How to install a freeze plug heater (Block warmer)

Thanks to 1-5-0 SHO for submitting this article

How-To: install a freeze plug heater

This is how to install a freeze plug heater in your engine while your engine is in your car. I forgot to take pictures, but if you have ever changed your oil and drained the coolant this is not that much more difficult. When you put in your freeze plug heater, you will also be changing your oil and coolant.

This was done on my 93 ATX.


floor jack
2 jack stands
floor dry
1/2" wrench for disconnecting battery (most common size)
metric wrench for oil drain plug (size varies)
drain pan for oil
drain pan for coolant
1 piece of 3/8" heater hose about 1 to 2 feet long (not absolutely necessary if you are just going to put in fresh coolant)
small pry bar / long flat-head screwdriver
pliers for radiator petcock and freeze plug
a couple of empty jugs for storing drained coolant (2 1-gallon jugs will be enough)
course sandpaper
a dab of silicone (not absolutely necessary as coolant will work as well)
1/4" socket wrench w/ 8mm deepwell socket and 2"-3" extension
a couple zip ties

Parts & Supplies:

oil filter
5 quarts of motor oil
1 jug of coolant
35mm freeze plug heater (Checker Auto Part #10421 - $19.99)

1. Disconnect your battery with the 1/2" wrench. Don't forget this as you will be working near the positive cable on the starter.

2. Jack the front of your SHO up and put it on jack stands.

3. Drain the oil and remove oil filter. You may be able to just punch a hole in your oil filter, drain just that oil and remove the filter, but i suspect you will have a steady oil drip which will be directly over your face when you are installing the heater. When done draining, screw the oil drain plug back in and remove the oil drain pan.

4. If you want to reuse your coolant, put the heater hose on the radiator drain hole and the other end into the first jug. Open the radiator petcock so the coolant drains. Otherwise just drain it all out into a pan and dispose of.

5. Place a drain pan for coolant directly under where the oil filter goes.

6. WARNING! COOLANT SHOWER WILL FOLLOW! From underneath the front of the car, look up where the oil filter was. Just above and to the driver's side is the 35mm freeze plug. Use your hammer and small pry bar or long flat-head screwdriver and pop the freeze plug on one side until it flips sideways. When the freeze plug swivels in the hole, about a quart to half a gallon of coolant will suddenly gush out. Hopefully it all goes in drain pan. Any coolant that doesn't make it into the pan will end up on you. If the freeze plug doesn't just fall out, use the pliers to pull it out of the hole.

7. Once all the coolant has finished draining out of the freeze plug hole, take the sand paper and clean the hole, removing junk build-up and whatnot.

8. Now for the the freeze plug heater itself. Remove the rubber o-ring and put a dab of silicone around the rim where the o-ring fits. Now put the o-ring back on, and run another dab around the top of the o-ring as it sits around the freeze plug heater. The directions for the freeze plug heater mention that you can also use antifreeze for this as well.

9. Pop the freeze plug heater into the freeze plug hole. The actual copper heater coil part should point down and to the left towards the oil filter. Use the 8mm socket wrench to tighten the screw in the center of the freeze plug heater which collapses the flange on the inside that holds the heater to the block. This is the part that gave me the most trouble, as I had to use the flat-head screwdriver (by sticking it into the electric cord socket on the heater itself) to aid in holding it in place while I used the 8mm socket wrench to tighten it as the heater itself wants to turn and pop out if not held in place. The directions recommend 25 in-lbs of torque but I tightened it until I felt it pull snug and then some.

10. Run the power cord down from up top. Plug the end into the the freeze plug heater. Don't let the cord touch the exhaust for obvious reasons.

11. Use the zip ties to hold the power cord in place. I ran the plug-in end through the head-light socket and out through the grill.

12. Install new oil filter and add the oil.

13. Dump the drained engine coolant back in and add some more if it isn't enough, or just add all new coolant.

14. Reconnect the battery and start it up, watching so the oil light goes out and engine doesn't overheat. Take your SHO for a test drive, checking for leaks. If it you did it right you will have no problem.

15. Park your SHO and plug it in for the night.

16. Clean up and throw floor dry down.

17. Have a beer.

**NOTE: You can actually skip steps 1 through 16 and just go directly to 17, or do step 17 at any point you want.**