(Text by Gene Gillam and John Seim, Photos by Gene Gillam)

I’ve been plagued by my TC running hot ever since I restored it and, while going through the archives I found an email from David Edgar on the subject of overheating in which he said there was a big revelation about 10-15 years ago concerning a 3/16" diameter passage drilled behind one of the freeze plugs. The hole is directed down and aft which allows the water to flow to the back of the block to increase cooling in that area. Apparently over the years the small hole plugs up and the water flow stops. John Seim mentioned in this same thread that later engines had this hole drilled in both core openings. The hole was either for cavitation purposes, or the factory found that one hole was not sufficient should it become plugged.

I emailed John and asked if he could guide me in finding and opening these passages. He provided the following:

Remove the two small core plugs on the carburetor side of the engine, in the raised casting area. There are three plugs above these two, in the block, and two below the raised area, in the block.

The rear plug should have a 1/4" - 9/32" hole, in the back bottom portion of the casting, extending downward at 45 degree angle. Use a punch, nail, or other probing device to locate this hole.

In the photo above you can just see the outline of the hole near what appears to be the center of the freeze plug area. This is an illusion caused by the photograph – the actual hole is located in the bottom of the casting as can be seen by the photo where it has been drilled out to 9/32". The photo below shows the hole after a small round file has been pushed through it to open it up.

Once located you can then use a drill to clean out the hole. This photo shows the true location of the hole and how it looks when it’s been drilled out to 9/32".

Duplicate this hole in the forward core plug. Angle the drill down 45
degrees. Don't worry about going too far, you will find it tough going
until you pass into the inner block water jacket. Then you can stop.

Before

After

John also provided the following in regard to installing new freeze plugs and other hints to reduce overheating problems:

Make sure that the seating surface for the core plug is flat. Use Permatex #1 or 1B, along with the core plug. I used to use a two ball peen hammers. One, about the correct size of the core plug. The second, to hammer against the other hammer, held hard against the core plug. Do not over drive the center of the plug. I have since made a hammering
piece, to hold against the core plug. This is slightly smaller than the seating area for the core plug. (NOTE: a 1 1/16" socket will also work).

When all is done, you should be running at most 70 C. My car runs 142-156 degrees F, in Southern California. You also might want to look at the distributor. There is supposed to be a phenolic washer between the drive gear, and the housing. Total end play .006"-.009". Too much play, and the distributor retards as the engine revs. The gear moves up the cam gear, thus retarding the spark. You might want to remove the water pump, and run a coat hanger along the left side of the engine (side opposite the core plugs). You should be
able to run a coat hanger through the water pump opening, all the way to the back of the block. This will clear a blockage that you can't get to otherwise.

Hope this helps.