AC Off Mode: Bad T-Stat?

[John_C]

Was on my way home 5am when all the sudden my car goes in to AC Off mode because of supposed over heating.

Temp gauge in the dash was cold. Digital readout was ---F.

Turn the car off and tried to turn it back on to see of it goes away and it won't start.

I then checked my coolant system... No leaks that I can see. The radiator was full. Top hose was hot. Radiator was cool to the touch. Low radiator hose was cool. T-stat housing was hot. Heater hose was hot. Heater worked.

I always bring a OBD2 scanner and/or my HP Tuners and Laptop.

So plugged in the HP Tuners OBD2 and got on HPT and cleared the code and then it fired right up.

For maybe a half mile from the gas station to home was 198F via HP Tuners log.

Checked radiator and lower radiator hose and they were still cool, yet everything else was hot.

So do I have a bad t-stat or is it an air pocket in the cooling system?

If it is a air pocket, am I lifting the head?

I did get in to boost o the way home part throttle......

[olblue75]

I agree T Stat their cheap enough to replace.

[xc_SS/RS]

More than likely it’s a stuck tstat. I’d check the wiring of the coolant sensor as well (drivers side head I think)

Should still give a readout even if the tstat is stuck

['10CamaroDude]

When mine overheated (serpentine belt broke), I got a warning, not a dashed readout.
It still didn't shut the car down on me, I did it myself and coasted into a convenience
store where I waited from 2AM to 6:30AM for a "AAA" tow. A dash'd readout should
be an indicator the ECT sensor went.

[InFiD3ViL]

Not sure how a bad stat would cause a dash readout like that though, but who knows. I would be eyeing that coolant temp sensor. But then how does HP Tuners pull the coolant temps without an issue, as it should be getting the same info as the dash/ECM?

But your lower hoses being cool points to the stat or air pocket.

Sorry man, just thinking out loud. These cars are so weird sometimes.

[fif_gen_powa]

Friend had same issue, I would think it would be coolant temp sensor rather than tstat. It happened randomly to him a couple times and after battery reset would go away. He disabled the code with hp tuners and that was that

[StingrayblueSS]

Originally Posted by John_C

Was on my way home 5am when all the sudden my car goes in to AC Off mode because of supposed over heating.

Temp gauge in the dash was cold. Digital readout was ---F.

Turn the car off and tried to turn it back on to see of it goes away and it won't start.

I then checked my coolant system... No leaks that I can see. The radiator was full. Top hose was hot. Radiator was cool to the touch. Low radiator hose was cool. T-stat housing was hot. Heater hose was hot. Heater worked.

I always bring a OBD2 scanner and/or my HP Tuners and Laptop.

So plugged in the HP Tuners OBD2 and got on HPT and cleared the code and then it fired right up.

For maybe a half mile from the gas station to home was 198F via HP Tuners log.

Checked radiator and lower radiator hose and they were still cool, yet everything else was hot.

So do I have a bad t-stat or is it an air pocket in the cooling system?

If it is a air pocket, am I lifting the head?

I did get in to boost o the way home part throttle......

This happened to me last fall. In cooler weather it would take to long to get up to operating temperature and it would say a/c off due to high engine temperature. Changed the thermostat and it was fine.

['10CamaroDude]

Oh, wait a minute, I just remembered. When my HHR overheated due to running
over a recap from a truck tire; once it went passed 264 degrees, it turned into
dashes! Yeah, I forgot about that! I saw it hit 264, then three dashes. That
means it REALLY overheated. I got lucky, there was no damage to the engine.

It was 13 degrees out, and I was stranded 100+ miles from home. So, I would
stop, sit for 5 minutes, start and run it to 70, turn it off and coast. I had to
do that repeatedly till I got to the Walmart. They were closed (Xmas day), and it was
FREEZING, so I forced the doors open, sorry, no way a tow truck would be
there in time before I froze to death sitting in the car. There were people in
the store though, they just asked how I got in. I said, the door just opened.
That was the truth, they didn't ask how, AND they were stuck open...

YES, I see a lot of carnage, driving 1400-1600 miles a week.

[John_C]

So basically I'll try a t-stat and a coolant temp sensor first.

That said.... This is a really weird issue. If I had to guess, I'd say stuck thermostat judging by how hot everything else was versus the radiator and lower radiator coolant hose.

Btw... Which was does the coolant flow?

Does the hot fluid go in from the driver side top hose and cooled fluid go out the passengers side bottom hose to t-stat housing?

[StingrayblueSS]

Originally Posted by John_C

So basically I'll try a t-stat and a coolant temp sensor first.

That said.... This is a really weird issue. If I had to guess, I'd say stuck thermostat judging by how hot everything else was versus the radiator and lower radiator coolant hose.

Btw... Which was does the coolant flow?

Does the hot fluid go in from the driver side top hose and cooled fluid go out the passengers side bottom hose to t-stat housing?

Maybe check your thermostat in a pan of water on the stove. Pretty sure the upper hose is the return to the radiator

[John_C]

So I ran it hard....

Got to the work parking lot with the hood up and the car started getting hotter.

It climbed real quick once it got to about 2/3 and hit 248F before I shut it off.

Fans kept running a while.

['10CamaroDude]

Originally Posted by John_C

Btw... Which was does the coolant flow?

Does the hot fluid go in from the driver side top hose and cooled fluid go out the passengers side bottom hose to t-stat housing?

From the upper radiator hose, down, and is pulled into the motor from the
lower radiator hose. That's why some cars have a coil inside the lower
hose, so it does not collapse. When hoses get aged, they soften, and get
flexible. So, some cars have the hard coil inside the hose so that won't
happen.

[Greenhornet2]

Tstat is very easy to change. You can even take it out and test it to see if it opens by boiling some water or pushing ut open by hand. If the coolant is full and you've got no leaks a cold upper hose tells me either the tstat is stuck, or possibly your water pump is not circulating. It could also be air but in this situation it seems pretty unlikely.

[John_C]

Wasn't sure if it was lifting the heads or not, so went ahead and pulled them today.

Checked everything out and no blown head gasket. No coolant in oil. Coolant looked like new.

We did find the thermostat was stuck and the last person who worked on it left the plugs on the back of the heads loose, so they were leaking coolant from there.

So went ahead and installed LSA / LS9 MLS head gaskets, Cometic MLS exhaust gaskets and ARP head studs.

Topped it off with new fresh coolant and a oil change.

Now on to the trans.... It has a hesitant hard 2nd to 3rd shift

It's a fresh built Tim King 6L90, Circle D triple disc 3400 stall, and DSS 1 piece aluminum DS.

Going to do a new TEHCM and Sonnax Zip Kit rebuild on the valve body Doing another full synthetic trans fluid change, filter and new pan gasket as well.