Cadillac: 1999 Cadillac cooling system overheating, temp variance, heat range

Question
Tom! I have a Sedan Deville 4.6 Northstar.  Recently I had the thermostat change due to high temp reading (222-230) and the situation got worse.  Now the temp runs 230-260 and shuts off.  I have had the radiator checked, flow blockage checked, engine pressure checked, gasket pressure checked, I have replaced the coolant twice.  I still get the same problem.  In addition My check engine light came on and the codes says I need an EGR valve.  Before I replace the water pump are there any other thing that could be wrong (Temp Sensor).  My fans come on at 230 degrees. Any suggestion I am going batty.

Answer
There is NOTHING wrong with a temp variance of 222-230 as this is within specs.

I would re-install the old thermostat or replace it with the EXACT same style and heat range as the old one.

Your still within OK specifications. normal engine temp during normal driving is 220 to 230 with the cooling fans coming on at approx 230. In traffic driving or long up hill climbing can raise slightly.

Are you POSITIVE you installed the EXACT same heat range thermostat and style that you removed.

You CANNOT replace the thermostat with a lower temp setting as it screws up the cooling and driveability sensors of the vehicle.



NOTE: the coolant mixture is critical and make sure that you have ALL the air out of the system.