Overheating Light: At what temp turns it on?

[LorbeerTLC]

Hey gang, got a question for those who are mechanics and to those who actually know the answer to this question:

"What is the minimum temperature the coolant has to reach before the Temperature Warning Light is activated?"

Please, no guesses or "guesstimates." I'd like someone who's actually seen the specifications on the OEM coolant temperature sensor and has either seen it in writing or have had one activate while they had a coolant temperature gauge (and it wasn't malfunctioning).

Reason: I have gauges in my car and would like to know what the minimum coolant temperature needs to be to activate this light. I also know that a 50/50 mix will keep the Sonic from boiling up to about 265F. But does that mean it's ok to drive it at such a high temperature?

I also know the OEM thermostat is 221F (105C) and even though it's electronic or "MAP," knowing this information in advance would be nice to have. I've asked a couple of GM mechanics and their resources do not list the answer. They honestly don't know!

Thanks!

 

[Maddmatts]

The manual describes the thermostat operation as beginning to open at 105C (221F) and fully open at 120C (248F). Chevrolet Sonic Repair Manual: Cooling System Description and Operation

As you can see there's no description of what is considered overheated.

However there is an OBDII DTC for overheating (P0217?), it might be possible for someone with tuning software to look the code up and see what the trigger condition is.

 

[LorbeerTLC]

Fully Opened at 248F (120C)?!!

Am I the only one or does anyone else think, "THAT'S INSANE!!"

Can this engine handle temperatures up to the boiling point of 265F (129.5C) without damage? opcorn:

 

[LorbeerTLC]

Behold: Chevy Cruze in Canada!

Well, upon further investigation... I know that the Chevy Cruze uses the same engine that's offered in the Sonic (1.4L Turbo). So I went and looked-up a picture of the Canadian Sonic's dash...

The picture shows the temperature gauge red-lines at just above 125C (257F). So I'm guessing the red bar above it is probably around 129.5C(?) or about 265F. Since the boiling point when mixed 50/50 and with a 20 pound pressure cap is at 265F, I'm going to say that's probably when the light comes on. Dang, that's really hot! I now know that if my gauge gets to 260F, it is considered too hot and to take immediate action (ie: turn on heater to HIGH!). I hope it never gets that hot, but at least I now have a benchmark to go by.

 

[skurtov]

Well, what you might consider hot really isn't.

Firstly, these cars are designed to run on the hotter side of things. Its to squeeze out the better MPGs. Thats why stock opening temps are at 220.

Second, you have to remember that a coolant system runs under pressure. As pressure in the system increases it keeps the coolant in its liquid phase. Reading from the this Valvoline sheet, a 50/50 mix at 15psi starts boiling off at 265 degrees F. However, this was done at a fixed test facility, if I was to surmise, pressure would build over the 15psi as the coolant starts to heat up in our car. Might afford a few extra degrees of liquid state before boiling. Which is nice.

Thirdly, the real question is if the block can handle going that high. Which due to how small and thin the cylinder walls are. I would doubt they could last long without warping

So it's reasonable to say that the high coolant temperature light should ignite anywhere from 240 to 245 allowing enough time for the car to be shut off.

Also, the Sonic's do have temperature readouts, UltraGauge or my personal favorite and OBD2 and Torque app work really well.

https://sharena21.springcm.com/Publ...2d889bd3/5a76d5fc-0cbd-e711-9c12-ac162d889bd1

 

[LorbeerTLC]

So it's reasonable to say that the high coolant temperature light should ignite anywhere from 240 to 245 allowing enough time for the car to be shut off.
https://sharena21.springcm.com/Publ...2d889bd3/5a76d5fc-0cbd-e711-9c12-ac162d889bd1

Probably higher. The tech manual say's that the thermostat starts to open at 221F (105C), and be completely open at 248F (120C)[without assistance]. And since the Canadian Cruze temperature gauge redlines above 257F (125C), I'm guessing the light will probably come on at around 260F.

I'm also thinking temperatures that high have got to put stress on the plastic inlet and outlet housings that are bolted to the engine head.

 

[JTee2017]

Yes. .. these operating temps seem a bit on the high side to me also.

And I think it does have a part in the early demise of the T-stathousing, 1.4L "water outlet" and more.

There was one member here in a thread I read awhile ago who removed the factory T-stat form it internal mount and cemented in a 195F thermostat in it's place. That seems like a more reasonable operating temperature. But not sure if it would cause other issues.

 

[LorbeerTLC]

There was one member here in a thread I read awhile ago who removed the factory T-stat form it internal mount and cemented in a 195F thermostat in it's place. That seems like a more reasonable operating temperature. But not sure if it would cause other issues.

Wow! I wish I could talk to that guy. I was thinking of doing the same thing however, this is one of those "Next Generation" electronic or MAP thermostats that are controlled by both coolant temperature and/or an electrical signal from the ECM. If the engine is operating under a heavy load before the coolant has warmed up sufficiently, the ECM will send a signal to fully open the thermostat. (In theory) This is suppose to prevent certain components from getting too stressed prematurely while still maintaining high temperatures for fuel efficiency and low emissions. Unfortunately, I've heard some people are having issues with coolant leaking from the plastic outlet housings and I can't help wonder if it's due to the high operating temperatures.

Because of this, I decided against doing anything that might mess with the ECM unit. But if this guy was successful in not throwing any engine codes (like, engine too cold), I might reconsider it!

 

[skurtov]

The thermostats are electronically controlled on our cars. One of the things that the BNR tune does is change the opening temp down to your 190 degree range.

 

[Gimpster]

After my experiences on my car, I think the higher temps don't help things. That said, like I just ranted in the general area, there are a lot of failure modes/vectors on the cooling system of these engines in general. It's cheap where it shouldn't be and over complex, a bad combination!

I wish the aftermarket would produce more stuff to address this, ie: cast coolant necks, thermostat housings etc vs. intakes and stuff that doesn't really do anything for the car.

 

[Stew]

Well the highest value for ECT is see in HPTuners is 248* but that's for fan speed control. I don't see anything for an overheat light on setting.

Same in the DTC section, just checkboxes for enabling trouble codes, no values for when they're triggered.

 

[Gimpster]

I would guess the BCM handles the dash idiot lights.