OVER HEATING IN TRAFFIC

I gave my wife a 1990 Corvette convertible for a wedding present.  It has the L98 engine and recently received $1,454.30 in repairs at a local Chevrolet dealer due to blown gaskets (head gasket, manifold gasket etc. etc.)  mainly due to OVERHEATING in traffic (Dallas).  The dealer purportedly put a new thermostat in addition to replacing all the gaskets, changing the oil (I had coolant in the oil) and flushing and refilling the cooling system.  UNFORTUNATELY, the thing still overheats badly (240 degrees and up) in any traffic or slow driving.  I called the dealer, they said the fans don't come on until 237 degrees.   Any ideas??  Any suggestions??  Does this sound normal?  I had a 1996 Corvette coupe with the Grand Sport engine and a 6 speed manual that did the same exact thing - every time I got stuck in any kind of traffic snarl.  

does it blow the coolant out the radiator???    

if you are loosing coolant...  with the engine cold... take off the radiator cap.. examine it... is the brass disc in the middle of the rubber seal pulled up tight against the rubber??? or does it flop loose?????   if it is one of the flop loose versions... change it for one that is not...    16 PSI...

does the fan actually come on.. you can tell if the fan is being commanded on with a OBD1 scan tool....    they do come on as commanded by the ecm at 228 or higher...  237 is possible...  i just don't remember that number .. but it is floating in the back of my mind as being a number for corvettes..

how is your air dam and under bumper areas...    so any ram air will be forced through the radiator..  not leaked to the side...  is the a/c condenser filled with dirt and sand from dusty roads... blocking the cooling air..

is your cooling fan running at high speed/????   has anybody replaced it with an aftermarket unit...  not all are up to the full power specs.. once size fits all in the aftermarket...   no so with all of the gm or delco units...     i have also seen some aftermarket units missing the spacer between the drive flange and the front bearing... so when the fan is bolted on tight.. the drive plate comes loose... slips down the shaft.. rubs the motor case... and the shaft just spins as the drive plate is past the splines ...  

how slow is the idle speed?????    how many idle air counts are there at idle ??  20 to 50 would be in the normal range...  yes this is scan tool data..
if the engine is idling too slow.. slower than normal... there might not be enough coolant circulation to properly cool the motor...


on earlier models... the aux cooling fan switch is in the right cylinder head between spark plugs 6 and 8...   green wire...  so if the ecm fails to turn on the cooling fan... this switch will...  edit... just took a good look at the wiring diagram.. this system is totally controlled by the ecm...  

here is the wiring diagram for the 90 radiator fans

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/08/fd/ad/large/0900c1528008fdad.gif

this component locator will also help

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/08/fc/a5/large/0900c1528008fca5.gif