb-ft torque. You can reverse flush the block through the heater hose connection on the inlet manifold and reverse flush the heater core through the exit nipple on the core.

Once the system is flushed and the block drains are installed and the radiator petcock is closed, slowly add two gallons of Zerex G-05 antifreeze to the expansion tank opening. When the antifreeze is expended, continue to fill slowly with distilled water. (The total system capacity is about 16 quarts.) Once the tank is about half full and will not accept any more coolant, bounce the car up and down with the bumpers and see if it will take any more to get the level up to half full. Repeat until no more can be added without raising the level about half full.

Manually open the heater flow valve or turn the control to full heat and start the engine with the cap off, and let it warm up at fast idle. Once the thermostat opens, the level should drop. Add distilled water as required to keep the tank no more than half full. Watch the gage to ensure the temperature doesn't go over 180. If it does, shut down the engine and let it cool before picking up the process again.

When the system will accept no more fluid without increasing the level of the tank to more than half full, install the cap and take it for a short low speed drive. Return and let the engine cool for at least a couple of hours, then check the level and add fluid as require to take it to no more than half full.

Check the fluid level again after it cools from the next couple of thermal cycles. The level in the tank should be about one-half full when the engine is cold. Overfilling the supply tank will cause expulsion of fluid through the expansion tank drain hose when the engine is hot or during thermal soak after engine shutdown.

Duke

[Kevin B.]

Re: C2 coolant change

Thanks! Both of your answers were what I was hoping to find. I thought it odd that there weren't any engine block drain plugs, but it's just that they were apparently hidden by the spark plug wire's shielding.

[Glen C.]

Re: C2 coolant change

Rather than start a new thread, does anyone have suggestions for removing the block drain plugs on a 66 BB? Mine has the drain plugs that have an indented square hole the size of a 3/8" socket extension. They won't budge! I haven't tried an impact wrench yet, would this be recommended? I'm not sure if this type of plug is correct for a 66 BB, please advise. Thanks, Glen.

[Ronald L.]

Re: C2 coolant change

Here is the link to removing drain plugs, impact, heat & drilling...

https://www.forums.ncrs.org/showthread.php?t=81778

[Glen C.]

Re: C2 coolant change

Here is the link to removing drain plugs, impact, heat & drilling...

https://www.forums.ncrs.org/showthread.php?t=81778

Ron, Thanks for the tip, I'll check it out. Glen