COBALT TEMP GAUGE READS 250 DEGREES BUT ENGINE RUNNING COOL REPLACED COOLANT TEMP SENSOR AND STILL GAUGE GOES TO 250 DEG

Well then the engine isn't hot enough ! The engine computer will turn on the fans when the coolant temp sensor tells the PCM/ECM the temp is 212 degrees . Does the temp go into the red ? If no don't try an read problems in that aren't there .

If you replaced the SENSOR and not the gauge SENDER, there's your answer.

The SENSOR sends the computer (ECM, PCM, ECU, etc.) the engine temp so it can make the adjustments to the fuel, timing etc.

The gauge SENDER makes the gauge read what temperature the engine coolant is.

Hope the helps.

ok , but no engine stated. which one>??
hot = lying dash gauge or real hand held pyro IR gun? a $20 tool.
did the scan tool ECT reading show too hot, Yes/no.

no new cap, really?
is the cam timed right?
is the spark timed right.?
is the ECU stuck in limphome mode? (huge heat to cylinder walls)
thermostat not upside down.
or thermostat not with bleed hole up hill trapping air below
making it lie and the dash gauge lie too, (the gauge can not measure air, period)

id not do squat with no IR gun. not me. its super accurate too.
and dirt cheap and saves burned hands,
and finds clogged rad tubes saving useless $250 new rad.
one tool. use it. and win.


i this this dang I6 engine, that loves to trap air?
had 3,now, over 500k miles on them. 1988 to present.
and never overheated but once, pin hole in heater core hose
ran bypass and drove home.
i have a 08 wrangler 6sp, 3.8L v6 , nice rig. easy to fix too.

there are 2 parts. (3 really)
engine make too much heat, (limphome or timed wrong)
air in system.
cooling system.

the rad pressure test pass and the green/blue test passes

no water in engine oil
no oil or carbon seen in the engine coolant , all places look.

how hot, ??????
200f
260F
280F"?
numbers matter, in all ofscience. they talk to you.
at what exact temp did the fans, kick in,?
the FSM shows you this, and how to do that. how to make sure the
fans kick in happen, RIGHT. some are 2 staged with A/C.
not just kick. (when)

was the thermostat installed the correct way round . Fans should start spinning at around 75degres c. Check coolant temperature sensor ( not temp. gauge sender unit) for operation. Have a flow test done on the radiator to check for blocked cores.. Have a compression test done to check gasket and for cracks.

This sounds like a bad coolant temp sensor that give computer false reading, check the coolant temp sensor connector and if it is good with no bad wires to connector then replace coolant temp sensor , when the computer gets a signal from temp sensor that engine is hot it turns fans on high speed to cool radiator and displays a/c turned off , if this truck does not have electric cooling fans then they wont run just explaining what happens depending on engine and cooling set up. replace coolant temp sensor and check connector.

Using your tatco code reader, select current data (real-time data) and select engine coolant temp sensor (ECT). Run engine to operating temperature (A/C off). Monitor the temp reading - when the temp reaches approx 204 deg farenheit, the fans should kick on, after the temp drops to approx 198 deg farenheit, the fans should turn off. The fans are controled by the ECM (Engine Control Module). The ECM controls the cooling fan relays.

250 DEGREES ENGINE GETTING TOO HOT.SOUND LIKE CLUTCH FAN FREEWHEEL.IF CLUTCH FAN DONT LOCK IN OR HAVE RESISTANCE TURNING BY HAND WHEN ENGINE HOT.FAN CLUTCH IS BAD.IF FAN CLUTCH OKAY COOLANT LEVEL CORRECT.I WOULD CHANGE THERMOSTAT FLUSH OUT ENGINE AND RADIATOR.IF ENGINE TEMPERATURE STILL READS 250 DEGREES OVER FLOW JUG OR RESERVOIR NOT BOILING OVER THE COOLANT TEMPERATURE SENSOR FAULTY.

I had this problem with a 2007 Chevy Cobalt. I changed the coolant sensor and even though the check engine light went out I still had a reading of "---" on the coolant gauge. The problem is most likely one of three things: a low coolant level, a bad coolant sensor, or the thermostat needs to be replaced. The only other possible thing it could be is a bad BCM (Body Control Module) which in that case you would most likely be having other weird problems.

The Thermostat and the sensor are both very easy to get to and replace. Take off the engine cover by removing the oil cap and they are both to the rear of the engine on the driver's side. They are right next to each other.

Hope this helps!

Do you have a digital gauge that reads in numbers or a needle that goes from blue to red? Coolant will boil in a pressurized unit at 265 degrees F. plus, But you don't want to come anywhere near this temp. It should run at about 185- 200 F. Maybe more. So keep it cool. Hope this helps.

if i disconect temp sensor fans come on cool engine but then no temp gauge

That's what I'd expect after unplugging.
This is sounding like a bad coolant temp sensor. Test it or replace it before you do anything else. Read this post on how to test an engine coolant temperature sensor

Test engine coolant temperature sensor Ricks Free Auto Repair Advice