Bob's Resource Website (2007)

Core Plugs, freeze plugs

Don't let the replacement of these plugs intimidate you

This job was performed on a 55 Sedan. The 55 and earlier engines used a different style plug than later engines, as there is a land behind the plug which the disc locks into. Later engines have the 'cup' type plug. I believe that both sizes are 1 1/2 inch, but if you use the rubber type, as a replacement on the early engine, you must use the 1 1/4 inch size to clear the land

A Hawk has as much or more room underneath

An Avanti can be difficult to work under, but you can get it done with some patience and determination

Jack the car up and place stands under the axle or forward frame rails. A good idea would be to leave the floor jack supporting the center pin. Removing the wheels helps.

You'll need some special tools ( see below) and a good thing would be a small plastic tub which you mix concrete in.

You'll need 6 plugs, discs or stoppers, whatever you want to call them. However, if you only buy 6, then you're bound to screw one up. So get 7-8 if you want to do it right the first time and if you're doing the Dorman DC9 plugs or the metal discs, get a tube of RED LOCKTITE
Dorman DC9's cost around $3.35 ea, the rubber ones $2.50 and the metal discs around $0.35 ea

Drain the radiator / remove the starter / place the tub under the one side of the engine / remove the rear block drain plug

After draining the block, remove the core plugs by centering the punch and giving it a good smack with the hammer. You're trying to break through the plug a bit and then use the punch as a pry bar to twist it out. Once the seal is broken, it may just fall out. . Be CAREFUL to CENTER the punch, so as. to not damage the lip of the block or the land on earlier engines. Also, don't drive the punch in more than an inch or you can contact the cylinder wall on a couple of the cores.


    1) After you've removed the plugs, if you don't have to clean the inside of the block, dry things up, clean each core hole WELL by scraping the outside free of grease. Clean the entire area, well, with alcohol, including the inner lip, if you have one

      Dorman plugs:
      • Hand tighten the acorn nut on the Dorman plug, Use a MARKER PEN to draw a reference line from the tip of the nut down to the flange on the plug. This can be used as a reference to tell you how many turns you've made when tightening.
      • Put a bead of Locktite around the edge of the plug and insert it into the hole. NOW, you have to leave each plug set for 20 minutes to let the locktite gel. How you hold it in the engine is your choice. Usually you can wedge a piece of wood or a rag against it and some other underside component.
      • After the set up time, tighten each acorn nut 2 turns ONLY
      • The engine should be allowed to set for 24 hours for the Locktite to cure

      Rubber Plugs:

      • Remember the later engines use a 1 1/2" because they have no inner land, just check to make sure
      • The rubber must be absolutely dry, so wipe with alcohol and allow to dry
      • Begin by snugging the nut up to the top washer. Draw the reference line across the top as stated above. Insert the plug into the hole and force it in, until the outer disc is flush with the block. Again, the early engines will be using a plug which is slightly smaller than the actual core hole because of the land. In later engines, the plug is the same size and the outer disk will snug right into the hole.
      • Tighten the nut 2 turns ONLY
      Metal Disks:
      • Again, the area must be absolutely clean
      • Place a bead of locktite around the circumference of the disc
      • Set the disk in the hole with the concave side facing inward. Place a band of masking tape across the disc to hold in place
      • After 20 minutes, using a tool similar to the pry bar, but with a ROUNDED point, center on the disc, and give one or two solid raps to force the disc to expand into the core hole.
      • For the uninitiated, the metal discs are somewhat troublesome to set, but they are cheap and easy to work with
      That's it!

      If you have to clean out the block

      A few tools which I used in the process. In addition, get a couple coat hangars and create some small picks and scrapers.

      On a Sedan, you actually have the room to access all the plugs. This car is raised about 18" off the floor and has the starter and front wheels removed

      To remove the old plugs, just position the sharp end of the pry bar on the center of the plug and sharply rap, until you break through the plug. When the bar is in about an inch, you can pry the plug out if it hasn't already fallen out.

      You'll be greeted with some kind of crud behind the plug

      Don't be surprised if the pipe plug twists off and is corroded up to the head, leaving a dam of rust jam in the hole. The alloy in the Stude Block has a lot of nickel and does not rust easily, but everything else does.

      You have a choice of replacements, including a plain steel, concave disc, which is what you removed, a rubber expandable and the Dorman DC9, expandable copper unit

      This is the Dorman DC9

          The rear has a tightening disk which snugs the plug in the block

          The latest NAPA number I have is NAPA/Balkamp 600-4027 or Dorman 568-009.

      With your tools, poke around inside the inner core as best as possible and flush repeatedly, allowing the crud to drain into the tub

      Cleaning out the block is very important, although, not the point of this page. It is a dirty and tedious task, but will provide a much cooler running engine

      Make your own tools to clean the block. A coat hangar, formed into various curved, pointy and hooked devices, along with small brushes are your best bet. The brushes can be rifle barrel cleaning types.

      Remove the upper hose, thermostat housing and thermostat
      Stuff part of a rag down into the thermostat housing and with a screwdriver, force it into into the water manifold run, opposite the side of the engine that you're working on. ( Leave enough hanging out to pull it out later)
      Using a large neck funnel, jammed in the thermostat opening and pour a half gallon at a time. The flush will drain out into the concrete tub. You may want to block the front two core holes initially to allow the rearmost one to get more of the water, as that is where most of the crud will reside because of the angle that the block sits at.

      Scrape and flush as many times as you can endure. You can't do a bad job here

      One other thing...after you're finished with this entire job, it's recommended that you use a heavy duty cooling system cleaner to rid the block of the remaining rust and contaminants.

      Fill system with water, including the heater circuit. Pour in a couple cans of Prestone HD Flush, Drive the car 10 miles, drain, flush, drain, flush, refill with antifreeze and water

      Note: For cars that are only used in the warmer months, water is a much better heat exchanger than a mix of anti-freeze and water. Using plain water with an OTS additive to prevent rust, for the driving season, then draining the cooling system for the winter over, can save a bunch of $$$.

Also see The parts sheets

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