So, you want a tank style block heater in your VX? Problem:
Lower radiator hose feeds thermostat, not bottom of the block. Putting a tank heater inlet in this line would only warm the radiator. No good.
There is no other low point to connect a tank style heater other than a very large, very fine threaded, block plug. It is 34ish mm with a 19mm head.
Here's my kit:
Tank heater kit including a 5/8" T, clamps, and nipple. You'll also need about 8' of 5/8" heater hose, one gallon honda anti-freeze, hand tools for removing exhaust mani if you choose to. (I did not)
A drill and 1/2" metal bit.
Heavy gauge aluminum sheet metal about 12" or less long and 6" wide.
A tool to cut the metal like shears.
You will need one of the following:
A tap for threading new threads into the plug. This tap must be the same threads and pitch as your nipple. I had one in the shop.
A small mig welder. This is what I did when my drilling abilities failed. More on this later.
You could have a local welder do this part of the job for you for very cheap, I am sure. If you choose this route, you also need a bench grinder.
Drain the cooling system.
Try to do this part of the work when the block is still warm to the touch. It wants to be cool enough that the exhaust won't burn you when you use leather gloves around it. Remove large bolt between cylinder 3 and 4. Use a 19mm socket and breaker bar or take of exhaust mani and hit it with a big hammer before attempting to losen.
Either drill and tap your plug or weld it. Either way, it has to be drilled with a 1/2" bit. A drill press would be best for this, but a decent drill and some patience will do. Try to keep the hole straight. Mine drifted enough to put an angle on the finished product. Not really that happy with that part of it.
I chose welding, it's faster, less likely to leak, and more permanent. These plugs are available from the dealer for about $12 but usually are not in stock. Plan ahead and order a spare if you are paranoid.
Finished product before paint (high temp). Note that I ground the nut faces of the original plug back down so I could tighten the plug again.
Thread this plug back into the block. You may want to shorten the nipple with an angle grinder and cut off disc so there is more clearance between it and the mani.
Mount your tank heater 1" or more below the level of the block plug. The bracket provided sucks, but it worked well enough for me. Plumbers tape would do the trick too. Run the hose to the inlet so there is very minimal kinking.
Cut the aluminum sheet metal long enough to get away from the mani. As seen in the last photo, the brown metal with clamps is my aluminum. I rounded the edges with the shears. I formed it with my hands and plyers. I put just enough tension on the clamps to snug the ends of the shield, not restrict flow.
Route the outlet hose to the outlet side of the heater core. I had to replace the other end of this hose as it was the only way to get the T in the correct direction. (see photo)
Clamp it all up, check all clearances, refill the cooling system and be very certain it is fully bled of all the air before plugging in the heater. I took it for a test drive after filling and idling until no bubbles were left. I then topped off the reservoir. When I got home the reservoir was empty and I topped off the radiator again. I'll check again after a long drive.
Yeah... I drive a civic around at 55 to get better gas mileage... Gotta be a guy with a sense of humor, right? ;o)
EDIT- and just so I'm not chatting... I am curious about the lower radiator drain plug as a legit location to instal the input for the heater. The heater instructions say it is, so I am just trying to imagine the flow of coolant to make sure it goes full circle.
Out drain plug > through block heater > Into heater core > back to engine > out upper radiator hose > into radiator > back to drain plug? Sounds right to me.
I've installed circulating engine heaters on other vehicles by simply splicing into the cabin heater rtn hose like this; cabin heater rtn to circ heater inlet, circ heater outlet to cabin heater rtn hose going back to engine. The warmed coolant circulates FIRST thru the engine block, then cabin heater & back to circ heater. Why wouldn't same work on a Honda 'D' engine? No need to get out wrenches, welder, machine tools, hammers etc. Eh.... might STILL need the hammers.