98 deville 32 valve North Star OVERHEATS after 33 miles of drive ?? does not overheat in town overheats out on highway and after slowing down- fans dont cool motor unless stop engine ,have changed radiator and thermostat, cooling fans do NOT operate after engine turned off w/ ignition key OFF and have high temp - 244 degrees

check the tension of the fan belt. also make sure there is no debris on the radiator.

For car running hot and overheating issues, I suggest to you go through this help links.

Click this link below and go through the troubleshooting procedure to take care of the problems: ----

Car runs hot?

http://howtobyme.blogspot.com/2011/11/car-runs-hot-in-traffic.html
-----------

All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html
---------

Car freeze overnight and started overheating while driving?

http://technoanswers.blogspot.com/2012/01/car-freeze-overnight-and-started.html

-----------

Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

---------------------------

Car overheats and Air blows hot at idle?
http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
--------

overheating?

http://schematicsdiagram.blogspot.com/2011/12/buick-century-overheating.html
----------

Car engine Overheats and transmission starts slipping?

http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html
----------This details will help.Thanks.

No, you can't add too much coolant. Rather, it does not hurt anything if you do. Did you add it to the radiator, or to the overflow tank?

Let it cool, then remove the radiator cap, and if needed, add coolant to the radiator. Put the cap back on, and fill the overflow tank to the "full - cold" line. Start it and run it a few minutes and look for leaks. If you find no leaks, drive it for a day or two, then let it cool and check it again. If it is down a lot (without overheating), you have a leak somewhere. If you lose enough coolant, that will make it overheat. However, if it overheats, that can cause loss of coolant, when you stop the car, you will see steam and smell coolant, and often hear it boiling.

If it overheats again, make note of when it happens: driving on the highway, or stop-and-go around town. Overheating on the highway usually indicates a clogged radiator, while in-town overheating usually indicates a bad cooling fan (you don't need the fan above about 30 MPH). A bad fan is usually the fan relay, but it can be the fan thermostat (different from the engine thermostat), or a bad fan motor.

Two things you can check: First pull your oil dipstick and make sure that the oil is clear and not cloudy or milky, if it is you have a blown head gasket. Secondly if the vehicle has an electric fan make sure that it is coming on. You can do this by starting up the vehicle and letting it warm up for 10min or so or until the guage shows that it is hot. Then look under the hood to see if the fan is turning, you may have to watch it for a few min because they will cycle on and off. If the fan doesn't come on, that is why it overheats in town because it is not getting enough airflow across the radiator. If the fan does not come on you can start troubleshooting it by checking the fuses and relays in the dash and under the hood. If the relays and fuses are good and the fan still won't come on, with the key on and engine off, carefully wiggle the wire that goes into the fan, these sometimes make bad connections, but again be careful because if that is the issue the fan will begin spinning so watch your hands and fingers.

A clamp might not be needed, this is not under pressure. It would not hurt to have one, but a simple spring clamp is adequate.
A vehicle can overheat for many reasons. When does it overheat most? During periods of slow speed, stop-and-go, and idling? Or during long high-speed drives on the highway?

If it is mostly idle and slow speed, check your cooling fan. Mostly they are thermostatically controlled, only turning on when needed. If this does not work, check the fan relay, fan motor, and fan thermostat.

If it overheats mostly at high speed, it is most likely that the radiator is partially plugged and needs to be backflushed, rodded, or replaced.

If it always overheats quickly after startup (less than fifteen minutes) it may be that your thermostat is not opening properly.

You need to get the cooling fan checked,it may need a temperature sensor,fan relay or the fan motor may be burnt out.You can check the fan by running your own power and ground to the plug that comes out of the fan motor,unplug it and put the ground to the black wire and positive power to the other one,if it works then the next step would be to check the fan relay.The most common problem if the fan doesn't work but can be made to work with jumper wires is the temperature sensor,you can check it by unplugging it and jumping the wires in the plug.If the rad fans work then you are down to either the water pump or a plugged radiator,a rad shop should be able to narrow it down for you.

i would get a radiator tester to make sure there is no air leaking out at a slow rate

When driving down highway only, it overheats? When running steady, I take it you mean, sitting idling? If it's only overheating at highway speeds, and all else has been checked out & is o.k., I'd take a close look at rad hoses for soft spots (easy to squeeze) that may be causing hoses to collapse at highway speeds & restricting flow of cooling system. Another thing to try is, turn your heater on high fan & high temperature when it starts to heat up & see if temperature gauge goes down (cooler) at all. If it does, then rad not doing it's job properly.

is the a/c running or not??
if it is check to be sure the auxiliary fan comes on when you turn the a/c on!!!
if thats ok then it's probably your fan clutch!!!

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!