98 VOYAGER 3.0 V6 135K MI. COOLANT PROBLEM? on 1998 Plymouth Grand Voyager

i JUST BOUGHT IT WITH 135K MI. I DROVE IT 400 MI. AND ENGINE HAS A TAPPING NOISE AND THE TEMP GUAGE NEVER WENT ABOVE HALFWAY AND THEN DROPPED SLOWLY ALL THE WAY TO BACK TO THE C WHILE DRIVING GOING 60 MPH IN 20 DEGREE OUTSIDE WEATHER AND HEATER BLEW LUKE WARM AIR AFTER IT DROPPED DOWN TO THE C? OIL LEVEL AND COLOR IS FINE AND COOLANT OVERFLOW TANK IS ABOVE THE MIN MARK AND RADIATOR IS SHOWING FULL WITH NO BAD DISCOLORED REDIDUE(CHECKED WHEN COLD AFTER THE TRIP). NO MUD ON RADIATOR CAP. WHEN I WAS INITIATALLY CHECKING VEHICHLE TO BUY I DID NOTICE SOME WHITE FILM ON INSIDE OF ENGINE OIL FILLER CAP. SALESMAN SAID ALL OF THOSE 3.0'S HAVE THAT AND THAT ITS JUST TRAPPED MOISTURE WHICH I SAID THAT LOOKS LIKE THERE IS A COOLING SYSTEM PROBLEM OR BAD HEAD GASKET. I ALSO NOTICED A COOLANT SMELL INSIDE THE VEHICHLE AND DID SEE A STAIN ON PASSENGER SIDE CARPET (DRY THO).

by in Lyle, WA on December 31, 2010
2 answers 1 comment
ANSWER by on December 31, 2010
Sounds like your thermostat is not working properly, thus the cooler than normal running temp and low heater output. The stain on the carpet may be dried coolant. ( leaking heater core? I hope not for your sake )The moisture on the oil cap may be normal, as long as the oil color is clear and not milky and the coolant looks green and not milky.
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COMMENT by on December 31, 2010
Thanks. I will go ahead and change my thermostat and boil both the new and old thermostats to check and compare. even new ones fail from time to time. appreciate your response.
ANSWER by on December 31, 2010
Your coolant problem is a leaking heater core.