My Cadillac Deville, 2002 northstar is running hot........or the temp gage goes up and I have to stop driving..I have a new thermostat,relay switches for the fans,temp control sensor and a new coolant reservoir.......Is there a machine that can tell me exactly what this is.....Is it electrical, coolant still in resevoir....thanks, Bill

thermostat change and radiator cap choose the right one

You have a Blown Head Gasket.. It is a 4.6 Northstar Engine. Very Common around 90-105K

As you can see, a couple of fan relays. Use a jumper wire on load side of fan relay, the load side is the line with arrowhead. The red wire going to load side of relay, top wire in diagram is hot all the time. As far as the control side of relay, the voltage is fuse protected and goes hot with key on. I couldn't get everything in diagram, the coolant temp sensor is involved. Any applicable trouble codes?

replace the blower motor

Are you sure the thermostat was in the wrong way ?.

The thermostat is located in the bottom hose unlike most conventional cooling systems.

The thermostat in the Northstar engine is a dual action device.
One end of the stem is the Thermostat(obviously) and at the other end is a spring loaded pressure valve(the thinner end).

Make sure the thermostat end is nearest the rubber hose and the pressure valve end is in towards the engine.

Also note that the cooling fans don't come on until the coolant temperature hits around 225 degrees.
During normal highway driving the fans will very rarely come on(if at all) due to constant air flow through the radiator.They will only usually come on in heavy traffic conditions on a hot day.
But......if you have the Air Con switched on, the fans will run all of the time.

For overheating problems consider the following......

The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.

Your electric fan is probibly not running.Fan switch,fan relay or the fan could be bad.If it is getting hot and you pop the hood you should hear the fan running.

The thermostat in the northstar engine is located at the bottom radiator hose (unlike most conventional cooling systems), the hose connects into the housing where you will also find the water pump.

You will need to remove the air filter housing and air duct to gain easy access to the thermostat.

Remove the hose from the housing,then remove the two bolts on the flange,the thermostat can then be pulled out.

Take note of the orientation of the thermostat as you remove it.

The thermostat in the Northstar engine is a duel action device.
One end of the stem is the Thermostat(obviously) and at the other end is a spring loaded pressure valve(the thinner end).
Make sure the thermostat end is nearest the rubber hose and the pressure valve end is in towards the engine.

Don't forget the new gasket when you install your new stat, you may have to order this separately.


Overheating........

The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.

Also note that the cooling fans don't come on until the coolant temperature hits around 225 degrees.
During normal highway driving the fans will very rarely come on(if at all) due to constant air flow through the radiator.They will only usually come on in heavy traffic conditions on a hot day.
But......if you have the Air Con switched on, the fans will run all of the time.

4.6 Northstar V8. It is located on the rear of engine (driver side) in front. It is 1n the the waterpump housing cover. Remove airbox and intake tube and bottom radiator hose. 2 bolts(believe 10mm) on thermo housing. These systems are a lil finiky about air pockets....so fill slowly and let run at idle until operating temp and let cool and chk level.....fill as needed and repeat if needed.

Sounds like you need a new Temperture Control Sensor. Also these engines are prone to leaky Head Gaskets so be aware.

the first thing to check is to have the engine running. as soon as it reaches operating temp the upper radiator hose should get hot. if it doesn't then it's the thermostat. if it does then i believe your water pump is probably not circulating like it should and it should be replaced. however before replacing the wter pump make sure that the wire to sending unit is tight and not giving you a false reading. if your model has electric fans make sure the fans are running when the engine is hot. if they are not running check the relay in the fuse box for the fans with the engine running switch out the fan relay with the a/c clutch relay. ifthe fans kick on replay the relay with a new one. if they don't click on the it's either a bad wire or the temp sensor probe is bad. hope this answers your question. please rate this solution...thanks.