i have an 87 2.5 auto fiero with 110,000 miles on & a new water pump last march 2000. didnt drive much in winter. this spring temp would rise then fall constantly. I removed the thermostat so coolant would move freely. nothing changed still happens. temp light comes on now, i dont know what is wrong. there is plenty of coolant in the system. Are the coolant lines clogged? is radiator cap bad? please email me if you can help. thanks

Try a new thermostat, I did the exact same thing, new stat last year and now the darn thing won't work right!
New one worked and fixed the problem.