View Full Version : Cool/Heat: 1955 Commander - Draining the Cooling System

07-15-2017, 02:44 AM
Hello all,

In preparation for removing the cylinder head to drill out a broken bolt in the cylinder head. First thing first, I went to drain the radiator. Shop Manual states the petcock valve is located on the right side at the front of the radiator and can be reached from below.

For the life of me, I cannot find it. I see a couple cut outs (one on the radiator support and the other on the bottom of the bumper) where I would think give me access to something, but the areas are too tight to get my fingers in there let alone a wrench or pliers. It seems too tight to access anything and I cant imagine it would be designed to be so difficult to find and/or access.


If anyone has any insight and/or pictures please let me know.

Thank you!

07-15-2017, 06:46 AM
Just from that picture, it looks like your radiator isn't original. If you can't access the drain valve, undo the lower rubber hose and let it drain that way.

345 DeSoto
07-15-2017, 10:26 AM
What HE said^^^^^^^^. I installed a Chevy-to-Jeep aluminum radiator in my Sky Hawk. Before doing so, I located the spot on the bottom of the radiator support where the radiator drain would be. I used the appropriate size hole saw, and drilled an access hole for it. I cut a wide slot in the end of a piece of EMT, bent it 90 degrees, and use it to open/close the drain. Also marked/drilled 2 more holes for AT oil cooler radiator fittings...

paul shuffleburg
07-15-2017, 11:39 AM
Have you checked the backside of the radiator
for the petcock?

07-15-2017, 01:14 PM
The Commander V8 Engine block will not fully drain from the Radiator, the Block Drain plugs have to be removed so that coolant does not go in the Cylinders and Oil when removing the Head.

You will find the block drain plugs on the sides of the block at the rear about 1 1/2-2 Inches above the Oil Pan.
The Left one is just above the Starter and if you go over the frame moving the rubber Inner Fender Mud shield up out of the way, you can see and access the Plug.

These Plugs if original are square and require an EIGHT POINT 7/16 Socket either 3/8" Drive or 1/2" Drive (Best) for a larger Rachet or breaker Bar, Universal Joint and extension to be used.

You can install Brass Petcocks in those holes for easier draining next time or New Hex Head, Brass Plugs that an ordinary 5/8" socket will fit. A little "Neverseize" on these will help with Rust prevention and removal.

07-15-2017, 04:35 PM
Sometimes it's better to sacrifice a freeze plug when completely draining the engine block than to try to remove those 60+ year old drain plugs....I've seen them break in half when forced! :eek::(

07-16-2017, 07:37 AM
Be prepared to re-tap those block plug threads! Luck Doofus

Blue 15G
07-17-2017, 10:04 AM
And if you do successfully remove them, don't have your face right under the hole(s) when you poke through the rusty sludge with a screwdriver! (BTDT.)

07-18-2017, 12:29 AM
Thank you all for the insight, everyone is always so helpful and non judgemental.

mbstude: I was worried about that, because nothing lines up according to the bumper cut outs. I think I will just pull the lower rad hose and drain from there.

StudeRich: thank you for pointing me in this direction, I would have never known. I slid under the vehicle just behind the passenger side tire and found this square looking leg. Is this the block drain plug you are referring to? A couple inches above oil pan. (pic attached)

doofus: you are always so helpful too. I got a tap and die set ready to go.

Blue 15G: thanks for the tip, I probably would have ended up learning the hard way if you didn't mention this.


07-21-2017, 09:37 PM

Radiator was drained from lower hose, however, the square block drain plug will not budge. I've soaked in PB Blaster and no luck. Should I apply heat to try and dislodge?

I have to say, I am very, very, very, very nervous to snap off the plug in the block as well. Maybe, I am not giving it enough oomph because of my apprehension.

The more research I do, the more horror stories I come across.

Thank you all!

07-22-2017, 02:48 AM
Just leave it alone and remove the Rear Core Plugs on each side.

07-22-2017, 06:44 AM
Kill two birds with one stone, with rear freeze plugs out you can now get really filthy gouging out the crud in the water jackets.L:uck Doofus