Bad Thermostat? Radiator heats up along with engine

[CaptainXL]

So I have been having this sneaky suspicion that my thermostat is stuck open. What peaked my interest was that the truck has been having a hard time heating up at idle when outside temps are under 35 F or so. What happens is I will start the truck up on an icy morning and let it idle for 20 minutes or so. When I check my scan tool the coolant is only at 160 F. Now I never thought this was a problem because after I get it out and start driving the coolant temp reaches about 200-204 F and is stable.

Over the past few days I have noticed when I downshift to 3rd and pass the temp drops pretty far. And tonight I went to idle it again and it did the same thing...never got up above 160 F or so.

But here is what I think is the damning evidence. After idling the truck tonight I waited till the temp got to 160 F again on my scan tool. Then I took the radiator cap off and took a temp reading using a probe thermometer. It read 150 F! What the heck? I think this means only one thing. The coolant in the radiator and engine are one complete circuit and the thermostat is open. Correct? Shouldn't the coolant stay cool until the thermostat opens at about 180F? Or is this normal for our vehicles. It would seem that the thermostat is not closing all the way yet opens enough to keep the engine cool and not go over 210 F.



Edit: Screw it. Just got new upper and lower radiator hoses, radiator cap, and ACDelco 15-11006 Thermostat for a total of $80. Im gonna fix this thing for good.

 

[meerschm]

good plan.

are you going to get the sensor too? it has been suggested, but to tell you the truth, I picked one up, but did not put it in. when I was into it, I realized I did not have the right tool, and figured if it was not broken to leave it be.

Are you going to pull the generator, or try to get tricky?

and of course, I have to ask about your water pump, belt and pulleys. my water pump went on the first long trip i took after the thermostat went. hindsight is a wonderful thing.

 

[Harpo]

Ill bet your t-stat looks just like mina did when you get it out.

I had a rubber seal stuck in the t-stat that stopped it from closing completley.
I also had the symtom , higher speed higher revs= lower temp.

 

[CaptainXL]

good plan.

are you going to get the sensor too?

Nah. I did it last year. The thermostat was replaced a few years ago by the previous owner. The receipt shows that an ACDelco tstat was installed so it will be interesting to see if that was really the case.

Are you going to pull the generator, or try to get tricky?

The easiest way in my mind to do it is to remove the alternator. I've already removed it once. It would be extremely tricky to torque the bolts and such going through the fender.

and of course, I have to ask about your water pump, belt and pulleys. my water pump went on the first long trip i took after the thermostat went. hindsight is a wonderful thing.

Belt and pulleys were done a year and a half ago. Now replacing the water pump is an interesting idea. They are only about $40 so I just might do that. Oh boy, gotta remove the fan clutch again. Ugh.

Ill bet your t-stat looks just like mina did when you get it out.

I had a rubber seal stuck in the t-stat that stopped it from closing completley.
I also had the symtom , higher speed higher revs= lower temp.

That's exactly what I think the problem is. I can form a mental picture and it seems the tstat is not closing all the way when the engine cools off. So would you say that this is more than likely from an incorrect install? If so I can blame it on the shop that replaced it last time.

 

[Bartonmd]

Yep, stuck thermostat.

BTW, why do you idle the engine so long? You know that cold engine wear is based on load and number of cycles at temperature, right? The faster you can get an engine heated up with the least number of cycles, without getting crazy on the load/throttle, the less wear you'll have. It's much better to start it up, let it idle for 20-30 seconds to let the oil get everywhere (maybe 2-3 minutes below 0F), then take off the drive easy, than it is to let it idle up to temperature. Letting it idle up to temperature has about the same wear as starting it up, putting it in gear, and putting your foot to the floor.

Mike

 

[CaptainXL]

Yep, stuck thermostat.

BTW, why do you idle the engine so long? You know that cold engine wear is based on load and number of cycles at temperature, right? The faster you can get an engine heated up with the least number of cycles, without getting crazy on the load/throttle, the less wear you'll have. It's much better to start it up, let it idle for 20-30 seconds to let the oil get everywhere (maybe 2-3 minutes below 0F), then take off the drive easy, than it is to let it idle up to temperature. Letting it idle up to temperature has about the same wear as starting it up, putting it in gear, and putting your foot to the floor.

Mike

Relax. It's not as if I idle the engine everyday. Just noticed the issue a couple weeks ago. I normally just get in and go but I noticed that the engine temp gauge would drop as I was passing people on the highway. It also was taking a long time to heat up when driving around town at 40 mph. I can heat it up driving around and then park it for 5 minutes and it will cool off again. So then I started my investigation a couple days ago.

 

[Bartonmd]

I'm not worked up or anything. Just sounded from your OP that you idle it for 20 minutes everyday in the winter. Not hard to believe, because my neighbor did that until I told him how bad sitting and idling a cold engine is.

Mike

 

[CaptainXL]

I'm not worked up or anything. Just sounded from your OP that you idle it for 20 minutes everyday in the winter. Not hard to believe, because my neighbor did that until I told him how bad sitting and idling a cold engine is.

Mike

No problem. Off the record I most certainly don't see any harm in idling an engine (other than for economical and environmental reasons).

When you read all the articles written by the pros they just tell you that starting a vehicle is where most of the normal wear comes from. This is provided you drive your car in a civilized unsporting manner.

I have never seen anything about how idling the engine puts wear on them. On the contrary, I have read evidence against that claim.

A properly tuned engine is meant to run weather it's at a stop light at idle or going 3K rpm passing a vehicle. It won't wear any more provided oil pressure is good and is tuned up and running well. Engines are meant to operate and not precariously wear away within their operating norms.

 

[Bartonmd]

No problem. Off the record I most certainly don't see any harm in idling an engine (other than for economical and environmental reasons).

When you read all the articles written by the pros they just tell you that starting a vehicle is where most of the normal wear comes from. This is provided you drive your car in a civilized unsporting manner.

I have never seen anything about how idling the engine puts wear on them. On the contrary, I have read evidence against that claim.

A properly tuned engine is meant to run weather it's at a stop light at idle or going 3K rpm passing a vehicle. It won't wear any more provided oil pressure is good and is tuned up and running well. Engines are meant to operate and not precariously wear away within their operating norms.

It's actually not so much starts, as it is cold starts. Wear is cycles at temperature. The colder the cycles are, the more wear. At operating temperature, there is almost no wear, but in cold temperatures, there is wear. Yes, it'll idle all day long, no problem, if it's warmed up. It's cold idling that's harder on an engine than cold easy driving, because there are more cycles at cold temperature, because idling warms up the engine so slowly, compared to driving. This is the case, mostly because pistons are aluminum, and cylinders (or cylinder liners) are usually steel, so when they're far away from operating temperature, there is more play between the piston and the bore, so the piston skirt tends to contact the bore more. Also, you're not burning nearly all the fuel, so the extra fuel is doing a little bit of washing the oil off of the cylinder walls, which also increases wear. When people say cold idling is better than taking off and driving, it's really only true if you pull right out onto a highway, or if you just drive hard when it's cold (which a lot of people do, my wife included). But even then, the TB has just shy of 100k miles, she has driven 95% of that, and it still only burns 1/2qt in 10,000 miles.

Mike

 

[CaptainXL]

Ugh. Were off topic. FWIW I have 128K on my truck and its not burning any oil. Can I interest you in some engine flushes? This fixed a whole host of issues for me.

 

[Bartonmd]

Ugh. Were off topic. FWIW I have 128K on my truck and its not burning any oil. Can I interest you in some engine flushes? This fixed a whole host of issues for me.

Bull. Every ICE burns/loses some oil, particularly the 4200, without a PCV valve. Might not show up if you do 3000 mile oil changes, though.

Mike

 

[CaptainXL]

Bull. Every ICE burns/loses some oil, particularly the 4200, without a PCV valve. Might not show up if you do 3000 mile oil changes, though.

Mike

Honest. Im pretty accurate checking It used to burn a litttle oil when i got it. Had some stuck rings or something. so over time I have been flushing with kerosene and GM TEC and used BG 44 k. No more smoke out the tail pipe on startup. Even in 20 degree weather. I use Supertech 5w 30.

I know that the 5.3 can develop compression loss andburn some oil so you might want to look into that.

 

[Bartonmd]

Honest. Im pretty accurate checking It used to burn a litttle oil when i got it. Had some stuck rings or something. so over time I have been flushing with kerosene and GM TEC and used BG 44 k. No more smoke out the tail pipe on startup. Even in 20 degree weather. I use Supertech 5w 30.

I know that the 5.3 can develop compression loss andburn some oil so you might want to look into that.

How often do you change oil? Even if it burns a normal amount for this engine, you likely won't notice it in 3000 miles, or some other excessively short OCI. Puff of smoke at start-up is valve seals, typically.

I sincerely hope you're being passive-aggressive and sarcastic, trying to turn it around? Half a quart in ten thousand miles is less oil than probably 95% of GMT360/370 vehicles (or any vehicle, for that matter) burn. They don't develop compression loss, causing the oil burning. The PCV valve that's build into the valve cover gets stuck open, and causes the oil mist to be put into the intake, sucked into the engine, and burnt (see the TSB). A worse condition of the same thing that causes the I6 engine to need the throttle body cleaned every once in a while.

Mike

 

[CaptainXL]

How often do you change oil?

Usually when the GM OLM light illuminates or at least once per year.

Even if it burns a normal amount for this engine, you likely won't notice it in 3000 miles, or some other excessively short OCI. Puff of smoke at start-up is valve seals, typically.

That's what I thought as well. But it no longer has the puff of blue smoke upon startup so idunno.

I sincerely hope you're being passive-aggressive and sarcastic, trying to turn it around? Half a quart in ten thousand miles is less oil than probably 95% of GMT360/370 vehicles (or any vehicle, for that matter) burn.

I drive about 6000 miles a year so I wouldn't know if I burn a half quart of oil every 10,000 miles. Just saying that I haven't seen it. Will keep an eye out.

They don't develop compression loss, causing the oil burning. The PCV valve that's build into the valve cover gets stuck open, and causes the oil mist to be put into the intake, sucked into the engine, and burnt (see the TSB). A worse condition of the same thing that causes the I6 engine to need the throttle body cleaned every once in a while.

That's something else I noticed. Ever since I have done flushes and stuff I have noticed my intake staying clean and the throttle body stays clean. So I guess its not sucking any oil thought the PCV system like when I got it.

 

[Bartonmd]

Oh, that makes sense... This thing, up until the wife's main driver became the '11 Cruze, got 20-30k/year.

Funny story. I read all the stuff about the TB needing cleaned, so at 60k or so, I took the intake off to clean the TB. It was completely "eat off of it" spotless. I was like "Wow, WTF?". Then I did a little more research, and found out that unlike the 4.2's vent, the 5.3 actually has a real PCV system.

Anyway, cheers.

Mike

 

[CaptainXL]

Funny story. I read all the stuff about the TB needing cleaned, so at 60k or so, I took the intake off to clean the TB. It was completely "eat off of it" spotless. I was like "Wow, WTF?".

Yes, my father in law has a 2006 Tahoe with the 5.3 and when I went to clean his throttle body off it was just a little dirty as well.

 

[CaptainXL]

OK now I'm not so sure I have a problem anymore. I took my wife's 2011 Buick Regal on a trip around town and its doing the same thing as my truck. Basically it never fully heats up to 185 like it does in the summer. The gauge reads about 165. Thoughts? Should I be taking this vehicle in for service or just wait until a CEL illuminates? Very frustrating GM.

 

[WarGawd]

How often do you change oil? Even if it burns a normal amount for this engine, you likely won't notice it in 3000 miles, or some other excessively short OCI. Puff of smoke at start-up is valve seals, typically.

I sincerely hope you're being passive-aggressive and sarcastic, trying to turn it around? Half a quart in ten thousand miles is less oil than probably 95% of GMT360/370 vehicles (or any vehicle, for that matter) burn. They don't develop compression loss, causing the oil burning. The PCV valve that's build into the valve cover gets stuck open, and causes the oil mist to be put into the intake, sucked into the engine, and burnt (see the TSB). A worse condition of the same thing that causes the I6 engine to need the throttle body cleaned every once in a while.

Mike

Usually when the GM OLM light illuminates or at least once per year.

That's what I thought as well. But it no longer has the puff of blue smoke upon startup so idunno.

I drive about 6000 miles a year so I wouldn't know if I burn a half quart of oil every 10,000 miles. Just saying that I haven't seen it. Will keep an eye out.

That's something else I noticed. Ever since I have done flushes and stuff I have noticed my intake staying clean and the throttle body stays clean. So I guess its not sucking any oil thought the PCV system like when I got it.

OTOH, if you only put 6k a year on it, I'm surprised it would get noticeably dirty in that period of time anyway. FWIW I've put 20k km (13k miles, essentially 2 years of your driving) on mine in the last 6 months. I had cleaned the TB shortly after purchase, and it was what I would call medium dirty, but not so bad as to have any impact on its operation. So if I get you right, and your TB WAS getting dirty in 6k miles (or less) maybe those flushes really were beneficial in your case, and might not be expected to do much for me (as discussed in some previous thread). FYI, I just changed my oil for the 2nd time since buying it, 1st was change to synthetic with about 25% left on the OLM, then again a week or so ago about 150km past hitting the 0% OLM, and my consumption was almost exactly 1 litre in the 11,500km (7200mi) OCI.

OK now I'm not so sure I have a problem anymore. I took my wife's 2011 Buick Regal on a trip around town and its doing the same thing as my truck. Basically it never fully heats up to 185 like it does in the summer. The gauge reads about 165. Thoughts? Should I be taking this vehicle in for service or just wait until a CEL illuminates? Very frustrating GM.

I'll toss some of my personal experience out there for you to chew on...may bear some relationship to your issue.

First, it does sound to me like the 'stat is stuck. I had a similar issue, and as Fall cooler temperature approached I saw the truck having more frequent difficulty maintaining temp. Then I changed 'stat and sensor which immediately resolved the problem and temps always came up to normal and stayed dead steady during operation. Then I went out in -18 deg temps to do some long exposure astrophotography during the Geminid shower in Dec. I left the vehicle idle the whole time to keep warm, and I noticed that with the fan on high and dual climate controls set at max, non-recirc, rear heat off, the engine temp would slowly (span of about 4 hrs) fall off to way below normal operating temps. I have had this occur a couple more times in similar circumstances, and I have concluded that the cabin heater is capable of pulling enough heat out of an idling engine to cool it off by itself, when ambient temps are very low. And the t-stat would be closed fully in this situation.

So what I am saying is, while you may have a stuck stat on your truck, the Regal may be getting sufficient cooling from just the cabin heater fan on high under light/short driving conditions...make sense?

 

[CaptainXL]

So its not just me. The only time the engine never gets to temp is when the heater fan is on full blast. This is characteristic of both vehicles. So I am not sure I really have a problem anymore. Going to check radiator again to see if there is any coolant flow before reaching temp. Its been 0 F here lately and I have noticed this behavior more.

I know some on here dont think putting a grill cover on is a good idea but now I can see why they are used up in Canada and such.

 

[Robbabob]

Its been 0 F here lately

I guess I didn't ask you properly last week, to increase the temp during my visit from TN. Yikes, 1° yesterday morning and 4° today; yeah, I remember now what the F stands for!

 

[The_Roadie]

...the cabin heater is capable of pulling enough heat out of an idling engine to cool it off by itself, when ambient temps are very low. ...

Exactly the reason if you're overheating in high summer temps, you can turn off the AC, open the windows, and put the heater on full to assist the radiator.

 

[Bartonmd]

So its not just me. The only time the engine never gets to temp is when the heater fan is on full blast. This is characteristic of both vehicles. So I am not sure I really have a problem anymore. Going to check radiator again to see if there is any coolant flow before reaching temp. Its been 0 F here lately and I have noticed this behavior more.

I know some on here dont think putting a grill cover on is a good idea but now I can see why they are used up in Canada and such.

Depends on what loads the engine is seeing. Just normal country driving, or interstate, or state highway, with the fan on high in the 5F temps we've had lately, my TB gets up to full temp, no problem, with the heater on high/hot. However, as said, if you're idling a lot, or maybe driving in congested city traffic below 0F or something, I could see it not completely warming up. However, if you're putting any real load on the engine, highway for instance, and it's still not heating up, your stat isn't closing completely. Even with outside air temp coolant in the radiator (just got on the highway with a cold-ish engine), if you're on the highway, that's quite a bit of load; and if the stat is really closing completely, it should have no problem getting to operating temperature, no matter what you're doing to the HVAC.

Mike

 

[CaptainXL]

Just got All my parts in and now I am having doubts about installing them.

I could use some advice on a surefire way to determining if the thermostat is stuck open. No matter what temp it is outside or what load the engine is under. Would checking the radiator to see if there is coolant flow be sufficient?

 

[meerschm]

Mine warmed right up on the way to work this morning. it was around 15f. (surface street drive, never over 35 MPH, and pretty long lights around here)

the only way to tell is to remove the thermostat, and give it a close look. you can monkey with it if you want, but I would just change it out.

if you want, you can put it in a pan of water on the stove and warm it up and watch. (with a thermostat in the water if you like)

I suspect there may be something interfering. could be a loose/extra gasket, or some other item, or just be defective from the start. you will not know till you take it out.

it does sound to me like there is too much coolant getting past when the thermostat should be closed.

Edit: with you having an XL and perhaps rear heater with many more feet of heater hose/lines, you may have more thermal load than my swb. you could look at wargawd's logs to compare your performance.

 

[WarGawd]

Exactly the reason if you're overheating in high summer temps, you can turn off the AC, open the windows, and put the heater on full to assist the radiator.

Yep - I've seen rally car drivers do this, sweating their a$$es off in their suits just to try and get enough extra cooling to keep going.

FWIW, I also had to do an hours worth of datalogging this morning in -28 degC temps, and I played with a variety of fan speed/recirc/cabin temp settings throughout - the effects are directly observable in the logs if anyone is interested.

 

[WarGawd]

Just got All my parts in and now I am having doubts about installing them.

I could use some advice on a surefire way to determining if the thermostat is stuck open. No matter what temp it is outside or what load the engine is under. Would checking the radiator to see if there is coolant flow be sufficient?

Barton pretty much said the same as I'm about to. This morning I had to take a trip up the highway, about 1/2 hr. Idled a while to get some heat and set up my laptop for logging. Despite ~15minutes idling temp never came up more than about halfway to normal (guage indication). As soon as I started driving in town to get to the highway, I could watch the real time temp (scanner) climb quite quickly. Small town, only took me 5 min to get to the highway access and I was almost normal by then. On highway temps hit 201F and stayed solid within a couple degrees of that.

Pulled in to the courthouse to pay a fine, parked and let it idle with scanner running. In less than 15 minutes, the temp had dropped to 154F and seemed to be levelling off there. I switched on recirc, let it idle another 5 min and could see the resulting temp increase. Later on I parked at a pawn shop, idled with cabin fan off for 10 min or so, temp didnt drop much at all. With a new t-stat that I know closes fully, I am considering this to be normal behavior.

So summary is, ANY load above bare minimum should get you up to temp fairly quickly, if not stat is stuck. And if it's only stuck open a small amount, you might even give it an assist and buy a bit of time to replace in more favorable conditions by turning on recirc, and turning fan speed down a notch or two. Or use a Canadian grill cover

 

[CaptainXL]

Tested the new one...

The thermostat doesn't start to open until about 198F of so. I blew into the outlet end of the housing while watching the water temp go up from 140F to 215F. I blew through it every 5 degrees so I could catch it in the act. Interestingly, I was hoping for it to start opening as low as 185F but that wasn't the case. Perhaps if there was some pressure behing the spring then it would open more easily. So to be fair lets say that it more than likely opens somewhere between 190 and 198F

I noticed that there appears to be a point when the thermostat is opening where the bulb rubs against the guide on the spring retainer (pictured below). Weather this is normal or not I don't know.

Now that I know it doesn't open or even start to open untill 198F I can go investigate the thermostat in my truck one more time to be sure.

The thermostat unpacked:

View attachment 25996

Thermostat fully opened at 212F. Man that's not that far. And notice the oring/seal ready to come out and fall inbetween the thermostat

View attachment 25997

Possible issue? Rubbing spring retainer. Note offcenter bulb.

View attachment 25998

You can definitely replace just the thermostat if they sell them. Just take it apart!

View attachment 25999

 

[CaptainXL]

First, it does sound to me like the 'stat is stuck. So what I am saying is, while you may have a stuck stat on your truck, the Regal may be getting sufficient cooling from just the cabin heater fan on high under light/short driving conditions...make sense?

Well that definitely makes sense and it makes even more sense to me because my recirculate actuator is broken and sucking in cold air all the time. The next time I go out tonight to start my truck from a deep cold soak we will see. i am suspicious that the thermostat is just acting normal. It could have been the case that the coolant in the radiator was still hot from my previous drive the last test I did. But that was about 6 hours before and it was in the 30's at the time IIRC. So we will see. Gonna double check.

 

[Jon A]

I recommend you do not install that thermostat. While it should solve your problems of running cool in the winter by closing completely, you're likely to have overheating problems in the summer. By 212 degrees it should be open three times that far. I believe the bulb rubbing on the housing is preventing it from opening as far as it should. Replacing these things is too much a PITA to do it twice.

I recommend instead you get a Motorad: Motorad 413-192 Thermostat : Amazon.com : Automotive . Quality. Made in Germany. It'll work. Test it next to this one and make your choice.

 

[CaptainXL]

I recommend you do not install that thermostat. By 212 degrees it should be open three times that far.

Well that's simple enough to test. I can just take the thermostat apart as in my last picture and see if the pintle actually extends further than before. I don't think it's really getting hung up on the spring retainer...just rubbing it.

Edit: Ok, I think I know whats going on here. The thermostat definitely opens alot more if the spring isn't holding it back. That is when the thermostat is removed and dropped into water by itself. It actually pops when the water goes boiling.

Now of course the spring pressure must be figured into the equation when it's all put back together with the housing. So naturally the spring must overcome the pressure of the water pump to retract the thermostat when the coolant gets cooler. So all in all this appears to be normal. Funny that I'm being overly cautious about all of this. Better to be safe than sorry I guess. Let me see if I can find another stat in a store around here and I can confirm my findings.

 

[CaptainXL]

I recommend you do not install that thermostat.

I would agree if it wasn't for one observation I am seeing. The coolant is getting warm in the radiator from the moment I start up the truck.

This is either engine heat escaping/rising through the top housing leading to the radiator or I have a stuck open thermostat.

Can someone who has a known good thermostat please run their truck until the temp gauge gets halfway hot and then stop their engine and open the radiator cap to see if it is warm? I am trying to see if the heat is coming from the top radiator hose or not. It's impossible for me to see coolant movement in the radiator unless I drain the radiator half way down. I just might end up doing that if needed.

 

[Bartonmd]

I would agree if it wasn't for one observation I am seeing. The coolant is getting warm in the radiator from the moment I start up the truck.

This is either engine heat escaping/rising through the top housing leading to the radiator or I have a stuck open thermostat.

Can someone who has a known good thermostat please run their truck until the temp gauge gets halfway hot and then stop their engine and open the radiator cap to see if it is warm? I am trying to see if the heat is coming from the top radiator hose or not. It's impossible for me to see coolant movement in the radiator unless I drain the radiator half way down. I just might end up doing that if needed.

Do what?!?! By that time, there should be some pressure in the system, so you're asking people to risk getting hot coolant on themselves, to see something that can't be seen if the coolant is at proper height (just below the cap), anyway?

Mike

 

[CaptainXL]

Do what?!?! By that time, there should be some pressure in the system, so you're asking people to risk getting hot coolant on themselves, to see something that can't be seen if the coolant is at proper height (just below the cap), anyway?

Mike

Yes there is pressure in the system but the coolant should not be hot, it should be cold.

When opened my radiator cap when the needle on the gauge was about halfway up the coolant was warm, not hot. There was a little pressure involved but nothing close to boiling steam escaping. So I would say it's a relatively safe test.

 

[WarGawd]

Alternatively, just start the truck from cold with the cap off, no pressure will build to pose any danger. Even with the cap on it wouldn't happen in the time period Capn is proposing. I'm comfortable enough doing this, removed caps under pressure many times - just check hose pressure (hand squish test) to get an idea first. Anyway, despite any limitation on ability to see, I have a thermocouple on a 4-foot wire calibrated for use with my DMM - it'll be relatively easy for me to see at what point the DMM starts to show temp change in rad vs guage indication on dash.

I'll try to tackle this in the morning, I have other reasons to be under the hood.

 

[Bartonmd]

Yes there is pressure in the system but the coolant should not be hot, it should be cold.

When opened my radiator cap when the needle on the gauge was about halfway up the coolant was warm, not hot. There was a little pressure involved but nothing close to boiling steam escaping. So I would say it's a relatively safe test.

What you said was "gets halfway hot" so I see somebody waiting until their gauge gets to the halfway point (you said halfway hot, not halfway warmed up or halfway to operating temperature, and "hot" is all the way to the right side of the gauge, after all), not knowing to slowly release pressure, and opening it just like you told them to do.

The other part of my post was that if somebody has a full radiator, opening the cap won't tell them anything that feeling the hose or top radiator tank won't tell them.

On a car forum, when openly asking for anybody to do something to their vehicle (especially something that sounds simple), remember that there are a lot more helpful people on forums than there are people who know how to safely work on cars.

Mike

 

[WarGawd]

Test complete. Ambient temps were 21F / -6C and that was matched by rad fluid temp after overnite cold soak. Cap removed, thermocouple inserted in rad. Started truck, snapped pics along the way. Bottom line is that the rad temp never began to change in the slightest until the dash guage indication was very near to normal operating position. My dash guage is accurate, I calibrated it after replacing the stepper motors, normal operating point is right side of needle jussssst touching the left side of the 100C gauge mark. normal temp ~201F = 94C, t-stat was rated at 92C

Pics attached show the point where the rad started to show first temp change vs dash guage indication, and given your description I'd say your t-stat is "bad". That may be a matter of degree, and it may be adequate for a while till weather improves if you wanna DIY, and you can help it out by keeping fan speed a notch or 2 off max.

View attachment 26072

View attachment 26073

View attachment 26074

Cheers

 

[Jon A]

I would agree if it wasn't for one observation I am seeing. The coolant is getting warm in the radiator from the moment I start up the truck.

Two different problems. Yes, I do believe your current thermostat is sticking open which is what is causing the problems you are encountering now. Replacing it should fix that problem.

However, I'm pointing out another problem with your new thermostat. This is what a properly functioning open thermostat looks like:

Compared with your new one:

If your new thermostat does not look like that at 212 degrees, it is no good. Regardless if it is brand new or not. It will cause a completely different problem--it will limit the effectiveness of your cooling system. In the summer when it's hot, if you work the engine hard the cooling system won't be able to keep up with as much heat production as it should be able to due to the limited flow rate of the coolant.

I am not pleased with the quality of the OEM thermostats in these vehicles as way more people seem to have problems with them than they should. Whether it's lack of quality or poor design (you can see the Motorad above has a softer, more progressive spring as one obvious design difference) I don't know. I do know, if you want your cooling system to work worth a darn, you need a thermostat that opens more than a crack.

 

[CaptainXL]

Thats great info guys. Jon that demo you did is great. I am going to boil my new tstat one more time fully assembled. I could only get it to pop fully when removed from the housing. Jon what brand is that? Motorad?

Wargawd. Thats was a cool demo as well. Thanks for clarifying. Did you notice the upper radiator hose having any warm coolant escaping towards the radiator during that test? I dont have a thermocouple so cant replicate your findings exactly. So just to clarify you tested the temp of the coolant at the top and bottom of radiator?

 

[Jon A]

Jon what brand is that? Motorad?

Yes, a Motorad. They are available in some local parts stores but easy to find online as shown above. For reference, it opened .3"-.35" (not perfectly evenly) which is pretty typical for an automotive thermostat.

As I said, replacing them is a bitch. I wouldn't go through the hassle only to put a sub-par one in there.

 

[CaptainXL]

Tested the made in mexico ACDelco again. Seems to not work well at all. Gonna order a Motorad 413-192. Amazon is also sending me a replacement ACDelco tstat. I just want to see if they really are bad. Perhaps I just got a dud.