Chrysler Repair: 96 Chysler New Yorker overheating, oil filler cap, head gasket leak

Question
I've had intermittent problems with my '96 New Yorker overheating.  Changed the thermostat 2 months ago and it began overheating again today.  I cannot find any leaking hoses or leaks around thermostat housing or from water pump, and the radiator fan seems to come on and run normally.  I removed the air filter this evening thinking maybe some blockage there, put water only in the fill tank and ran it this evening, it overheated after about 20 minutes with fluid gushing out of overflow.  I heard some intermittent puffing sounds just before overheating (could this be from air filter being off)  Any ideas on where to look for the source of this problem.  

Answer
Hi John,
Two possibilities come to mind, the first is rather conventional, the second more significant:
1. The flow thru the radiator is impeded by buildup of deposits in the tubing. It would be worth doing a radiator flush to try and improve the circulation. By the way a 50/50 mix of coolant is a better agent for exchanging heat than water.
2. If the temp gauge didn't seem to be moving rapidly toward the top, just on H side of middle, and yet it overflowed from the expansion bottle with  puffing sounds but no major clouds of steam, I would suspect that you have a head gasket leak on one of the cylinder banks. If you have been loosing fluid with no noticeable loss to the ground or overflow bottle, and if you have noticed (or will now look for) excessive white smoke that has an odor of antifreeze in the exhaust gas when you start the car after it has cooled down (let the smoke condense on you hand then smell it) and/or milky-cloudly oil on the dipstick or on the underside of the oil filler cap, then those are the signs of a break in the gasket which separates the compression chambers-oil passageways-water passageways from one another. It also will cause over-pressurization of the cooling system and drive water from the overflow bottle even though the water is not superheated and steaming when it comes out. So if that seems to some of the symptoms that you are having you would want to remove the spark plugs after the engine cools and see if any of them appear to be wet, and then have a helper crank the engine to see if water squirts out of any of the spark plug holes just when the cranking begins as a sign of such a head gasket leak and if so which bank of cylinders needs to be attended to with a new gasket. Any of those symptoms, or if you want to detect it scientifically, a measurement for exhaust gas in the cooling system by a radiator shop, will confirm this is the problem. Otherwise, then try to clean out the radiator.
Let me know about any of these symptoms/possibilities and maybe I can give you some more direction. But puffing/gushing without a lot of steam would be suspicious of a headgasket leak.
Roland