I just had my engine sent out to a machine shop, they did my 2.1 stroker install, hot tanked the block, all new bearings, freeze plugs, and painted it. I have my engine all back together and I'm draining coolant out of this plug in the back of the engine right underneath the intake manifold (below the main coolant hard line that goes to the water pump). Its diagonally decending from the freeze plug on the back of cyl#4 toward the passenger side of the car. This is the best picture I'm able to take with my cellphone and a mini led light. Any ideas on the size of the plug would be very much appreciated as I cannot find ANYTHING about this anywhere on the web. I tried to size it up with a spark plug and its just a hair bigger.



Thanks,
C

 

Bump. I found the OEM Mitsu Block Heater is part # A993FH1X01, but they do not list sizes, and this is where it would go to heat the coolant.

 

Hmm, looks like it might be 35 mm.

 

Thats the freeze plug bud. The black hole thats 1/2 the size. Come on?

 

3/8 npt thanks to brian gleason @ stmtuned