Overheats/ not the themostat

My 1997 Astro van would start to overheat and then settle out OK. This went on for months and then it quit settling out to the right temp. I replaced the thermostat and the situation remains. Any ideas out there?:banghead:

When does it overheat? While driving it? Or will it overheat just while sitting still and idling?

only two reasons for over heating. insuffcient coolant flow or insufficient airflow thru the radiator. when was the last time you flushed the radiator? the astros also have a habit of picking up leaves and other litter in the grill and shroud areas. clean all that out and pressure spray the outside of the radiator too to increase airflow.

Interesting piece here, recently my 97 experienced the same problem. I had the thermostat replaced and it would still overheat. Now it has been said, the coolant chevy used in these models was good for 150,000 miles. the problem being the crap turns to sludge causing havoc internally. A thorough flush more than once and sometimes more then twice is definitely needed. Look inside the radiator and notice the brown sludge in there. Flush the crap out of it and drain it. Since I've done this the heat has never been as hot as now.

Do you know the condition of your catalytic converter ?.Bad catalytic converter can cause some extreme overheating problem's !.

We went through the same thing with our 92, I flushed and cleaned and replaced the thermostat with no improvement. Turns out it was the fan clutch failing. I replaced it and all overheating went away. Hope this helps.