96 Deville running hot

We've had a 96 Deville since 97. It NEVER ran over 205 on a hot summer day even in heavy traffic. Last year it started running up to 225 in traffic but most of the time on the interstate from 203-210. I changed the thermostat and water pump with new GM parts. It still runs the same temp. Yesterday was 26 here and it still ran 212 driving 50 MPH on a snow packed road. The coolant level stays full. There is no leaks. the Cadi dealer I talked to thought it could be a radiator problem. When I replaced the water pump, the inside of the coolant system was very clean and the pump came out fine so that makes me think the rest of the coolant system is clean. I've heard people on here say not to worry about running that hot but if it didn't do that from 96-2003, something is not right with it. Any others ran into this problem?

It isn't a problem. The cooling fans don't even come on until 225. I can't account for the perceived variations, but the present situation is normal.

I agree! I don't think any overheating warnings come on until around 265 degrees or so! If it stays under 230 degrees most of the time, I wouldn't worry about it.

How do you explain the car running never over 205 even in the hot summer but these days can go close to 220 many times? Something has changed and I DO worry about it. The fans run when the AC is on but not until about 227 or so with it not on. Even with the fans running, it's still gets to the 212-217 mark at times. 212 yesterday when it was 19 outside.

How do you explain the car running never over 205 even in the hot summer but these days can go close to 220 many times? Something has changed and I DO worry about it. The fans run when the AC is on but not until about 227 or so with it not on. Even with the fans running, it's still gets to the 212-217 mark at times. 212 yesterday when it was 19 outside.


In the hot summer with the A/C on, both cooling fans will be running. The computer automatically calls for both cooling fans to run whenever the A/C compressor is engaged. In the winter, one fan is on only intermittently. Really, I would not worry about it, but if you feel that concerned about it, have the cooling system pressure checked to make sure it is ok.
I have a '94 Deville, and while it has a differerent engine, the 4.9, it gets anywhere from 199-215 degrees on the highway. And that is with a new radiator, replaced a month ago! The Northstar engines do run on the warm side, but like I said, it really isn't overheating until it gets to around 265 or so.

Even if it not overheating too much, it still runs hotter and more inconsistent temps than it used to all the time. Why?

Are you comparing the temps from last winter to this winter? Or just summer to winter? Has anything else changed with the engine, like weight of oil, thermostat, etc?

We've had a 96 Deville since 97. It NEVER ran over 205 on a hot summer day even in heavy traffic. Last year it started running up to 225 in traffic but most of the time on the interstate from 203-210. I changed the thermostat and water pump with new GM parts. It still runs the same temp. Yesterday was 26 here and it still ran 212 driving 50 MPH on a snow packed road. The coolant level stays full. There is no leaks. the Cadi dealer I talked to thought it could be a radiator problem. When I replaced the water pump, the inside of the coolant system was very clean and the pump came out fine so that makes me think the rest of the coolant system is clean. I've heard people on here say not to worry about running that hot but if it didn't do that from 96-2003, something is not right with it.

I'm comparing apples to apples. Even after I changed waterpump & thermostat, nothing changed. It used to never run over 205 even idling for a long time in 100 degree weather. I would even attempt that now.



Are you comparing the temps from last winter to this winter? Or just summer to winter? Has anything else changed with the engine, like weight of oil, thermostat, etc?

The only other thing I can suggest is that there is some scale buildup starting to form inside the radiator. And that is hindering it's cooling capabilities. How many miles are on the car now?

120,000 miles on the car now but when I read the temps in (178)and out(75) on the radiator the other day when it was cold out, it would seem like this is flowing ok and since the coolant going back in the engine was cool this is not causing the problem. What do you think? It read 201 at the thermostat housing but the instrument cluster in the dash read 212. Where is the sensor located? I will shoot it next.

The only other thing I can suggest is that there is some scale buildup starting to form inside the radiator. And that is hindering it's cooling capabilities. How many miles are on the car now?

It sounds like the radiator is doing a good job of dropping the temps. The temp sensor is on the rear of the engine, underneath the waterpump crossover. You can see it down there with a wiring harness attached to it.

120,000 miles on the car now but when I read the temps in (178)and out(75) on the radiator the other day when it was cold out, it would seem like this is flowing ok and since the coolant going back in the engine was cool this is not causing the problem. What do you think? It read 201 at the thermostat housing but the instrument cluster in the dash read 212. Where is the sensor located? I will shoot it next.
hi my friend,s 1998 deville has the same total symptoms you described in your car . did you eventually solve the overheating problem with your car? if so, please let us know . thanks for any advice.

I never did find out why it started getting hotter than before. I was going to change temp sensors but never did.

I Had This Problem With A 98 Deville. The Problem Was The Head Gaskets. I Didn't Believe It When The Dealer Told Me Because I Had No Leaks Or Coolent Lose. I Changed The Radiator, Waterpump And Hoses, Thermostat And Sensors. When The Car Ideled It Would Run 203 But If I Got On The Gas At Speed The Temp Would Climb Up Really Fast. Hope This Helps. I Have Had 3 Devilles, 2 96 's With The 4.6 And A 98 Concours With The 4.9. The Concours Must Have Been Beatin Somthin Furios Because It Sucks Gas And Repair Parts Faster Then I Can Make The Money. Good Luck