1999 Corvette radiator cooling fans do not come on even at 240 degrees engine oil temp. No modifications to cooling system; all of this is completely stock.

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The PCM will complete the ground path for low speed cooling fan relay under any of the following conditions:
• When engine coolant temperature exceeds 105°C (221°F).
• When A/C is requested and ambient temperature is above 9°C (48°F).
• When A/C refrigerant pressure is greater than 190 psi (2 volts).
• When the ignition is Off and engine coolant temperature is greater than 140°C (140°F).
The PCM will complete the ground paths for all engine three cooling fan relays under any of the following conditions:
• When engine coolant temperature exceeds 113°C (235°F).
• When A/C refrigerant pressure is greater than 275 psi (2.9 volts).

You still have many other components in that system that has to be in working order for the cooling fan to work properly. The cooling fan is turned on when engine temp reaches a predetermined temp, usually around 220-230 degrees F. the ECT (engine coolant temp) sensor siganls the ECM (Engine Control Module) to ground the cooling fan relay or cooling fan module(if equipped) and if the cooling fan fuse is good and the fan has power to it the realy will complete the ground for the fan to run. You may need to have a qualified technician diagnose the problem if the obvious things like fuses and good grounds are not the problem.

Hope this helps.

actually, the ECM directing the sensor to actuate the switches. the engine thermostat is the actuator of the fans in the cooling system. and its located in the oulet port of the engine where the upper radiator hose is connected. (and or at the lower rad hose, some design on VWs).

180--------have radiator tested soon along with the waterpump

Could be a faulty temperature sensor, at wost it's going to be a bad head gasket or intake manifold. Sorry for the bad news and hope that it's just a faulty temp sensor.

Thank you for using fixya and check your engine oil to make sure there is no coolant mixing in with your engine oil. Coolant is corrosive to your engine's internal bearings.

completely normal those readings are perfect this car comes with a 195 degree thermostat,210 is fine for stop a go traffic remember a cooling system with the proper amount of coolant in it and under pressure will not overheat till about 240 degrees your in great shape no conerns!!!!!...

250 TOO HOT FOR ENGINE AND TRANSMISSION. SOUND LIKE COOLING FAN CLUTCH BAD ITS FREEWHEELING NOT LOCKING UP TO DIRECT DRIVE TOO COOL ENGINE OFF BECAUSE THE FAN CLUTCH THERMOSTAT NOT WORKING THE HOT SILICONE OIL CAUSE IT TO EXPAND TO PUT RESISTANCE ON CLUTCH TO PUT DRAG ON FAN CLUTCH CAUSING IT TO LOCK IN GIVE IT DIRECT DRIVE.I WOULD STILL REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP IF TEMPERATURE STILL 250 DEGREES YOUR RADIATOR AND COOLANT SYSTEM NEED FLUSHING.

first i would purchase a new radiator cap 15 lbs 16 lb capacity cost about $7..then you must let car cool completely...now check radiator coolant level.. top off if it needs it. Now install new cap..let car warm up normally and after it get to normal temp range or higher put hand on upper radiator hose..it should feel hot and when you squeeze it you should feel a slight back pressure..this will mean that the thermostat and water pump are working correctly. if not either the thermostat you purchased is defective or your pump may not be working properly.
when you use just water in an engine the boiling point becomes 212 when you add the correct amount of antifreeze, depending on where you live, the boiling point will go up to 240 degrees. Make sure you put in the correct amount of mix.50/50 will usually work well. sometimes when a gauge does max out like that it could just be trapped air. if after you checked all this out and no air is trapped in the system, i would think that you may have a bad temp sensor. let me know if this helped thanks.

if this is an electric fan,first test your coolant temp sensor located in the block or possibly the radiator,then make sure theres not an obstruction in the system itself and have the system flushed out and the radiator boiled out(depending on radiator material)and checked,if its a newer model vette it may have a double-cross flow system and they plug up easier than the standard cross-flow system