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Discussion Starter #1
Just curious about what operating coolant temps other 3.6 owners are seeing. I drove around today (50F ambient) with Torque Pro monitoring my coolant temp and it held pretty steady at 194F. The warm range was 190-200 and the fan doesn't turn on until ~215F. I'd much prefer to see it running 180-190. The oem t-stat is 180F so perhaps I need a new one? Has anyone replaced the t-stat? It looks like a bit of a PITA.
 

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Put that stuff away and stop looking for trouble, it will find you soon enough. About 10 deg above the thermostat opening temp is correct, with fan running, or the car moving, or both, otherwise it will be a little hotter and the fan will turn on as you've noticed.

The thermostat does not open instantly, it gradually opens from the rated temp toward maximum as the temperature increases. The operating temperature is partly responsible for your fuel economy, a hot motor gets better mileage than a cold motor because more of the heat stays in the combustion chamber to do work, instead of being absorbed into the surroundings to a greater degree on a colder motor.

Contrary to what is often said about cooler temps being better for the motor, this is not 1900s technology and metallurgy where temps had to be low to keep the cast metals from cracking up. This stuff is designed to operate at and last in the designated operating range. The not too distant cast iron motors were running fan-on temp settings of 240 deg. I'd be more interested in keeping engine oil cooler, than lower coolant temps, engine oil runs hotter than normal coolant temps, that's why some applications have oil coolers that use the engine coolant for that process, in the same manner that the transmission does.
 

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On a hot day with AC on I see it stabilize at about 203 which would match a 195 thermostat that takes 8-10 degrees to open fully. I run my other computer cars at 180-190 and everything under the hood lasts longer. You have a 180 ? Is it stock ? My manual says:
"Cooling System Thermostat Full Open Temperature 95°C 203°F"

Have a 180 for the CTS but am a little slowed by "Remove the upper intake manifold". Really ?

ps GM has been using 195s since the '50s
 

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Discussion Starter #4 (Edited)
Since mine is running 195 on a 50f day with a/c off, I'm quite sure it will be running 200-220f range this summer. I am a little concerned that the 10 year old t-stat might not be fully opening but since I'm changing the 10 year old coolant tomorrow, the t-stat will have to wait until I pull the plenum to clean the valves.

When I turbocharged my Toyota I tried 140,160,170 and 180 t-stats. OEM was 195 but that came out before boost. The 140 was too cold and the 170 proved ideal for that setup. Luckily changing the t-stat on a Toyota is almost as easy as changing a headlamp bulb... on a Toyota.

Thanks for answering my question.

ps, According to Stant the rated temp is when the t-stat starts to open, reaching fully open at 15-20 deg higher. I haven't removed my stat to inspect it but every aftermarket parts supplier that I've checked (half dozen) lists the oem stat as being a 180f.
 

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...I run my other computer cars at 180-190 and everything under the hood lasts longer. You have a 180 ? Is it stock ? My manual says:
"Cooling System Thermostat Full Open Temperature 95°C 203°F"

...ps GM has been using 195s since the '50s
It's a noble thought, but trying to keep the engine a little cooler is not likely to add longevity to much under the hood, because it is designed to fall apart for recycling and planned obsolescence purposes. One of the most shocking changes I noticed is the thin gauge wire switched to around the turn of the century, I posted pics of wires to a side marker light, far from a heat source on an 07 car that showed fraying of the insulation significant enough to create a short.

There was also leaded gas back in the '50s to go along with those higher temp stats in the applications they were in, to help save valve seats (particularly crack prone) and reduce knock risk. My dad was into building up motors and said that some cylinder heads would crack at not too much above 160 deg, so some could handle the heat and some could not. They also had pretty big radiators and wide open front ends for great airflow.


Since mine is running 195 on a 50f day with a/c off, I'm quite sure it will be running 200-220f range this summer. I am a little concerned that the 10 year old t-stat might not be fully opening but since I'm changing the 10 year old coolant tomorrow, the t-stat will have to wait until I pull the plenum to clean the valves.

When I turbocharged my Toyota I tried 140,160,170 and 180 t-stats. OEM was 195 but that came out before boost. The 140 was too cold and the 170 proved ideal for that setup. Luckily changing the t-stat on a Toyota is almost as easy as changing a headlamp bulb... on a Toyota.

Thanks for answering my question.

ps, According to Stant the rated temp is when the t-stat starts to open, reaching fully open at 15-20 deg higher. I haven't removed my stat to inspect it but every aftermarket parts supplier that I've checked (half dozen) lists the oem stat as being a 180f.
You confirmed with the specs you listed that the temps you are seeing are within normal operating range. It can be freezing and all that will happen is the thermostat will take longer to open and the coolant temps will stay closer to the minimum temp possible with a 180 deg thermostat and the coolant fan will likely never need to turn on. I believe the thermostat is designed to fail open from what I recall, you can replace it as preventive maintenance, but chances are very solid that you will see the same temps that are bothering you now with the new part.

I looked into a higher capacity radiator due to future plans and noted that the CTS-V radiator is a little more than .250" thicker than the CTS' radiator and considered getting one and swapping the tanks to make it compatible, but then Spectra saved me the trouble a short while later appearing to have done just that and for a very good price although I'd count the rows and fins per inch and compare them to stock to make sure (a must do), unless they're willing to provide them through contact. Stock core thickness is .630" to .710", Spectra lists 1".

The easiest option is to drill an extra vent hole in the thermostat of about 1/8" or so to allow more coolant to bypass while the thermostat is closed, that may help some but you have to be conservative to avoid a code from the motor taking too long to warm up. So you see, you are trapped at higher temps by the programming.
 

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Possible but would bet the computer is "all in" by 170 at least my other GM computer cars are. Is easy enough to monitor coolant temp and "closed loop" operation. If you have a full factory service manual might look at the cruise control and if there is a "drop out" temp.

Before diving in I need to know just how many gaskets & O'rings are required to change a thermostat ?
 

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Discussion Starter #7
You confirmed with the specs you listed that the temps you are seeing are within normal operating range. It can be freezing and all that will happen is the thermostat will take longer to open and the coolant temps will stay closer to the minimum temp possible with a 180 deg thermostat and the coolant fan will likely never need to turn on. I believe the thermostat is designed to fail open from what I recall, you can replace it as preventive maintenance, but chances are very solid that you will see the same temps that are bothering you now with the new part.

I looked into a higher capacity radiator due to future plans and noted that the CTS-V radiator is a little more than .250" thicker than the CTS' radiator and considered getting one and swapping the tanks to make it compatible, but then Spectra saved me the trouble a short while later appearing to have done just that and for a very good price although I'd count the rows and fins per inch and compare them to stock to make sure (a must do), unless they're willing to provide them through contact. Stock core thickness is .630" to .710", Spectra lists 1".

The easiest option is to drill an extra vent hole in the thermostat of about 1/8" or so to allow more coolant to bypass while the thermostat is closed, that may help some but you have to be conservative to avoid a code from the motor taking too long to warm up. So you see, you are trapped at higher temps by the programming.
I really just wanted to confirm that my temps were normal for this engine to help me decide whether to replace the thermostat. Thanks for the confirmation and the info on the Spectra radiator. Good tip on drilling the thermostat. I've actually done that before as well as using an old thermostat to make a flow restrictor for a big block Chevy that ran hot. The BB probably needed a bigger radiator but I was young and broke. I used to turn on the heat to help cool the engine. Luckily it was a convertible or those summer days in traffic would have really sucked!

There are fail-safe thermostats that mechanically lock open but they sometimes stick open during normal operation so I don't use them. According to Stant, normal thermostats can fail open, closed or in between. They also recommend replacement when coolant is changed. The difficulty replacing this particular thermostat helped make the decision against replacement for me. I'll probably wait until it needs replacement. FWIW my '08 Toyota that came with a 195 thermostat threw codes with the 140 but never with the 160+ stats.

So far this GM is proving to be very difficult to work on compared to previous Fords, Toyotas, Nissans, Subarus, et al. Luckily it has other advantages that make it worth some additional effort for simple maintenance and repairs.
 

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It's not really hard to work on at all compared to what certain repairs would be like if it were transverse, front wheel drive, in which case I wouldn't own it. I despise front wheel drive arrangements. I don't think the thermostat is that bad, it depends on the person. I heard the same about the high pressure fuel pump and the first demo I saw on it, the guy had the hood removed. I replaced mine (preventive) with the hood in place and didn't feel that bad about it. If you have the correct tools for the job it shouldn't be that much of a headache. I would prefer a thermostat that sticks open, you can continue to drive with that. I've had one start to go bad during a trip from FL to KS, where the temp needle started swinging too close to high. I keep tools in the car for long trips and pulled into a gas station and was able to take it out and keep moving.
 

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Discussion Starter #9 (Edited)
It's relative. I agree that it's not really hard but all the extra steps do take more time. On most of my previous cars headlamp bulbs could be replaced without tools in minutes instead of hours. Oil changes didn't require the removal of a large belly pan because they included access panels. Changing the thermostat required removing 2-3 bolts and nothing else. I agree with you about transverse V6 engines but in my experience transverse I4 engines were very easy to work on. At least it isn't mid-engined, that would really be a PITA to work on but also really fun to drive.
 

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OK ran a not very scientific test. Started the car cold/80F temp and read coolant on a digital gauge. Went up slowly but steadily to 195.8F then stopped for about two minutes, then went up very slowly to about 200 where I cut it off. Everything I see says it is a 195F thermostat that reached full opening at 203F (where my car stabilizes on the Interstate).

OTOH Stant & Rock Auto say their stock Superstat 46148 is a 180F which would match a 194F running temp

And on the gripping hand I have never seen a thermostat that took 23F from start to open full.

So must admit am confused and suspect the only way to find out is to replace with a Superstat and see where it cruises (over 60 mph the electric fan does not do much). Can always learn something new. YWTK

ps I have and really like two Buick Reattas - touchscreen coupe and a convertible, just need about 3 feet of extensions for one tranny bolt. 88 is now 31 years old and would drive anywhere. I tend to keep cars liked for decades so know running computer cars at 180-190F makes all of the hoses/ plastics/belts/ etc. under the hood last longer and is easier to AC. Of course these have been reprogrammed to bring the fans in at 185F.
 

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Discussion Starter #11
If the oem t-stat was 195 I would expect someone to make a replacement for it yet the only temp available is 180f. I suspect that there might be other reasons for the temps you're seeing. One possibility is a slow or sticky t-stat and another is Dexcool sludge affecting cooling system performance. If the overflow pressure cap leaks and air enters the system Dexcool can gel over time and turn to sludge which is then sucked from the overflow into the radiator. The possibility of which is why my engine is full of prestone flush and distilled water right now and will be for a few days until I flush it completely and re-fill with 50/50. Assuming that your coolant is original it is 8 years old now and Dexcool is only rated for 5 years. I'm looking forward to your results with the superstat (what I intend to use if and when).

FWIW, this winter my coolant was running between 185-190F max which points to a 180 stat.

I remember liking the Reatta a lot when it came out but I was in my 20's then so drove a '87 Mustang GT 5 speed instead. I couldn't have afforded a Reatta anyway. That Mustang was only about $12k new IIRC.
 

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You guys are over thinking this, the thermostat sets the minimum operating temp the engine is allowed to run at to keep the engine management parameters inside a tighter control range for fuel economy and emissions. The temp seen by the computer is what is sent by the sensor, which is upstream of the thermostat and subject to coolant that is absorbing heat from areas upstream of it for a cumulative effect. Without a thermostat the long term values saved for optimum fuel efficiency and engine performance would become short term values because the computer would be constantly changing them from wide temp swings in closed loop.

Here's a test for you, allow the motor to warm up to operating temp and as soon as it reaches 195-200 deg, raise the engine rpm to about 1500-2000 for about a minute and note what happens to the temp. There's a lot that determines the coolant temp seen at the gauge, flow rate is one of them. One of the efforts to reduce emissions and increase fuel economy ever so slightly, was to establish a low engine idle rpm which the 3.6L has.

The slower the coolant moves, the more heat it absorbs and it can do that incrementally in proportion to engine speed. Like most things, too much and too little can cause problems. Under drive pulleys for performance, equal higher coolant temps at idle, I know that from experience with them. Water has the greatest cooling ability by physical properties, put that in the system with a proper anti-corrosive, and anti-freeze treatment and temps will drop closer to the ultimate minimum attainable.

I can say as a result of having spent hours and hours of watching sensor parameters on a computer screen from data logging and making tuning adjustments and having upgraded radiators and swapped between copper and aluminum radiators that the only problem with the coolant system is Padgett and CaddyFred. I encourage changing the stat as a preventive measure though and wish that I had done so during one of the many occasions I've had the intake off. I'm telling you, keep looking for trouble when the engine light says there is none and you will find it.
 

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Great advise from Joseph The engineers at GM and Cadillac know what they are doing. Engines make heat to produce power there are many integrated items that keep the engine at a set temperature for a good reason. Changing one of them, (thermostat) will not go well with the computer.
 

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I am amazed at the biases on this forum, more than I've seen elsewhere. 200 rpm is a low idle nd was common a few decades ago as were radiator shutters. Back in the early 70's we were testing engines at GM at a steady 250F coolant. The issue was emissions and not longevity and until this century you needed about 600F exhaust temp for O2 sensor lightoff. Now we have wideband heated O2 sensors and the time in open loop is reduced.

The other difference is widespread use of synthetic oils (back in the day the EPA forced one manufacturer to repeat emissions testing when it was found that they had run the tests using synthetic oils that were not used in production.)

But the bottom line is that I could present a full dissertation but would be boring for most. Can we just agree to disagree and let members decide for themselves ?
 

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I am amazed at the biases on this forum, more than I've seen elsewhere. 200 rpm is a low idle nd was common a few decades ago as were radiator shutters. Back in the early 70's we were testing engines at GM at a steady 250F coolant. The issue was emissions and not longevity and until this century you needed about 600F exhaust temp for O2 sensor lightoff. Now we have wideband heated O2 sensors and the time in open loop is reduced.

The other difference is widespread use of synthetic oils (back in the day the EPA forced one manufacturer to repeat emissions testing when it was found that they had run the tests using synthetic oils that were not used in production.)

But the bottom line is that I could present a full dissertation but would be boring for most. Can we just agree to disagree and let members decide for themselves ?
I wouldn't describe it as bias at all. I'm trying to help by using the knowledge I gained from experience and spending a lot of money I would not have, had I known better. Some of the information I'm sharing here is the result of my own misunderstanding, and someone else having stepped in to explain why my thinking was incorrect, which helped me and I welcomed that along with all I've learned here.

You stated,

...And on the gripping hand I have never seen a thermostat that took 23F from start to open full.

So must admit am confused and suspect the only way to find out is to replace with a Superstat and see where it cruises (over 60 mph the electric fan does not do much). Can always learn something new. YWTK...
I thought it might help if I shared my thoughts regarding the matter, because I recognize the temp ranges you both are suspicious of as very much, normal performance. In my hot rodding efforts I had to pay close attention to coolant temps and often drove with a laptop sitting in the passenger seat displaying sensor readings, which displayed the range of temps you mentioned all day everyday I drove the car on a perfectly healthy coolant system. I have some older GM tech training manuals also, so some of my remarks are actual quotes from that material as well. No harm intended.
 

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Not a problem and I suppose the real way is for someone to take a stock thermostat and put in a pot of water on the stove and use an IR thermometer to see when it starts to open and opens full.

I've seen engines that would reach full opening and flow and the temp would just keep going up, usually ones with a four blade fan, no shroud, and cam & carb or a seven blade clutch fan with a bad clutch. Warmed up iron SBCs are really hard to keep cool in an H-body.

OTOH my 3800s have 180F Superstats and have been reprogramed to bring the fans in LO at 185F and HI at 189F. I find it easy to keep these engines cool and my 3.2 V6 Mercs (same engine in Crossfire) also stay cool.

So is really no reason the 3.6 LLT in the CTSC should not run under 200F and I would target under 190F. Just need to run some tests but am short of round tuits.

Also would help to know just how many gaskets/seals/o'rings I need to replace the thermostat. YWTK
 

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Drove the crap out of my CTS Sunday night getting home from work 1am.
I never noticed temperature increase before (normally around 85 deg C) but rolling into my garage the gauge showed around 110 deg C.

Also I noticed the oil pressure was a little lower than normal. Not much but enough to be seen on the gauge. I guess it is because oil temp was up and consequently viscosity down?


Sent from my iPhone using Tapatalk
 

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Discussion Starter #19
I worked on the car a little over the past few days. I flushed the cooling system, changed the oil and repaired years of neglect on the under-body panels done by mechanics who apparently operated on the "not my car" principle. Essentially missing/incorrect fasteners and holes enlarged by over-tightening of the bolts. I just added some washers on the belly pan bolts . I also installed a Fumoto oil drain valve but it's going to be a PITA to reach it without first removing the belly pan. At least I can stick some hose on the drain valve nipple and drain directly into disposal containers, skipping the drain pan step. I left the thermostat for another day. The car's running great, oil pressure is up a little and coolant temps are down a little.
 

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Some have cut a hole in the belly pan to facilitate easy operation of the valve.
 
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