[BigLee]

CRUISE-CRUZE, thanks for sharing
this cooler Dorman thermostat.
I have a 13 Sonic, and I have modified a couple of conventional thermostats to fit into the 1.4T housing.
I use a resistor to satisfy the PCMs
Looking for voltage/no voltage on the heater circuit.
This dorman is a much better option though.
It also offers potential to have a driver selectable dual temperature capability.
I wired up a switch to the thermostat heater circuit to manually control it while driving. Once the engine stabilizes at ~178°F, I can turn on the heater circuit, and on the highway, the engine temp will drop as low as 156°F at 85° ambient temp. Takes about 40-60 seconds to drop that much.
This could be good for things such as track outings, ect.
And contrary to popular belief, I believe that cooler operating temps could actually be beneficial to fuel economy.
I think that at lower engine temps, detonation is less common, so more timing advance can be used.

My normal operating temps now run between 173-178°F.
If this seems to be a bit lower than typical, it could be because when I was swapping out the "guts", I noticed that the original spring was about 1/8 inch shorter, and seemed to take a bit less pressure to compress, so I kept the original spring.
Now wether this spring is deliberately calibrated differently, just a manufacturing variance, or has softened a bit from use, I dont know.

 

[BigLee]

I forgot to mention that with the other thermostat I fabricated, i was running around 190°F, and my fuel economy is up from this time last year running the stock 217° thermostat, from about 37 to about 42 mpg.
A good portion of this increase is likely due to improved driving techniques, but I think part of it may be due to the cooler operating temps.

 

[BigLee]

If anybody is concerned that the Dorman thermostat is of lower quality, I am also fairly sure that both the stock GM/ACDelco and this Dorman thermostat are made by the same company/plant.
They both say
"made in Czech Republic" on the packaging, have similar numbers and scan codes etched onto the wax pellet body, and where the the GM part# sticker is on the side of the housing, you can see where this sticker has been peeled off of the Dorman, as evidenced by residual adhesive.

 

[BigLee]

Interesting.
Did you buy the Dorman 902-2080?
I just installed a second one in my wife's 2017 Trax tonight, and both of them are identical in construction to the originals.
I have seen the ones that have a different design to the machanical parts, so I presume those are the ones you are talking about.
Apparently those are made by
Motorad???

 

[BigLee]

902-808 is the correct one for stock replacement.
But we are talking about using the Dorman 902-2080, which is intended for the Volt/ELR, and swapping its internals into the original housing, to make a cooler operating thermostat for the turbo engines.
Now the OEM opening temperature for the Volt/ELR is the same as the Sonic/Cruze/Trax LUV 1.4, at 217°F.
Somehow, this 902-2080 is opening at 175-185°...
I can only presume that this thermostat was originally intended for for a market where emissions regulations are not as strict.

 

[BigLee]

Just did a road trip with my wife's Trax with the new thermostat.
Ran between 170-180°F the whole time

 

[BigLee]

I'm able to get them, but I didnt bother looking at them beforehand.
I'll look to see what they are currently at tomorrow.
Fuel economy has been great though.
Just over 34 mpg (DIC) fully loaded, and with A/C running the whole time over 400 miles.
Mix of interstate, state highway, back country roads, and some in-town driving.

 

[BigLee]

Ok just got home and fuel economy on the DIC indicates 34.6 mpg.
The long term fuel trims on the trip home floated around from -3.5% to
+3.5% most of the time, often under +/-1%.
On rare occasions, I would see momentary spikes to a little over +/-5%.
It seemed to spend a little more time in the negative territory than positive overall.

 

[BigLee]

What a great thread, my 2013 40K miles has always smelled of antifreeze after I drive it--especially in the summer, I garage it and the smell is horrific in the garage every time I use it, I believe the odor is the water outlet which distorts just enough to allow some venting, although there is no leakage with the dealers static pressure test and hardly noticeable coolant loss I believe the temperature is too hot for the plastic parts long term, I'm sure the GM engineers have figured out why all the coolant related failures happen but are stuck in a rock and a hard place in that they have to satisfy the emissions with the high temps but experience high failure rates of the cooling systems, hey its all good for car sales with the reduced life on the engine from the heat----I'll be doing this mod soon !!!

I agree.
I think that the plastic cooling system components are very close to their limits of durability, especially longterm.
My 13 Sonic has had 4 water pumps (not plastic, but the seals are definitely stressed), 2 resivoirs, a water outlet, and a radiator replaced.
I think that lowering both the temperature and pressure will greatly reduce the stress on these parts.
Lower pressure surge tank caps are available, and are definitely recommended as well.
GM/ACDelco part#s are:
15 psi - 15075117 / RC98
9 psi. - 88986846 / RC108
The 9 psi cap is probably best used after the cooler thermostat, and an auxiliary radiator fan switch is installed.

 

[BigLee]

Agreed if you are still using a stock thermostat that 9 psi is a bit low.
But with the cooler thermostat and an auxiliary fan switch, 9 psi is quite acceptable.
True, it does give you less margin if the engine does run hot, but if you monitor your temperature, you should be able to spot a problem well before things get too hot.
Then again, it may also help prevent a component failure that could result in coolant loss, and subsequent overheating...

 

[BigLee]

I think the fuel trims look pretty normal.
They will typically fluctuate a bit like that.
As for that thermostat you posted, you know that isnt a direct replacement, right?
You would have to modify it heavily to try getting to fit a stock housing.
Also, since these are inlet side thermostats, you will have around a 5-15°F temperature rise at the water oulet.
So a thermostat that starts to open at 187° on the inlet side will result in about 197° outlet temperatures, +/-5° depending on engine load.

 

[BigLee]

There isnt a "fan sensor" or fan switch.
There are coolant temperature sensors which report to the PCM.
The PCM tnen decides when to activate the fan.
The PCM uses these coolant temp sensors for all of its coolant temperature related decisions, so replacing them with ones of a different value would wreak havoc on many different operating calculations.
The add-on fan switch is an easy way to sense radiator temperature and trigger the low speed fan relay well before the PCM would.
I havent studied the Cruze cooling fan circuit, but on the Sonic And Trax, there is a place you can tap into one of the factory fan relays to trigger low fan speed without the PCM being aware of it.
If the Cruze uses 5 relays to control the fan, then it is likely this can work for them as well.

And pressure is as big, or even bigger factor on the durability of the above mentioned cooling system parts than just temperature alone.
Both my Sonic and my wife's Trax now have the cooler thermostat, the added fan switch, and the 9 psi caps.

 

[BigLee]

I never claimed it ran different.
Just that there is less stress on above mentioned parts, and their lifespan will likely be much longer.
I am aware that the boil over threshold is lower, but I monitor temps closely and wont let it get too hot.
And like I also said, both our vehicles now run considerably cooler than stock...

 

[BigLee]

Agreed.
The lower temps play a major role.
The plastics are physically stronger at the lower temps.
But pressure is also important.
I've seen several sudden failures of surge tanks rupturing, even radiator header tanks suddenly give way, leading to total loss of system pressurization, rapid coolant loss, and naturally immediate overheating that leads to a tow bill.
When you see how thin some of these plastic parts are, it's a wonder they last as long as they do.
Pressure is no less than half the culprit...
If you arent comfortable with 9 psi, at least consider 15 psi...

 

[BigLee]

Engine temperature wont significantly affect NOx.
Maybe if its overheating it might affect it more.
NOx forms when combustion temps exceed around 2500°F.
They used to control this with EGR.
The exhaust gas was mixed into the intake charge to act as a buffer gas, preventing peak combustion temps from crossing over 2500°.
Nowadays, they simply allow it to form during combustion, and use improved catalytic converters to break it back down.
The higher engine temps are meant to help reduce hydrocarbon emissions. The difference is small though. But with the EPA counting every molecule coming out of the tailpipe, it sometimes helps tip the scales into a more favorable emissions tier category, which gets additional credits to the manufacturer...

 

[BigLee]

And some of the problems persist to this day, sometimes despite 2 or 3 supposed design revisions to address known issues...

This engine was an Opel design to begin with, so it was in use in Europe for 3-4 years before being offered in the U.S. market.
It had sufficient time to get the bugs ironed out.
I dont know what temps or pressures these early European market vehicles used though.
Perhaps GM upped them on the U.S. models.

 

[BigLee]

Just look at my original post and see the picture with the initial coolant reservoir. High temperature & high pressure are not for this vehicle! The 15psi cap works the best, going to 9psi may risk to boil the coolant if the mixture is not properly done.
And I said before, GM moved back to a lower temperature thermostat lately. Look for example the 2018 Cruze, it has the thermostat that starts opening at 180F! In theory, yes, higher temp and pressure will give you better performances. IF.. you use quality components, but if you try to cut cost everywhere, using cheap materials, then have the decency and change also the mechanical components to adjust to the new situation. View attachment 283383

I agree.
Maybe I'm a little overly cautious with using the 9 psi cap, but thus far, it's working well on both vehicles, and I am confident that cracked plastic cooling system parts are a thing of the past.
I work at a GM dealership, and I see first hand the number of failed cooling system parts being replaced on Sonic, Cruze, Trax and Encores. It's rare that a day goes by without one of these vehicles being in our shop for a coolant leak somewhere...
Mixtures are good...
And I've had a long history with running cooling system pressures between 7-10 psi on lots of vehicles in the past. No issues from it.

 

[BigLee]

Just an update.
My Sonic has been using the Dorman 176° thermostat for over a month now, and our Trax has had it for over 2 weeks, and both passed OBD inspection today.
The spring issue I mentioned above doesnt seem to have made a difference after all, as both vehicles seem to have pretty much the same operating temps on the highway.
Both cars are daily driven, and
no codes have appeared on either vehicle.

 

[BigLee]

I assume you are talking about going to closed loop.
And 133-135°F used to be the minimum temp before closed loop was permitted on older GM models, but these cars are capable of going to closed loop operation at much lower temps.
I've seen my Sonic go to closed loop after a cold start at ~45°F ambient at ~65°F coolant temperature in as little as around 40 seconds after starting.

But if you are talking about the readiness monitors, they are already set from previous drives, regardless of current coolant temps.

 

[BigLee]

Installing a colder thermostat might set a DTC for thermostat performance sooner or later. The ECU monitors operation of the thermostat by comparing engine and radiator Temperature and maybe also ambient temperature and expects specific values after a certain engine run time. If they`re not met, it will set a code and MIL after a few drive cycles
You can alter the desired ECT by changing it in the calibration

@BigLee:
the engine does have internal exhaust gas recirculation.. this is realized by the VVT system, not by an external EGR valve.. in medium load conditions, specific timing of the exhaust cam makes the exhaust valves stay open for some time of the intake cycle… this allows some exhaust gases to be sucked back from the exhaust manifold into the combustion chamber and being burned again. In this engine this is enough to reach the desired emissions

Well, my car has been through a few hundred drive cycles with the cooler thermostat, and so far no codes.
Not saying it wont ever set a code for low temp. Fall and winter are approaching, and we'll see how things go then at ~176°
It went through last winter at ~190° without issues.

And VVT isnt there to provide EGR.
The valve timing alterations needed to attain sufficient exhaust gas dilution would almost certainly be detrimental to both fuel economy and driveability. While it's true that you almost always have some residual exhaust gas in the cylinder from the previous firing, it's not enough to to prevent NOx formation threshold.
The formation of NOx is actually an indication of a more fuel efficient combustion event, as it provides more heat (and thus pressure) to drive the piston with.
The converters break down the resulting NOx...