my firebird does the same kind of thing , except that even with my fan i put in with a manual switch it still overheats.... only in traffic or hot days...expressway is fine...i used to drive 5 miles to work , and by the time i got there parked and got out , my overflow tank would be boiling over and steam coming from under the hood. I checked the anti freeze mixture , if it was flowing which it was , and i do have to shroud on along with the air deflector underneath. this thing has me stumped. it pins the needle at stoplights , and a half mile down the road its at normal , and boiling when i park it. what can you tell me about that?

 

so you are sure the fan is coming on. then i would check to make sure the thermostat is working. you will be able to touch the radiator hose and tell if water is flowing through it. then i would make sure none of the hoses are binding or collapsing. also make sure the rad cap is good. or you may have a pocket of air in the system, try burping it. make sure water pump is good. also check the main engine coolant - oil. might also want to check for obstructions to the radiator or mashed fins which will restrict air flow. sounds to me like either the fan isnt working or there may be a coolant flow restriction. check and see what temp the fan is switching on at.

 

awell the first thing i noticed is the original fan would only work sometimes.... so i went and bought a new electric one , used the original shroud and put the new fan in hooked up to a toggle switch , so at first i let it idle in my driveway..so i could check to see if the coolant was flowing through the radiator , and it was , so i took it for a ride and the same thing...pin the needle at red lights , and cool down a half mile down the road..its almost like the fan only slows it down , but it will still get to boiling in the overflow when i park it. , there are only a few fins on the radiator that are no good , looks like they just got pushed on from putting the new fan in or something , nothing bad at all. the cap on the other hand , i dont know to much about that , and i could just go buy a new one , they are cheap. also when it come to burping it , isnt that when you just take the cap off and let the car idle and wait for all the air to come out of the system?thanks for all your help and info , i appreciate it.

 

with your aftermarket fan i take it you have it wired so you can turn it on manually. just make sure the fan is working properly and in the correct direction. there are puller and pusher fans. if the upper hose gets really hot then there is coolant flowing through it and the thermostat is opening. next check the lower hose for softness, it may be collapsing and blocking flow to the engine. to burp the system remove the rad cap and let the enging run with heater on full for a while while keeping coolant level full.
usually when the car overheats mainly when stopped is because the rad fan is not functioning properly. but check these things and let me know what you find out.