Someone got a mechanic to do their passenger side freeze plug for $56.
I took off the exhaust manifold to do mine on driver side. Mine was next to the drain and there is another one under the power steering pump.(harder to get at).

Procedure
Open radiator cap. Coolant will empty out plug hole so place container to catch it.I used a 4 inch extension with the big end(female end) against one side of the freeze plug. I hammered with a small sludge hammer. It takes a bit of time before one side pops in and other side pops out. I then used plier to remove the plug. I hit the inside part not the rim. I then cleaned opening up with steel wool. The engine block part was not corroded.

I used a 24mm socket (32mm outside diameter) to hammer it in. it doesnt like to go in straight. Once I got it in a bit , I just used hammer and hammered the rim(all round) until it sunk in even with surface of engine block. This seemed to work well. I think this is all you have to do. I however continued hammering(with socket ) it in another 3 or 4mm. It was slightly crooked. I had to use a mirror to see it. a lot of the energy dissipitates because socket is hollow. A solid cylinder with larger diameter would probably work better. I did use liquid gasket maker. You will have to replace coolant and bleed system.

Types of freeze plugs
-steel- tend to rust. cheap a few cents or dollars each.
-bronze-harder to get in
-rubber-easy to get in. may pop out.

Tools
-pliers
-small sludge hammer 24lbs?
-large socket fpr pounding plug in
-4 inch socket extension to hammer out
-mirror
-flashlight
-container to catch coolant
-all the stuff you need to change coolant

Parts
-freeze plugs- get more than one as they tend to get damaged going in.
(The expansion(freeze, frost) plug is 40mm for the 1989-1998 240sx.(for the block) They mention a 30mm outside diameter one for the cylinder head. Not sure what that is.)
-liquid gasket maker
-maybe get a rubber plug for emergencies.

steel 40mm freeze plug

freeze plug again

My freeze plug next to coolant drain plug under exhaust manifold.
The freeze plug is recessed about 4mm into engine block. The picture is some kind of optical illusion.

Somebody elses leaking freeze plug

Link
http://forums.nicoclub.com/zerothread?id=136042
Coolant change
Exhaust manifold removal

http://www.automedia.com/Repla...1fp/1

old plug

Notes:

Modified by vancouverbc at 1:17 PM 1/14/2009

Modified by vancouverbc at 5:17 PM 1/20/2009

Modified by vancouverbc at 3:59 PM 3/27/2009