GM-GMC: rattle/grinding sound and coolant smell, cooling system pressure tester, coolant loss

Question
I have a 2000 S-10, 4.3L with 211,000 miles. Very recently, I started hearing an intermittent rattling/grinding sound when either driving or just idling, and with it seems to be the smell of coolant (a little in the cab, stronger outside). To a certain degree you can even feel the vibration, and it seems to have gotten worse over just a day or two.

Anyhow, given the coolant smell and the puddle under the engine, I checked the weep hole on the water pump and noticed that there was quite a bit of wetness under the hole and below the pump. Considering the high-mileage, I figured that the water pump was just dying a painful death, so I replaced it. Great, found the problem, right?

Unfortunately, I started it back up and found the problem had not changed. Still rattles/grinds intermittently and coolant smell is still there. Haven't seen any new puddle yet, but I only ran it for maybe 5-10 minutes before shutting it back down.

Some observations that may or may not have any meaning here:

   * been getting a cylinder #4 misfire code off and on for about 6 months.
   * see no sign of oil in the coolant.
   * haven't really noticed any significant coolant loss.
   * haven't seen any smoke to speak of from the tailpipe.
   * rattle/grind seems worst when driving, but still intermittent and does happen while idling too.

Thanks in advance for any and all advice.

Answer
It is entirely possible that you have more than one concern here, the water pump was leaking and that was remedied.  If you are certain that you have no coolant entering your oil than the symptoms you presented point towards a heater core leak.  They usually start small and the smell is the coolant evaporating before any runs out the drain.  What you can do is get a cooling system pressure tester and apply 15 -18lbs of pressure.  I can help locate the source of small leaks.  As for the grinding sound, a quick check you can do is to remove the serpentine belt and run the engine (for a short time) and see if the grinding noise is still present.  If it is, it could be an internal issue, if it does disappear, start spinning all the accesories by hand and see if you can determine which pulley is grinding.  And on a side note, pull the spark plug on cylinder #4 and see what is going on there.  Look for signs of burning coolant etc.  Replace it with a new plug and exchange the wire for that cylinder with another one the same length to see if the misfire moves.
Hope this helps