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Cooler then stock is all you need.

That colder 40* or whatever works wonders on parts lasting longer.

That stock temp for the gen1 is why you all have the problems you all have. I don't know what GM was thinking when they did that. It certainly didn't do wonders for their profits.
Higher temps are for emissions. You get a cleaner burn at higher temps. That is why I believe the ECU is program to run at higher temps for cleaner emissions. If the temps run colder then the ECU may not reach its Optimum settings for proper emmisions. It may not make a difference to the daily driver but that is why the higher running temps. Too bad the failure rate of these parts is high from higher temps.
 

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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...
 

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Discussion Starter #84
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.
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. :)
180F.JPG
 

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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. :)
I see this as more a case of inadequate qualification testing rather than going cheap. Given the time frame of when this car came to market in the US, during development they were recovering from the 2008 meltdown, and were surely somewhat disorganized and likely short-handed.

So, while getting all the components tested and qual'd, as necessary for ramping production, they probably had a mixture of not enough test time to find all the vulnerable components, and not enough time to fix everything properly when they did - ie, to re-qual improved components - so some questionable pieces went into production. Coolant reservoirs and water outlets come to mind.

I'm not absolving them of blame, just trying to illustrate that, in many cases, it's not obvious where the weak joints are, so to speak, until you've got a significant number in the field, or lots of time spent in the test labs trying to identify all the marginal stuff, and trying to do accelerated testing, hoping to do a life-cycle test in only four months :)

There's an old saying: It's time to shoot the engineers and start production. They can't miss the start of the model year - they have to ship something to the dealers regardless of whether every last kink has been worked out or not. That's why it's not good to buy the first model year. Unfortunately, some of these problems lingered into the 2nd and 3rd model years :(

Doug

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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.
 

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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.
 

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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.
 

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IIRC.

You only need somewhere around 135 before emissions ready. Might be lower. Been a long time since I checked it out.
 

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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.
 
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