Thermostat modified for cooler operating temps.

[BigLee]

Some time back, I mentioned modifying a stock thermostat housing to adapt to a conventional thermostat to lower operating temps.
Yes, I know all the arguments about hotter engines supposedly delivering more economy, and possibly even power, and that the tune can be modified to cool the engine by altering the heater duty cycle.
But the heaters in these thermostats have enough problems with durability without ramping up its on-time to pretty much full time...

Basically all I did was gut a stock thermostat housing and cut/grind a std. thermostat to fit into the housing, use RTV sealant to seal it to the housing, and use the original retaining clip to hold the new thermostat in the housing.
I have access to several failed warranty claim thermostats to play around with, so I was able to modify a couple while still driving on the stock one.

Now since the modded stat no longer has a heater in it, I used a resistor connected across heater connector plug to satisfy the PCM that the circuit is ok.
I expected that a code might still pop up over low temperature or heater diagnostics, but I've been driving on the modded stat for over 6 weeks now, and no codes have appeared so far.
Apparently the criteria for triggering a fault code arent as strict as I thought they might be.
Typical operating temps vary slightly from 187-192 deg. F, with 189-190 deg. being most common.

Keep in mind that the 1.4l uses an inlet-side based thermostat, which regulates coolant from the "cool side" of the engine, as opposed to most older engines that regulate coolant as its leaving the engine on the "hot side".
Now a thermostat that regulates from the "cool side" is rated about 10 deg or so cooler than the what the outlet side will actually end up being.
The outlet "hot" side is also where the engine coolant temp sensor is still mounted, and that includes the 1.4.

So basically on the 1.4, you'll get outlet side temps that are aoroxamately 10 deg. hotter than the thermostat's rated opening point.
My new stat's rated opening point is 180 deg.F, resulting in about 190 deg. outlet temps.
This outlet temp will vary slightly depending on how much load the engine is under at the time. Under higher loading the outlet temps might get up to 192-194 deg., while decelerating/coasting, it may drop to 186-188 deg.
This is normal, and happens with the stock stat as well.

Pics:

 

[BigLee]

Little modification is needed to the thermostat housing itself. You will have to grind enough plastic from where the heater plugged in, to make room for the top of the new thermostat. Or, you can completely cut the boss for the heater element out as I did on this one. I did put some sealant over the cut area, just to help ensure coolant dosnt possibly seep along the electrical prongs.
The heater connector is no longer plugged into the thermostat housing, and the resistor plugs into the harness connector.
I'll try to get a pic of this tomorrow.
Including a new gasket, I have less than $20 each in these thermostats.

 

[Stew]

Interesting. I've not seen a stock housing taken off, if you could maybe post a pic or two an unmodified one to see exactly what wires and stuff you're removing. Cheers!

 

[Italianjoe1]

How much lower will this pull temps than just tuning the stock t-stat to run at 180 all the time? Real world gains, aside from poorer fuel economy?

 

[BigLee]

Interesting. I've not seen a stock housing taken off, if you could maybe post a pic or two an unmodified one to see exactly what wires and stuff you're removing. Cheers!

I'll try to get some pics of a stock thermostat this weekend.
Basically there's just a 2 wire connector on top of the thermostat, and on the inside the wax pellet with the heating element, there are two prongs sticking out the back that plug into a socket in the center of the plastic housing.

 

[BigLee]

How much lower will this pull temps than just tuning the stock t-stat to run at 180 all the time? Real world gains, aside from poorer fuel economy?

It will pull it down to whatever temp thermostat you choose, plus roughly 10 deg. F

My first modded piece used a 192 deg. Stat, and it netted about 200-203 deg. outlet temps.

Potential benefits include a possibly lower detonation threshold, longer life of plastic parts, hoses and seals, such as those in direct contact with coolant, like the coolant outlet, surge tank, radiator, ect.
Especially if combined with an auxiliary cooling fan switch, which I described in a previous thread over a year ago, and a pressure cap with a lower psi rating.
There are direct replacements caps available in 15 and 9 psi.
I'm currently running the 9 psi cap.

As for fuel economy, I've noticed no detectable drop in fuel economy, over multiple tanks, and yes, I've been watching carefully.

 

[BigLee]

Interesting. I've not seen a stock housing taken off, if you could maybe post a pic or two an unmodified one to see exactly what wires and stuff you're removing. Cheers!

My apologies for not getting to this sooner.
I hope this pic helps you.



On the right is a stock, fully assembled thermostat.
On the left, a stock housing with the valve, wax pellet/heater asy. removed.
If you look into the center of the housing, you can just see where the two pins for the heater plug into the housing.
The heater is integrated into the wax pellet.

The clip that holds the valve asy. in is held in place by spring pressure. To remove, push down on the retainer and rotate until it clears the plastic tabs.
Be careful, the retainer has some pretty sharp edges, so dont let it cut you. Leather gloves are recomended.

 

[skurtov]

The thermostat is electronically controlled. Can lower operating temperatures with a tune

 

[BigLee]

The thermostat is electronically controlled. Can lower operating temperatures with a tune

Its partially electronically controlled...
It's still a conventional wax pellet operated thermostatic valve, but with a heating element added to lower operating temps under heavy load conditions.
It's pretty common for heater element failure to occur in stock form.
If you keep it on most of the time with the tune, chances are you'll likely find much more frequent failures...

 

[JTee2017]

Its partially electronically controlled...
It's still a conventional wax pellet operated thermostatic valve, but with a heating element added to lower operating temps under heavy load conditions.
It's pretty common for heater element failure to occur in stock form.
If you keep it on most of the time with the tune, chances are you'll likely find much more frequent failures...

I like this idea especially given that both the 1.4L and 1.8L engines are set up to run so hot. Anything under 200F would be an improvement.
A couple things though. Have you noticed or connected an OBD scanner to the car to determine if it is running any richer in fuel mixture since the ECM would sense a cooler running temp?
Also, could you post what brand and P/N thermostat you used along with the resistor value you used to resolve the lack of the heater?

I think this mod plus the radiator fan mod are great ideas. I would think this would extend the life of the coolant reservoir and other cooling system tubes and hoses as well. All that plastic in a cooling system does not make for durable long term operation, even though it is supposed to be able to handle it.

 

[BigLee]

I used a thermostat for a 98-02 Cavalier 2.2L OHV (LN2).
Autozone/Duralast part# 4028. 180 deg.F is the stock temp.

It is 44mm in diameter, and must be trimmed down to roughly 41.5-42mm to fit inside the housing.
I marked a scribe line ~1.5mm in from the edge of the thermostat, and used an angle grinder with a sanding wheel to trim it down.
Dont forget you'll need to trim a bit of plastic out of the center of the housing to make room for the top of the new thermostat to clear, so it can sit in the bottom of the housing.

Use plenty of RTV sealant between the outer edge of the thermostat and the housing. Since the sealant will be rather thick, I'd give it 3-4 days curing time before installing it on the engine.

If you install it before curing is complete, coolant bias pressure at the thermostat might displace the sealant, causing bypass flow, and an engine thats very slow to warm up. Even worse than they already are...

I use the Torque app, and have consistently noticed my car goes to closed loop as soon as the engine reaches 130 deg. F. With an indicated A/F ratio of 14.7:1 at idle and cruise.

 

[JTee2017]

I used a thermostat for a 98-02 Cavalier 2.2L OHV (LN2).
Autozone/Duralast part# 4028. 180 deg.F is the stock temp.

It is 44mm in diameter, and must be trimmed down to roughly 41.5-42mm to fit inside the housing.
I marked a scribe line ~1.5mm in from the edge of the thermostat, and used an angle grinder with a sanding wheel to trim it down.
Dont forget you'll need to trim a bit of plastic out of the center of the housing to make room for the top of the new thermostat to clear, so it can sit in the bottom of the housing.

Use plenty of RTV sealant between the outer edge of the thermostat and the housing. Since the sealant will be rather thick, I'd give it 3-4 days curing time before installing it on the engine.

If you install it before curing is complete, coolant bias pressure at the thermostat might displace the sealant, causing bypass flow, and an engine thats very slow to warm up. Even worse than they already are...

I use the Torque app, and have consistently noticed my car goes to closed loop as soon as the engine reaches 130 deg. F. With an indicated A/F ratio of 14.7:1 at idle and cruise.

Thanks. . that detailed info is what is very helpful. I have the Torque Pro app on a tablet and a cell phone I use exclusively for car and other apps of that type. Wow. . . closed loop occurs at 130F is interesting but expected for good MPG.
What value resistor did you use to fake out the lack of the heater element?

 

[BigLee]

Yeah, they want these cars to get into closed loop ASAP, for both fuel economy and emissions reasons.
Even the mid to late 80s fuel injected GMs would typically go closed loop at 135-140 deg.F....

I used a 44K ohm resistor.
The heater element is 14-16 ohms.
So any resistance above about 16 ohms is accptable.
I dont think I would go much above 50K though.
Basically the PCM looks for the presence, or absence of 12 volts on the ground circuit.
If it isnt grounding the heater (heater off), then it expects to see roughly battery voltage on the ground wire, and no voltage on it if is grounding it (heater on).
All the resistor is doing, is allowing just enough current to flow to satisfy the voltage/no voltage expectations of the PCM.
I presumed I might get a heater fault code anyway, because I figured the PCM would perform a "cause and effect" diagnostic by testing for a coolant temperature drop once it reaches 217 deg. or so, but I guess it cant run that test if the coolant never gets that hot.
I also thought it it might trigger a "low coolant temp" code, but I guess ~190 deg. is hot enough to prevent that.
The threshold is probably still 180 deg., like older models.
Needless to say, you wont get the full benefit of this thermostat mod without the auxiliary fan switch mod as well, because at low speeds, stop-n-go driving, or parked, the coolant temps would climb until the PCM decided to turn the fans on.

Here is a pic of the resistor setup I'm using.
I pulled it out of the plug a bit to show the pins i soldered on. Notice I covered it all with shrink tubing.
I keep a small zip tie over it so it cant fall out.

 

[JTee2017]

Thanks, I appreciate that info and the picture. About what I thought and good to know maybe a 22K to 47K resistor should work fine. I have a large supply of electronic parts from restoring 70's audio gear.

And, yes, I agree the fan switch mod to me is a must if an owner wants more durability for all those plastic cooling system parts and maybe the radiator and heater core too. I can see where it may be a bit too cool fir winter driving. For me. . so far the car is our summer day trip and run about hatch back. Wife doesn't care for riding on the Harley, so just a little Red Rampage for us to enjoy and not use much fuel.

 

[BigLee]

Just a little update on this.
I previously stated that these engines go to closed loop operation at around 130 degrees F.
Well, that was based on my experiences with older GM models. I noticed that the Sonic was always in closed loop at or above 130, but after watching more closely this last winter, I was shocked to find the car was going into closed loop in 30 deg F weather on a cold start in as little as 40-50 seconds, at coolant temps as low as ~65 Deg. F....... with a target A/F ratio of 14.7:1 WOW....
They dont mess around these days. I guess they've really improved the heaters in the O2 sensors, maybe even managed to get them to go "active" at a lower sensor temp than the older ones did. Used to be, the sensor had to reach around 600 deg. F in order to start working.