My 1996 corvette lt1 will overheat while standing,fan does not come on,i have to put on a/c and both fans come on and car cools down to normal.i checked fusesand replaced,thermostat cooling sensor,temt switch,3 fan relays at left side of radiator is it posible the water pump is going

SOURCE: electric cooling fans

Agreed. Change the coolant temperature sensor. Make sure NOT to use teflon tape on the switch. This will not allow the switch to ground and the switch will never be read correctly by the computer.

SOURCE: Cooling fan wont work

The water temp sensor is located near the thermostat housing. This sensor is what tells the ECM to turn the fan on/off. The water temp sending unit is located near the same area. You know you have the correct sensor is because the water temp sensor has a 2 prong plug. The water temp sending unit only has 1 prong.

SOURCE: car overheats. have replaced radiator,thermostat.water

Question that I pose is:
Is the car overheating or are you assuming it is as the gauge is telling you that it is?
There are two cheap and simple things that are not mentioned in this post. There is an Engine coolant temp sensor which in all of their innane wisdom Saturn built with a plastic tip and we all know plastic melts fairly easily. This part is a simple fix as it needs a 13mm deep socket and that is it for tools to replace it and it is $10 - $15 for a new on with a copper tip. There is also an Engine coolant temp switch which sends information to the PCM to tell the gauge what the reading should be. Aslo $10 - $15 and a 13MM deep socket to replace. These are common issues with the S Series Saturns. I do however recomend that if you are going to replace them yourself that you empty the radiator of coolant as the sensor and switch are directly in the engine block coolant flow and will give you a nice little shower if you do not at least jack the drivers side up before replacing them.

SOURCE: cooling fans not working on 1995 camaro z28

you have a burnt fan relay...if it were my car i ould run a jumper to the fuse panel so that when you turn the key on the fan will also come on and run.its not hard to do and it will stop the car from overheating

SOURCE: high mileage 1996 Ford Explorer v8 overheats at 75-80 mph

if your mechanic seen no leaks from hoses or thermostat housing its sounds that either your fan clutch or your thermostat is bad. if its heats will driving streets and not highway its your fan clutch and needs to be replaced. if it overheats in streets and highway its your thermostat and needs to be replaced,you will need a thermostat and gasket with some silicone. Drain, follow the radiator hose to the housing and take 3 bolt off, clean housing well,CAREFULLY install the t-stat exactly the way is was taken out (pic), gasket,sillicone, bolt.    its an easy job. Good luck!