Changed water pump on my 98 deville but it stills overheat

Run the car without the thermostad to see if it still overheats. If so check the heat sensor it might be faulty.

First, you must have a properly installed thermostat that is working correctly. Second, Northstar engines are notorious for air in the cooling system after draining and refilling - keep checking the purge tank level after overheating and after the cooling system cools down. Third, make sure your cooling fans are working correctly (relay, fuse, temperature sensor) - check to make sure both are running when it overheats. If all the above is correct, the problem will probably be blockage in the system (try a flush) or your water pump itself is failing.

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
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All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html
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Car freeze overnight and started overheating while driving?

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

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Engine Overheats and heater blowing cold?

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

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

http://schematicsdiagram.blogspot.com/2011/12/buick-century-overheating.html
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Car engine Overheats and transmission starts slipping?

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

check belt tension for the water pump if belt too loose pump will not send enough water in and will cause your engine to overheat, also check that your coolin fan is working,

Whatever you do, NEVER allow this engine to overheat and always use the correct antifreeze (DEX COOL) or you will damage your heads severly. The heads were made from aluminum so there is a very serious warping issue on the 1998 Cadillac Northstar engines. There should have been a recall but wasnt, ended up costing me 3 thousand USD to fix the engine problems I had but she now runs fine. I only had the car 4 months before this happened so someone prior to me owning evidentaly let it overheat on too many occassions and I had no choice but to fix cause I was still paying on the car!! Good luck

if the car overheats all the time, idle and driving, then check the water pump

if the car only overheats at idle, check the cooling fan

flush your radiator first.with the thermostat out you should see the water moving if not bad water pump.this engine needs the thermostat to function properly and either a 50/50 coolant or straight coolant so it does not boil over.also make sure your fans are coming on

The oil life resets to zero after the engine overheats. Check for external leaks first, make sure the water pump belt is still there and turning. The most likely cause if the car has over 70,000 miles is head gaskets.

You likely don't want to hear this but Northstar engine a common for head gasket failures. One good test that I use it to fill the coolant tank all the way to the top. Then start it up. If the coolant shoots out of the tank. The heads have a problem.

check to see if there is a valve (usually vacuum actuated) inline somewhere on the lines that go from the block to the heater core. Maybe it is stuck...