Originally Posted by PatrickGSR94

First drain the coolant from the radiator thru the drain plug, then disconnect the lower radiator hose from the radiator to let coolant drain out of there. Put the radiator hose back on.

Next locate the coolant drain bolt on the engine block. On B and D series engines it's behind the exhaust manifold/header, slighly towards the tranny end of the block. It's a BIG bolt, 19mm I believe, hard to miss. Remove that. Have a large container ready, because it will come GUSHING out. After it finishes draining, replace the bolt.

Now comes the tricky part. Remove the lower radiator hose and coolant temp sensor from the thermostat housing and then remove the housing w/ the thermostat. One of the housing bolts is pretty difficult to get to, so have some wrenches or a swivel socket joint handy (I can't remember what I used). Put the housing back in w/o the thermostat and reconnect the lower hose.

Now remove the upper radiator hose from the radiator and point it towards your drain bucket. Stick the garden hose into the top of the radiator where the upper hose connects and run the water. The remaining coolant in the block will be flushed out through the upper radiator hose. Keep the water running until the fluid coming out of the upper hose is clear. Remove the block drain bolt again to drain the remaining water from the engine block.

Reinstall the thermostat and coolant temp sensor and all hoses etc. Fill the radiator w/ a 50/50 mixture of coolant and water (Honda pre-mixed, or Prestone and distilled water, do NOT use Xerex or Peak as it contains silicates which can damage the radiator). You will have to pour it in SLOWLY as it tends to bubble up and spurt out of the filler hole while you pour it in (I found a special radiator funnel at AutoZone which fits the radiator opening perfectly, but I still recommend pouring very slowly and putting paper towels around the filler neck).

Once the coolant reaches the base of the filler neck, locate the bleed bolt where the upper radiator hose attaches to the cylinder head. Loosen this bolt and let the coolant flow out until it flows out steady w/o bubbles. Squeeze the upper radiator hose to help get any remaining air out of the system. Continue squeezing the upper hose until no more bubbles come up at the base of the filler neck, and continue to add coolant as necessary to keep the level at the base of the filler neck.

Now start and run the engine with the heater slider set to HOT. Continue to run the engine until it fully warms up and the radiator fan comes on. The lower radiator hose will also become hot (the upper hose should already be hot). After this the coolant level in the radiator should have dropped since the thermostat opens and allows coolant into the block and the heater core. Shut off the engine, and continue to fill the radiator until it get to the base of the filler neck.

Added 26 March 2004: After filling the radiator and first starting the engine, while the engine warms up I notice the fluid level in the radiator tends to rise (expansion I guess before the thermostat opens). Most sources I've seen say to run the engine either w/o the radiator cap (Haynes) or with the cap on only to the first click (Helms). In either case, coolant comes out of the filler neck and makes a big mess all over the place, so last week I just put the radiator cap on fully while the engine was warming up to prevent a mess.

Remove and wash out the coolant overflow tank, fill it to the proper level with the same 50/50 mix, and you're done!