Coolant thermostat/temp questions

[Marksman762]

Hi everyone,

I've noticed a few issues lately and I think they might point to a faulty coolant temp sensor or possibly a thermostat. I've replaced the thermostat once, about a year and a half ago. I did not replace the temp sensor (had the wrong part, it turns out).

It's been super cold here lately, which could be part of the issue, but I doubt it. -18F this morning on the way to work.

I've noticed really crappy gas mileage the last few weeks, below 13 MPG. I've also noticed my temp needle likes to sit below the 210 mark normally, but will bounce around between just below and just above 210. I hooked up Torque through a bluetooth OBD scanner and am seeing coolant temps between 185-190F during normal driving. I'm thinking that's a little low. I do not have a check engine light or a pending code.

I just wanted to get some confirmation from better minds before I dive into a thermostat/temp sender replacement if it's not needed.

Let me know if there is any other info that could be useful.

Thanks everyone!

 

[JamesL3]

I'm fairly sure 190F is OEM spec. As long as you're not throwing a code, you should be fine.

 

[Chickenhawk]

Crappy gas mileage is mostly the winter gas blend and the fact it has been so cold the past few weeks on the prairies. (I am about 2 hours north of you.)

However, 180 - 190 is too cold for our platforms. It seems you have caught it before it does too much damage to the cat. Plus, if the coolant temp sensor is starting to go bad, those aren't the correct readings anyway.

When thermostats go bad, they tend to go bad in the long term, staying a tick or two below center on the gauge consistently.

When coolant temp sensors go bad, they start to fluctuate up and down, especially on the highway when the gauge should otherwise be rock solid.

I think your analysis of the problem is a good one. Replace the coolant temp sensor.

 

[JamesL3]

That's strange... I swear the thermostats they're selling on RockAuto are 190F OEM spec. Could they be wrong? I'll have to look into that. If that's the case, they sold me some useless junk. I guess it's good that it's been too cold to install!

 

[Blckshdw]

My truck never runs cooler than 195, once it goes closed loop. When my previous t-stat went bad, I was running around 185 as well.

 

[Mooseman]

I first replaced my thermostat with a Stant and found that it was cooler. Put in an ACDelco and it's a tick higher.

 

[meerschm]

View attachment 31592

For reference: my indicated obd coolant temp levels out between 201 and 206 or so f for this no-load commute to work. (on my 2003 I6)

I am pretty sure the thermostat I put in was from Rock Auto. likely the 190 spec.

 

[Marksman762]

Driving home today I noticed the following:

Torque showed between 185-188.6F. It moved between exactly 185, 186.8, and 188.6 degrees. Nothing in between for at temp driving. This was both highway and stop and go in town, didn't really matter what I was doing. At 185 the gauge would read slightly below 210. At 186.8 it was right on 210. At 188.6 it was just a hair above 210. Every minute or so it would bounce to one of those points and I would see the temp change on Torque.

In any case, as far as I understand, the gauge should not be reading below 210. I think I'll be replacing both the temp sensor and thermostat. I don't recall ever seeing any indications like what I have been, something isn't normal.

 

[TByuri]

Don't have the torque app yet but I just installed a new ac Delco thermostat and coolant sensor and my gauge reaches slightly to the left of 210 but not reaching the first tick to the left.

Hope that's normal because those were brand new ac delco and so tough to install for me.

 

[Wooluf1952]

Don't have the torque app yet but I just installed a new ac Delco thermostat and coolant sensor and my gauge reaches slightly to the left of 210 but not reaching the first tick to the left.

Hope that's normal because those were brand new ac delco and so tough to install for me.

The t-stat is a PITA to change for most of us. Some go thru the wheel well.

 

[Robbabob]

my gauge reaches slightly to the left of 210 but not reaching the first tick to the left..

 

[CaptainXL]

The t-stat is a PITA to change for most of us. Some go thru the wheel well.

I really don't see what's so hard about it. Just remove the alternator and its right there.

 

[The_Roadie]

I really don't see what's so hard about it. Just remove the alternator and its right there.

There's the problem. Lotsa owners are intimidated by removing the alternator. Or taking off the serpentine belt. The thermostat should have been put right up front and top like in many old cars. Two bolts and ten minutes, and done.

GM, in their infinite design skills to maximize long-term maintenance costs to help the dealers out down the road, put it in a crazy spot so the hourly flat rate could be inflated.

I just refuse to believe design engineers could be so dumb ..... that would be like the body sheet metal interfering with the removal of the upper control arm bolts because nobody on the suspension design team talked enough to the body design team and they never noticed it on the assembly line because the body was put on after the chassis was completed. Nah....never happen......

 

[CaptainXL]

Well we could gut the existing thermostat. Take the spring and valve out so that is flows through. Then cut the lower hose halfway to the radiator and install something like an inline thermostat housing. But would it get hot is the question. Just feeling kind of ingenuitive today I guess.

JEGS Performance Products 53260 In-Line Thermostat Housing : Amazon.com : Automotive

 

[Mooseman]

Because it's a reverse flow system, this probably wouldn't work as the inline thermostat would only see the cooled coolant. Interesting thinking though. But you still have to get to the thermostat out to gut it and re-install it so unless you change it on a regular basis, it wouldn't be worth the cost or effort.

 

[CaptainXL]

Wait. Reverse flow? So the coolant flows from the radiator and towards/through the thermostat into the block?

Well if that is the case why can't we install a thermostat on the top of the engine outlet hose? I am sure we can jimmy something up like that.

 

[Wooluf1952]

I really don't see what's so hard about it. Just remove the alternator and its right there.

Maybe my '03 was assembled differently. The AC hoses are routed so that they are in the way. It's a PITA, to get the socket to the bottom bolt of the alternator. And getting the bolt started again is also a pain.

But, you are correct. Two bolts and a hose clamp to actually change the t-stat.

 

[Mooseman]

Are you guys removing the fan and shroud? I can change my alternator in 20 minutes flat since I have efans. No problems getting to the bolts. I just use a ratchet wrench for all three.

 

[TByuri]

No didn't remove the fan parts but that lower alternator bolt with the hose in the way took forever.

My bolt was on there tight as well. And I had no leverage at that angle as well.

 

[seanpooh]

It's a pain since the AC line is in the way when backing out the bottom bolt of the alternator. Not a big problem but just a pain, something a ratcheting wrench can be a big help.

I went through the wheel well which is more of a pain than removing the alternator...

 

[Wooluf1952]

Are you guys removing the fan and shroud? I can change my alternator in 20 minutes flat since I have efans. No problems getting to the bolts. I just use a ratchet wrench for all three.

It's a pain since the AC line is in the way when backing out the bottom bolt of the alternator. Not a big problem but just a pain, something a ratcheting wrench can be a big help.

I went through the wheel well which is more of a pain than removing the alternator...

Good to know. I didn't have ratcheting wrenches when I changed mine. I have a set now.

 

[CaptainXL]

I just bent the AC line a bit to gain access.

 

[JerryIrons]

I have pulled my alternator a few times, and I can concur that the ac line makes it more difficult than it should be and is in the way for the one alternator bolt. Possibly only trailblazers with rear ac run into this? Once you do it though it, it's not so bad the next time you know what to expect. That first time though I was swearing at gm.

 

[Billdaman]

There's the problem. Lotsa owners are intimidated by removing the alternator. Or taking off the serpentine belt. The thermostat should have been put right up front and top like in many old cars. Two bolts and ten minutes, and done.

GM, in their infinite design skills to maximize long-term maintenance costs to help the dealers out down the road, put it in a crazy spot so the hourly flat rate could be inflated.

I just refuse to believe design engineers could be so dumb ..... that would be like the body sheet metal interfering with the removal of the upper control arm bolts because nobody on the suspension design team talked enough to the body design team and they never noticed it on the assembly line because the body was put on after the chassis was completed. Nah....never happen......

Bill, I was present during the design phase of these vehicles. I wouldn't give GM credit for sinister intentions for placement of the T stat, or I should say don't give them that much credit. This and many other similar issues from the time frame of 1998 - 2007 (like the fact that on my DTS you must pull the tires and drop the front fascia to replace the headlamps) resulted from the fragmented structure of GM at the time. GM power train did what they pleased. Only the Manufacturing engineers could put a stop to a particular design if it added labor or was considered a "no build". Then after a lot of battles things might move to a better location, but this was purely for manufacturability, not serviceability. Given that the hose would be right in place to connect to the rad before body chassis marriage this was not a problem for the assembly plant, so no one stopped it.

During the 1998 to 2007 time frame Manufacturing had a strong say, but the service engineers had little say, mostly because they were all contract employees, and in some cases that they never showed up to all the meetings or just didn't care. Alcohol could sometimes be a factor! Typically they had more work assigned to them that they could handle, and miss just a single design release and it became too late. Then others from their team could stay gainfully employed again on contract writing the service procedures to get around the cluster &*%# design that made it through. Now the team I was on would always consider serviceability, but not all teams were like that and the original GMT 360 team that approved this design was definitely just focusing on what it took to assemble the body to chassis on a 47 vehicle per hour line. That's the story as I see it.

 

[Wooluf1952]

I have pulled my alternator a few times, and I can concur that the ac line makes it more difficult than it should be and is in the way for the one alternator bolt. Possibly only trailblazers with rear ac run into this? Once you do it though it, it's not so bad the next time you know what to expect. That first time though I was swearing at gm.

I have a SWB Envoy. So, .

 

[meerschm]

on the issue of engineering for servicability, the driver here is the consumer.

does anyone really look at servicability when making a purchase decision? has anyone looked at where the thermostat is before buying a new car, and walked away if it was hard to get to?

the most, (I suspect) would be comparison at Edmunds total cost of ownership, that takes a shot at expected maintenance cost. kind of an indirect measure, but suitable for most comsumers.

we seem to not do a good job at this, like the fact that energy efficiency of houses does not directly influence prices. (location, location, location) who cares if it costs an extra thousand dollars (or two) a year to heat and cool?

Actual ease of service is not a top concern, when considered with long life, efficiency, and flexibility of a platform to be marketed in world markets.

 

[Marksman762]

Good discussion!

Getting back on topic I scanned another Trailvoy from a buddy who just had his thermostat replaced. I was getting a solid 196+ for temperature readings.

Based on that and what everyone here has said I surely have a problem. The way my needle bounces around it's probably the temp sensor, but being that I'm running a good 15+ colder than I should be, it could be a thermostat too. I'll just replace both.

Now I have to decide if I want to do the job in my cold garage, or wait until I drive 8 hours home to a heated garage for Christmas.

 

[Sparky]

I'd be tempted to wait on the warm garage this time of year!

The 190 degree temp on the tstat is the "start opening" temp, so running temp is almost always a little higher than the temp on the tstat.

I replaced my alternator a few years ago (bearings were shot). I didn't think it was a terrible job, at least compared to some other projects I've worked on.

FWIW, my Trailblazer gauge reads about 1 tick left, temp scanned via Torque Pro is around 195. Original tstat, by the way, not bad for going on 14 years and over 190k miles

 

[Creekapeake]

Hopefully this will save someone from having to install a Thermostat 2x...

When you change your Tstat (and yes a pain) remember to put some grease on the o ring gasket so IT WILL STAY IN PLACE!!!

I learned the hard way. Installed the Tstat, put everything back together... and it leaked. The problem was that gasket did not seat properly when putting the new one on.

Something so simple cost me about another 2 hours of my life.

GP

 

[Marksman762]

Hey everyone,

I replaced both the thermostat and the temp sensor and am seeing normal readings again. Temps are close to 200 degrees and I'm not seeing any movement on the gauge anymore. I used an AC Delco thermostat this time, as the factory packaging lists a higher temp than most of the aftermarket's.

Unbelievably, the job only took me two hours this time...

Thanks for everyone's advice!

 

[IllogicTC]

I just came in here looking to read up a little on problems/solutions with thermostats, and learned quite the lesson in billdaman's post!

I would also imagine that as manufacturers try to cram more and more crap under the hood, and in some cases try reducing overall car size, crap like the thermostat placement happens, too.

88 Dodge Ram, had a 318 motor, radiator, battery, brake system, and a little computer off to the side under a full-size hood.

Now we have all sorts of modules, an A/C system (wasn't on the Ram I had but it couldn't have taken a whole ton more space since I crawled INTO the engine bay to do plugs), super-mega-fancy air systems with the stupid air pump (as compared to just a donut on top), all sorts of other stuff... which would also explain why the air filter is laid halfway into the wiper fluid tank! Never understood that, I feel like it's not getting optimal surface area exposure.

I guess a mix of what billdaman described in improving manufacturing time/cost (to stave off what happened anyway, I would bet [bankruptcy]) and a need to cram all these emissions and electronics and other systems into a bay that while not small, isn't a full-size pickup bay or something. Kinda crazy, too. My line at my workplace only builds maybe 47 windows an hour - and that's just going from sticks of vinyl to the basic frame and sash, not dropping glass or packaging for shipping and only getting maybe $150-200 for a basic (no frills, not big) window). I couldn't imagine doing whole vehicles.

Now that I'm done rambling off-subject - my thermostat gauge fluctuates a bit, too. It's tiny little increments, up and down, all around the midway mark, and once it's fully warmed up to the core, it just stays on 210 solid. Potential problems, or normal during the final bit of warmup?

 

[Mooseman]

It's probably normal. The PCM does a lot of "filtering" of the actual temp data to not overly alarm unsuspecting owners. You could get a hold of an ELM27 and the app called Torque for Android if you want to see the real temps. They're pretty cheap on eBay.

 

[Frankd1]

I replaced my t-stat and coolant temperature sensor not too long ago as well. My temp gauge was reading 3 ticks to the left of center - I verified with my laptop scanner and the temp was showing 180.

I used an ac-delco thermostat part #15-11006, ac-delco temperature sensor part #213-936, I also replaced the upper and lower hoses with new Gates hoses and completely flushed all the coolant until it was draining clear distilled water. Refilled with fresh dexcool to the proper ratio.
My temp gauge shows 1 tick left of center (200deg) and sometimes a tad higher (between 1 tick left and center - 205deg), I will verify the exact temperature with my scanner tomorrow but this is good enough I think.

I removed the alternator, battery and battery tray to give more room. The lower alternator bolt was a pain in the ass but I used a stubby 15mm wrench to break it loose initially and then used a ratcheting 15mm wrench to work it out the rest of the way. Once I made contact with the AC line I was able to remove it the rest of the way by hand by angling the alternator slightly (loosened top bolts) and putting a bit of pressure on the AC line to move it out of the way slightly.

 

[dmanns67]

When coolant temp sensors go bad, they start to fluctuate up and down, especially on the highway when the gauge should otherwise be rock solid.

That is the exact issue I noticed about a week ago when driving down the highway. My TB would be completely warmed up and when I would get on the throttle and my RPMs raised to about 3-3500K, my temp gauge would drop until I got off of the throttle. Might as well do the t-stat while I am at it.

ac-delco temperature sensor part #213-936

Where did you find the sensor with that part number? I did a quick google search for that AC Delco part number and the only thing that comes up is for AC Delco crankshaft position sensor.

 

[CaptainXL]

Where did you find the sensor with that part number? I did a quick google search for that AC Delco part number and the only thing that comes up is for AC Delco crankshaft position sensor.

Google is normally your friend but when it comes to GM maintenance parts I use the ACDelco catalog.

ACDelco Parts

SENSOR ASM-ENG COOL TEMP
Part Number: 213-4233

Remember Frank has an 03. After 2005 stuff under the hood changed a bit. Different connectors for sensors, returnless fuel system, different coils and so on.... Never go by what someone else says unless they are the same year as you. Even then I would still double check.

 

[Sparky]

Yeah wasn't there one year that the coolant sensor was on the back of the engine or something really weird? I seem to remember someone on here or the OS trying to find his sensor and no one believed him that it wasn't next to the tstat at first.

 

[JerryIrons]

My 06 ext I6 has the coolant sensor in the back of the engine, and it was a big enough pain to change out that I didn't bother at the time of my tstat and hose change out. I wasn't that guy, but I will say personally I looked forever for my sensor until I found it at the back, I almost couldn't believe it myself. IIRC, there really aren't any instructions in the service manual on changing it out either, other than, "replace sensor".

 

[mykals1]

I have been chasing a P0014 code on an 02 tb I6 I just bought this truck and I has been sitting for some time,i replaced the t-stat with a stant aftermarket plus put a CTS in while I was there, hooked up my scanner temps went from 176-190 max never getting any hotter,yesterday I replace the clutch fan and did some more readings now truck runs 196-198 by scanner and gauge in truck is very slightly to left side of 12 oclock,still have engine code p0014,and cant seem to get it after replacing cam solenoid ,pigtail, cam sensor but I think we have temp right now and when I took off intake resonator I had a lot of water and some milky oil in both the hose to valve cover and under oil cap

 

[hullman8]

I have noticed that my temperature gauge (for what it is worth) has been running about a quarter to the vertical during the colder temperatures this winter. It does not jump around or vary with coasting or acceleration like others have noted, but will not warm all the way up to normal on my stop and go commute in the cold weather. Since this has been happening, the heat has not been getting as hot as usual either. Does it sound like a thermostat and radiator fluid change to you guys? That's what I'm understanding from reading this thread. Oddly, SEL just popped on this morning (a day or two after the arctic vortex).

 

[CaptainXL]

View attachment 18657

Can you do this again please? Only this time note the outside temp and let the truck idle until it warms up fully. My engine is taking a long time to heat up. I think its a stuck open thermostat but there doesn't seem to be any definitive tests other than comparing with a known good.