1985 Chevrolet Silverado • 140,000 miles

After about a 30 minute drive, highway speeds (55-60) once the truck is in park, a strong "heat" smell is present, and you can hear the coolant boiling in the lines. I'm fairly sure that a small boil over occurs, probably no more than 8 fluid ounces hit the ground. This is a recent purchase, but most of the coolant seems to be thin, and more watery in texture than coolant.
February 15, 2013.

Replace the coolant and then bleed the cooling system-start here if it continues have it pressure tested

Feb 15, 2013.
Awesome, thanks for the response. Follow up question if you don't mind. This vehicle was purchased as a second mode of transportation for the time being, and would probably do no more than 10-15 miles every other day, if not less. Obviously I want to fix this issue, the follow up question would be: if I don't (can't afford to either time, or money wise) have that checked/done right away. Do I run some risk of serious damage to the vehicle? The route traveled would be on speed limit streets of no more than 45MPH if that matters any. I appreciate any and all help with this.

Feb 17, 2013.