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Electronic control of thermostat temperature 1.4T

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#1 · (Edited)
Happy New Year!

This is a variation on the original mechanical solution thread which is found at-
www.cruzetalk.com

1.4 ECO - Thermostat Swap - 221°F to 176°F!

OK, let’s start! I had multiple Cruze cars since 2011, unfortunately I can’t say I have/had one free of issues! Talking about the heating and cooling, I saw different & multiple issues reported by people. I did many changes to my cars during the years and I’m going to share with you a few...
www.cruzetalk.com www.cruzetalk.com
Thanks very much to the OP for a great thread!!!

---------------------------------
NEW-
There is now a group of "how-to" writeups located at-
www.cruzetalk.com

HOW TO- Electrical control of the 1.4T (LUJ) thermostat...

Per @Blasirl here are a group of tutorial writeups and links to 3D printed part file sources. They describe methods and options for electronically controlling the thermostat temperature on 1.4T (LUJ) engines, and defeating the active "Aero" grille shutters. The effect of these modifications is...
www.cruzetalk.com www.cruzetalk.com
---------------------------------

I replaced my '12's thermostat last year because the gasket was leaking rather badly and the housing appeared to be weeping through the plastic (as revealed using UV dye in the coolant).
For that reason I did not save the OEM housing and the new one is aftermarket (and not Dorman) so I cannot easily try the mechanical core replacement as shown in the original thread.
Besides, 180F was a little low for me and I wanted something closer to 195-200F as others have expressed.

My unmodified thermostat ran at about 222-225F when cruising around normally, and reached 230F under load conditions.
This is completely insane as far as I am concerned and required attention.

Being an engineer I got to thinking, if the thermostat is electrically controlled (or at least "modified") by the ECU, why not just electrically adjust the operating temperature?
According to my FSM, page 9-596 (see below), at 0V to the internal heating element the opening temperature is 221F (105C).
And at 12V applied to the element the opening temperature is 176F (80C).
Notice that the fully open temperature is stated to be a staggering 248F (120C)...gasp!
Image


The element has an electrical resistance of about 16.2 ohms, or at least mine does.
So at 12 volts it will dissipate about 8.9 watts.
My target of around 200F is roughly halfway between the FSM's stated 0 and 12 volt temperature values.
But I suspected it is non-linear for the applied voltage, being instead proportional to the power being dissipated.
My target was therefore about 4.5 watts.
For a 16.2 ohm heater element that would be at approximately 8.5 volts applied.
So I needed to drop ~3.5 volts from the switched battery voltage rail that is available on pin 1 of the E41 connector to the thermostat housing (page 9-40 of the FSM, shown below).
Image

At 12 volts that would require a series resistor from the bottom end of the heater to ground of about 6.65 ohms.
Image

Such a resistor would dissipate around 1.8 watts, but being in the hot engine bay it needs to be de-rated to at least double that.
I happened to have a 6.3 ohm 10 watt resistor on hand, so that was what I used.
You could use a common "anti-hyperflash" load resistor as found for LED turn signal applications.
They tend to be right at 6 ohms in resistance and 25-50 watts in capacity (overkill but so what?).

Next there was the problem of satisfying the ECU which monitors things such as this for being disconnected.
I happened to have (literally) about a thousand 2.2K ohm 1/4 watt resistors laying around, so I connected six of them in parallel to get a net resistance of around 367 ohms, replacing the thermostat heater across the E41 connector in the connections shown above.
This will keep the ECU happy so it doesn't set any fault codes and even when the ECU switches the output on fully it will only dissipate 0.4 watts (but again it must be derated for being in the engine bay).
This is my test circuit-
Image

I used a 3/8" ring terminal to obtain a good engine ground from the bolt that holds an external cam sensor in place.

The switched + is available on pin 1 of the E41 connector-
Image


So now the problem became how to make proper and safe electrical connections.
I do not generally like to modify the factory wiring, though you could splice into the wiring if you wish.
You cannot easily or cheaply find a replacement for the harness connector, and cannot find an equivalent of the thermostat housing end at all.
But as it turns out the connector pins are about 0.108" in width (2,8mm) which fits with the "2.8 DCS" designation shown in the FSM (see above).
So male and female terminals such as are used on the narrow pins of car speakers will work nicely (0.110" tab terminals and female disconnects).
You can find them on eBay and elsewhere pretty easily.
22-24 gauge wire is more than adequate for connections because the currents are small.

A note of caution-
When wiring the female tabs for the thermostat housing, use heat shrink tubing over them so that they cannot short together.
If they do short to each other you will either overheat the 6 ohm drop resistor, or blow the KR75 fuse, or both.
And be certain to use dielectric grease (silicone grease, or plumber's grease) on all the connections to exclude moisture because the original weather seals will not longer be present (note the goo in the connector as shown below).

This is what my setup looks like-
Image


Image

I 3D-printed a fancy holder for the two male tabs to the E41 connector, but it is not necessary.

---------------------------------------------------------------
Long story short (I know, too late...), it works..!
---------------------------------------------------------------

Now it runs at 194-198F at low cruising loads and at about 201-204F on the highway or when climbing hills.
So far, after dozens of warm up cycles and restarts, no DTCs, no issues of any kind, and no apparent hit to gas mileage that I have seen so far (or too small to notice).

Because the electrical system voltage at E41-1 is not really 12 volts (it varies), that may account for some of the variations I am seeing in temperature.
Next I am going to try using a regulated voltage to the thermostat heater instead.
This will have the advantage of being easily adjustable and will have a schematic like this-
Image


The regulator I will try is a commonly available LM2596HV 3 ampere regulator module like this-
Image


These are not expensive, and you can find even cheaper ones (but be careful of the input and output capacitors, the ones as shown above are the better ones)-
www.ebay.com

LM2596HVS LM2596HV DC-DC Adjustable Step Down Buck Converter Power Supply Module | eBay

Specification: It's LM2596HVS Not LM2596S Chip,please know it Type / name:LM2596HVS DC-DC step-down module Input Voltage:4.5V ~ 53V Output Voltage:3V ~ 40V Output Current:3A (max) Conversion efficiency:92% (the highest) Output Ripple:<30mV Switching frequency:150KHz Operating Temperature:-45 ℃ ~...
www.ebay.com

Anyway, I wanted to offer this alternative method of controlling the engine thermostat temperature that takes advantage of the built-in electrical heating element.
I know that it is not for everyone, but if you are a bit electrically inclined it is a non-invasive and easy to install and de-install method.
And it definitely works...
 

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#34 ·
First I thank you for all your effort to solve the obvious defect the cruze has, and I do not either think a .61A load is much, I was most concerned with durability due to the fact it is most likely a Chinese made part with questionable durability, my experience with stuff like the heater winding and cheep parts is they will use the smallest possible wire size to save money, but I see yours has stood to continuous use so I'm going to have to try the mod--thanks again, I know how much time goes into studying and engineering a fix for stuff like this--great job !!
 
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#35 ·
You are most welcome.

Per discussions in another similar forum thread, I often wonder how many other problems have been caused by this "design feature" (225F-235F operation).
Horrid coolant smells, chronic reservoir tank overflow issues, accelerated deterioration of underhood components such as connectors, wiring loom and hoses, and shortened head gasket life are just a few possible things that come to mind.

As for Chinese-made parts, I am not defending them but the OEM unit was almost certainly made there.
As is the replacement part I have on the car now (Cardone-branded as I recall).
For all I know it may have been made in the very same factory, or maybe not.
I have no way of knowing but the replacement sure looked identical to the OEM part.
So far so good.

I replaced it a couple of years ago while chasing coolant leak smells and its housing lit up bright green from the UV tracer dye I put into the system.
It might have just been the molded gasket weeping and some surface seepage but I thought it would be better to premptively replace the whole thing.
Perhaps running at 225F-235F all the time was the root cause of that failure too.
I don't know and will likely never know for certain.
FWIW... :)
 
K
#36 ·
My 2013 with 48k miles smells of antifreeze every time I use it, took it to the dealer when under the B-B warranty complaining of it at 20k mi, they supposedly pressure tested it saying no leak found, the service writer tells me then its not leaking badly enough yet and GM will not replace the water outlet, my theory is the excessive heat warps the part slowly, the odor is always there and I've caught it dripping off the outlet when hot, very frustrating the way GM has handled these known problems !
 
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#37 ·
Oh my...
My sympathies to you.
That is the subject of a whole bunch of forum threads here.
Search for "coolant smells" and it will pop up like a bad rash.

I added a drain tube to the overflow outlet on the reservoir tank that goes all the way to the back of the car.
It is made from vinyl air tubing and is silicone RTV-sealed in place at the coolant tank so that any leakage and smell is transferred far rearward.
Eventually I ended up replacing the tank with the Dorman unit (recommended by others on the forum) and reinstalled the drain tube to it as well.
The Dorman tank has metal reinforcements at the hose attachment points because they tend to crack or collapse on the OEM version.

I also replaced the water outlet manifold some time ago because it was weeping through (!) the plastic body itself.
Apparently the plastic used for it can be somewhat porous and I suspect that the excessive heat did not do it any favors.
Later on I fabricated an aluminum top hose fitting for the manifold using double o-ring seals because even the replacement leaked where the overflow hose attached to it.
There is a Dorman part for that top outlet fitting that is reportedly much-improved.
I only found out about its existence after I had fabricated my own fitting, but I had fun making it anyway. :)

BTW, after making those changes, changing the thermostat housing, changing the water pump (another heat casualty, I am totally convinced), and lowering the engine's operating temperature to around 200F, there are almost no coolant smells anymore.
Some minor ones at times, but not even remotely close to as bad as it was before.

FWIW...
 
T
#38 ·
With the 180 tstat on my dil's 14, there are no more issues. Hasn't lost any coolant in 12000 miles. No smells, no leaks. Car runs great.
Yes, she drives that Cruze all over the place.

Reducing operating temps and repairing the pcv system properly should be labeled 1 and 1a of "things to do when buying a gen1 1.4t Cruze"

Sent from my SM-G986U using Tapatalk
 
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#39 · (Edited)
thebac said:
With the 180 tstat on my dil's 14, there are no more issues. Hasn't lost any coolant in 12000 miles. No smells, no leaks. Car runs great.
Yes, she drives that Cruze all over the place.

Reducing operating temps and repairing the pcv system properly should be labeled 1 and 1a of "things to do when buying a gen1 1.4t Cruze"

Sent from my SM-G986U using Tapatalk
Click to expand...
(y)(y)
Amen to that.
Mine no longer loses coolant either, even running at ~200F.
And an added plus is that it idles and runs smoother.
So far at least, the pcv system on mine is still OK, but I'm sure it will need repaired one day...

Slight update (18AUG2022)-
Still working perfectly!
I am no longer paranoid about the operating temperature, although I do check it from time to time.
No coolant loss, little or no coolant smells, no DTCs, and it definitely seems more "peppy" due to the lower operating temperature.
It just works. :)
 
D
#41 · (Edited)
Hi,
I haven't ever made any kits for sale, unfortunately, just the plans.
The regulated version is the one that remains on our car and it is still working perfectly by the way.
Now there is only the occasional minor random coolant smell but absolutely nothing like it used to be.
But don't forget that I also have replaced other "problem" parts such as the water outlet manifold, the bleed hose fitting to it, the thermostat and housing, the water pump and the coolant reservoir.
The non-regulated version will work well enough and would be relatively simple (and inexpensive) to make.
Let me think about it.

On a trip back east recently I drove past the former Lordstown Assembly plant (now Foxconn).
So sad...
 
D
#43 · (Edited)
OK, I will see if I can source the parts at a reasonable price nowadays.
The connector to the thermostat housing is a purchased item that I can't do much about cost-wise.
The connector to the wiring harness is something that I 3D printed.
The rest of the parts including the regulator board are commercially available parts for the most part.
They don't take long to actually assemble.
The regulated version is indeed better if only because it is adjustable so that you can obtain whatever target temperature range you want.
But as mentioned in my posts and writeups, the temperature will vary slightly depending upon driving conditions.
I'll get back to you soon.

Update-
I haven't forgotten, I am still gathering component prices.
I built mine almost entirely from things I had laying around collecting dust, so my own build costs were minimal.
As a result I suspect that you may not like what I would have to ask you for them.
You'd be much better off buying the parts and either building them yourself or finding an electronics hobbyist locally to build them for you.
I will be happy to provide you a detailed list of the items, sources and their current costs if that's what you would like to do.
I could make you the 3D printed connectors for a very low cost though, as they might be the most difficult thing to source.

Further Update-
OK, I have sourced all the parts for three versions.
With only a modest charge for my time in constructing and testing them they would be as follows-
Simple version (resistor limited, no plastic enclosure) $46 each
Regulated version (with plastic enclosure) $62 each
Regulated version with voltage display (inside enclosure) $65 each
Shipping and any local sales taxes not included.
The commercial parts such as the thermostat housing connector, enclosure (as applicable), power resistors, wires, wire loom and so forth, comprise the lion's share of the price.
But I am really not in the business of building and selling such things.
I have no problem if someone else on the forum would like to do so.

The nice thing about this method is that is non-invasive and can be removed within a few minutes if you need to do so.
And on the regulated versions you can easily tune the temperature to be what you want it to be.
Just remember that the operating temperature will still vary a little depending upon the operating and weather conditions because it is a fixed bias being applied to the thermostat.

FWIW (30DEC2022)-
My modification is still working perfectly.
190-195F operation typically, few if any coolant smells any more, no codes, no issues, and the engine just generally seems happy. :)
If you build and try it, I think you will be pleased.
If you want to try it on the cheap (push-in connections, short wires, 6 ohm LED "tail light" resistors, and no enclosures) you should be able to do it for well under $15.
And if you don't like it, you don't even have to touch coolant to remove it.
 
D
#44 ·
Well, I see that someone has duplicated my circuit and now offers it for sale on eBay.
www.ebay.pl

Thermostat control module - lower coolant temp. Astra, Insignia Cruze 1.4Turbo | eBay

Thermostat control module - lower coolant temp. Astra, Insignia Cruze 1.4Turbo | Motoryzacja: Części, Części samochodowe i akcesoria, Chłodzenia silnika | eBay!
www.ebay.pl
It doesn't bother me because I did not create it to make money personally.
However it is rather gratifying to see that someone else has independently validated the method and even made a video about it..!

Interesting that it is about $56 USD for the adjustable version shown.
So that also validates the price I estimated.
I would encourage anyone who wants to try this method of engine temperature control to just buy it from the eBay listing.

By the way, mine is still working perfectly and I have no intention to remove it, ever.
Very few if any coolant smells now, and the heater still gets toasty warm this time of year.
It works exactly as intended.
:)
 
A
#45 · (Edited)
There is also second version with built-in display.
www.ebay.com

Thermostat control Module- lower coolant temperature Astra J Insignia Cruze 1.4T | eBay

Find many great new & used options and get the best deals for Thermostat control Module- lower coolant temperature Astra J Insignia Cruze 1.4T at the best online prices at eBay! Free shipping for many products!
www.ebay.com
And version without display below:
www.ebay.pl

Thermostat control Module - lower coolant temperature Opel / Chevrolet 1.4Turbo | eBay

Thermostat control Module - lower coolant temperature Opel / Chevrolet 1.4Turbo | Motoryzacja: Części, Części samochodowe i akcesoria, Chłodzenia silnika | eBay!
www.ebay.pl
 
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#48 ·
Sure.

1) if ECU control is OFF, the relay is OFF and does nothing. The thermostat is taking power from the DC-DC buck converter, 10V or whatever you set.
2) if ECU control is ON, the relay is ON and bypasses the DC-DC buck converter, giving full 12-14V to the thermostat and it opens normal. This is the case if the temperature goes too high.

I've just replaced the resistor in the original schematic(in this thread) with the coil of the relay(wich has about 70 ohm in my case). So when the coil is energized(if the coolant temperature is too high, as without this module), it bypasses our module and works as the original GM wanted.

Note: the DC-DC converter has common GND(IN-OUT) and just V+ is controlled.
 
C
#51 · (Edited)
1. All we need is the ability to feed the t-stat heat element 1214v when we need to override the ECU.

2. The ECU needs to be fooled into thinking it's still connected to (at least?) a 15 Ohm resistance.

3. When we back off (0 Volt to the heater) the ECU must be taken off the dummy 15 ohm resistor to be re-connected with the real one (inside the thermostat) to avoid setting an error code & keep ECU control.

Can you think of a circuit to do that? (keep things simple till they work (the little steps))

FYI: The ECU verifies the 15 Ohm are present and then (in theory) feeds the t-stat voltage in 2V volt steps or so -It is called a MAP controlled t-stat, as in the graphic bellow: (It could also be doing it by timed pulses!) either way our interest in the 3 conditions above prevail.
Image
 
A
#52 ·
Cruze CTRL said:
1. All we need is the ability to feed the t-stat heat element 12v when we need to override the ECU.

2. The ECU needs to be fooled into thinking it's still connected to (at least?) a 15 Ohm resistance.

3. When we back off (0 Volt to the heater) the ECU must be taken off the dummy 15 ohm resistor to be re-connected with the real one (inside the thermostat) to avoid setting an error code & keep ECU control.

Can you think of a circuit to do that? (keep things simple till they work (the little steps))

FYI: The ECU verifies the 15 Ohm are present and then (in theory) feeds the t-stat voltage in 2V volt steps or so -It is called a MAP controlled t-stat, as in the graphic bellow: (It could also be doing it by timed pulses!) either way our interest in the 3 conditions above prevail. View attachment 302469
Click to expand...

the problem is in the original schematic on this thread that ecu doens't controll the thermostat as intended. i want to correct that with my schematic. in case of high temperature on the engine, the thermostat is relying only on the buck converter, and i don't find this safe. so, i want ECU, if coolant hits 108 degree celsius, to open the thermostat as if this schematic was not installed.
so, this is my new schematic:

Preview of gallery image.

a14neltherm.jpg

new schematic thermostat control

i put 2 x 750ohm 5w resistor in parallel(results a 375ohm resistor) to fool the ECU and i'm using a pnp transistor to switch the signal from ECU(-) to OUT+ of the buck converter, to override the buck converter. so, if ECU want to gice full 14 volts to the thermostat, it can!!
so, the thermostat is running now with continuous voltage outputed from buck converter and pulsed 14 volts from ECU.
very simple.
i'm gonna test the schematic today in my car. on bench is working fine.
 
A
#54 ·
Got back home from test.
First of all, i have an 80°C thermostat from Mahle(see my youtube page, same username as here, adaniel69). So, i cannot tell how is working on an original 103°C thermostat.

In my case, yes, it lowered the working temperature and with A/C on is very good i would say(2-3°C variation when driving and parked with engine on). But, without A/C, it goes to more than 90°C, i don't know exactly, maybe up to 108°C as without this modification. I didn't waited enough.
But, with the original thermostat it is an improvement, at least while driving!

The only solution here is to control the thermostat by the temperature.... Some relay/transistor controlled by the coolant temperature...
 
A
#56 ·
ok. so, my final solution is to replace the thermostat. i've took out the core from a Mahle TM 37 80 and installed into the original Mahle 36 103(original in our engine). and for the electronic control part, i've installed in parallel with the engine temperature sensor a circuit composed by a thermal switch(60 degree celsius) in series with a 365 ohm resistor, in order to show to ECU that the temperature is higher and so is engaging the fan and opens thermostat electronically!
this way, ECU sees this:
real temparature...............ECU sees
70........................................93
72........................................94
75........................................96
77........................................97
80........................................99
82........................................100
85........................................102
88........................................104
90........................................105
93........................................108
95........................................110
all values are in degree Celsius and aproximate values!
 
A
#61 ·
@DIYguy the problem with the 80°C thermostat is when the engine is running but the car is not moving(ex. On traffic light, waiting for somebody...). In this situation, coolant goes up to 108°C, until ECU sends command to open the thermostat electronic and starts the fan. As long as the car is moving, the temperature is about 80°C. So, to avoid this, i installed in parallel with the engine coolant temperature sensor a 365 ohm resistor that kicks in when the engine has reached a certain temperature(thermal switch). This way, when the engine has reached about 93°C(real), over OBD i see 108°C and the fan is starting and thermostat opens electronic!
I will post some videos on my YT channel with the same username as here.
👍

PS: you have to understand that this thermostat is working mechanically(partial opened, even when more than 100°C) and electronic(fully opened(even on 0°C).
Even with the 80°C thermostat, without the electronic part, coolant can boil(>108°C)!
 
D
#62 · (Edited)
adaniel69 said:
@DIYguy the problem with the 80°C thermostat is when the engine is running but the car is not moving(ex. On traffic light, waiting for somebody...). In this situation, coolant goes up to 108°C, until ECU sends command to open the thermostat electronic and starts the fan. As long as the car is moving, the temperature is about 80°C. So, to avoid this, i installed in parallel with the engine coolant temperature sensor a 365 ohm resistor that kicks in when the engine has reached a certain temperature(thermal switch). This way, when the engine has reached about 93°C(real), over OBD i see 108°C and the fan is starting and thermostat opens electronic!
I will post some videos on my YT channel with the same username as here.
👍

PS: you have to understand that this thermostat is working mechanically(partial opened, even when more than 100°C) and electronic(fully opened(even on 0°C).
Even with the 80°C thermostat, without the electronic part, coolant can boil(>108°C)!
Click to expand...
I am very well aware of how the cooling system and ECM control algorithm works, thanks.
I must point out that you are incorrect or at least a bit misleading about it being able to electronically open at 0°C.
If powered on at full battery voltage the stock thermostat will open at about 76°C per the FSM and many other sources, not 0°C. Sorry, it just is.
The reason the temperature continues to rise despite having an 80°C thermostat is because the radiator fan is off and there is a lack of airflow through the radiator.

If the water exiting the radiator is at the same temperature (or higher) than the thermostat's setpoint, no matter what it may open at it is physically impossible for the water to cool the engine.
This is thermal physics in action, a basic law of nature, and is how the Cruze cooling system works, unfortunately.

I have even written about the fact that the aero shutters on some cars (mine for example) will happily choke off the radiator airflow even at highway speeds until the engine is running at 108C, and this is 100% by design.
You could literally remove the wax motor element from the thermostat entirely and it would still run that hot at a long stoplight because only about then would the fan turn on.

However you get the fan to turn on earlier is up to you, but as long as you can make it happen, it will work well.

I and several hundred other people have proved this concept beyond any doubt on another car type that had a disgustingly similar coolant temperature control scheme (Saturn).
It exhibited almost identically the same behavior (gee thanks GM...).

Adjusting the thermostat downward is a part of the solution, but it is emphatically not the whole solution.
As long as your switched resistor solution does not set codes or run afoul of emissions monitoring, go for it... :)
Sounds like an interesting idea actually.
However I can tell you (because I tried it) that leaving a resistor in place all the time (not switched) WILL set error codes ("improbable temperature").
So if switching in at a certain temperature and not before does the trick, more power to you.
 
A
#65 ·
@raforr i didn't had P0128 or any other code after switching to 80°C element. But, i think, with what i've explained(switched resistor in parallel with engine temperature sensor), you could get rid of that fault code, because ECU sees about the right temperature. Also, i cut a little bit from the rod of the heating element(about 1.5mm), to rise the temperature a little bit!

@DIYguy yes, you're right! Fan is important to run while the car is standing still with engine on. I'm happy with my modification. Of course, better is to reflash ECU with a modified software... I don't want to controll the fan external because it's more complicated than my solution. Anyway, i need to test it on longer trips. This is why i'm not posting it yet on my YT channel.
PS: with 0°C, i mean outside temperature, not water temperature
 
O
#82 ·
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