I'm cool, do you think I'm cool? I think I'm cool. (question on being cool)

[Hink]

Not sure how good IR guns are today but different surfaces will have different emissivity. Not sure I would argue 5-10 degree difference in IR gun readings depending on different surface emissivity

Right, I measured it at various places, temp sender at radiator, top of radiator on both sides, head at temp sender. I settled on the front of the drivers head on the brass sender itself because I figured that it was the closest to where it was actually picking up the signal to send to the gauge.

A 195F stat might open at 194-196? in a switch like fashion

While working at NAPA for many years, many years ago they had (and still do, I believe) a line of thermostats called the superstat. They were a progressively opening stat where the lower line would be an only open/only closed type. I don't think the superstat was anything special, I think factory stats are all progressive but the lower line were just crappier.

The thermostat is not suppose to influence or control the max temperature at all.

I'm just a shade tree mechanic, not an automotive engineer but the way I understood it is that it shouldn't control, but it will influence. By starting to open 15* sooner (along with the fan clutch engaging 15* sooner), the 180* stat will allow the radiator to start shedding heat sooner. If I'm towing and don't want to go above 210* and I hit the 195ish range for the stock stat, I only have that 15* swing before I'm in trouble. You'll roll through that 15* real dang fast when you're pouring that much more fuel to it. Starting the cooling cycle (stat open, fan clutch engaged) stops the runaway heat (well, to a point anyway).

 

[schiker]

I am not always the best to type things out and it may take a back and forth or another's explanation. I did some application testing with engine size and radiator sizing vs load and it can be described as a heat balance.

Different factors can apply for cyclic loading vs continuous loading ie rolling hills vs long grade or wind drag and head wind.

Heat dissipation increases with increase in difference in temperature so a radiator at avg 190F will shed more heat than one at 175F. So there might be a time lag while increasing coolant temp but if radiator is already hot its shedding more heat. When the radiator is small and or air flow is inadequate the stat temp may just flow earlier not control top temperature. For a cycling load it may a short time delay when heat load is added. Its still going to overheat which ever stat you have low or high temp given time at load. Actually low temp is less efficient and power is down etc so there are disadvantages as well.

Maybe we should stick to one scenario at a time. The difference in a 180F vs 195F won't stop overheating because if the heat shed is not balanced with heat load temperature will rise over time and overheat (one just flows earlier than other).

The only reason I run 180F is to reduce underhood temps in summer with AC on just daily driving. Now that I have bumper mounted FSD next time I will probably go with 195F stat for efficiency.

 

[THEFERMANATOR]

The only thing going to a lower temp stat does is make it take longer to get up to the overheating temp. A 190 stat is mostly open by 200-205, so anything more than that is what it is going to run at. Once the stat is open, it's open, and the system is doing all it can do. So if it continues to climb past teh 205 mark with a 190 stat, it will do the same with a 180 stat, just taking longer to do it since it started opening sooner. Also keep in mind those bigger temp swings under load is harmfull to metal. Many don't like a 190 stat with a 210 fan kick in as they feel this is pushing the limits, and trying to run to tight of a window, but this tight window actually reduces metal fatigue, and cooling system shock loading. And one of the WORST things you can do is to remove the stat in a system with a bypass that needs to be blocked. Many a 7.3L powerstroke has been lost by people doing just this. Or the other way was by people wanting them to run cooler, so they put in an international stat(180), but they didn't realize the international stat was a different length, and never fully blocked the bypass, which in turn lead to lack of coolant flow to the back of the block, and boom went the 7.3L powerstroke.

 

[Will L.]

Yes I agree, it takes longer to get up to over heating temp. However, if your engine can produce more btu than your radiator can handle it can make a difference in temporary heavy loads. Hink's radiator is shedding all the btu he is throwing at it, evident by thermostat temp to operating temp scale between changes.

Take my hummer, on flat ground I can run near full throttle 90 mph all day long and not get over 200. If I climb freeway hills (that slow loaded semis down to 50-55 mph idk grade) for 2 minutes I can not maintain 50 mph without hitting 220 or more. That's with a 195 stat. I go to a 180 stat and I can pull the same hill at 60 and never hit 215. My normal operating temperature is 185 vs 195.

My radiator can not handle the btu I put out under load. But the tipping point into overheating is held further out by starting the cooling earlier. That 10 degree difference is huge. When it is below 70 degrees and humidity is over 30% I can do 80 up the hill and never hit 200 with egt running the same because the radiator efficiency is up shedding the btu.

So if you put in a thermostat that closes at 220 and opens at 240 is your engine going to run at 195? No. While the engine has its thermodynamic equilibrium with its radiator, you can push it up or down the scale. By retaining heat in the engine with too high a thermostat, you can get it too low with too low of a thermostat if, like Hink, you have too large (by btu for demand) of a radiator.

So is taking longer to get to overheating temp good? If it takes you 10 minutes to build the heat until overheat, and it's a 10 minute grade, 5 degrees earlier can make all the difference. So IMO it depends on your situation whether or not to do it. Hink should probably swap his fan clutch to not kick in till 20 degrees more.

Now, don't take this next part personal, I know your relaying what you've been taught, but this one is like the teachers explaining the earth is flat back in the day- just wrong info from your instructors.

On the metal fatigue, engineers in automotive area argue this back and forth, but structural engineer /metulurgists working with high heat metals all know the truth.
I worked with metals of all types and grades that have to cycle from 150f to 2100f and back down in a matter of 20 minutes, then the cycle extends peak temperature time for up to 6 days at a time before cooling to ambient under refrigerant to drop from 2100f to -300 in 45 minutes.

It is done with cast iron 1/4" thick. The same vessels have been following this cycle since the 50s. They are 0 pressure vessels. I had to play with inconel running at 3500f in the titanium production world. It looses heat so fast it goes from full heat where you can see through it watching the liquid splash cool to 400 in minutes before its poured out. The high pressure stainless steel vessels do the same type of temp swings but in nearly a thousand of psi. Decades of running. We deal with metal fatigue. X-ray gear all the time.

The automotive world theorizing about metal fatigue from rapid temperature swing of less than 100 degrees is just silly to guys like me that watch 18" stainless steel shafts 45' long grow to full length in 20 minutes.

My Dad was an aircraft mechanic / engineer for unky Sam most his life. Worked some things like u2, blackbird, space shuttles. He was the lead instructor for the USAF on failure diagnostics for decades. So yes, I understand a little of it from him. One of my really good friends dad is the head of nuclear inspection team. He has inspected every nuke device of the US power related. He knows a little about fatigue also. This subject came up with him as well in hotrod automotive discussion. He just laughed...shook his head and walked away, laughing.

If temperatures from <100 degree swings was that bad, even if it is in 1 second, how does the same engine block and heads get used season after season running top fuel. That heat and pressure change is amazingly worse, yet the tears-downs nor fracture inspections don't show the overload, rough,smooth fatigue regions. Every blown engine I've seen shows stress fracture.

Take an old head and the biggest rose bud you have. Go 450 to dropped In water and see how long it takes to get expansion fracture- you'll get an idea. Then do it with a old skillet handle, say, 200 cycles and once cooled the last time see if you can bend or break it without the pull fracture indicators. Won't happen. It will harden raising the hardness, but no fatigue.

Can you harden your cast parts till the are more brittle and fracture easier? Yes, but the pressure required will blow the valve through your hood when your about half way there.

Too many people reading about the amazingly thin aircraft skin and wondering, can that effect thier engine. Find 1 engine part with fatigue fracture signature and test metallurgy.

I have several myths out there that really get under my craw, can anybody guess one of them?

 

[Hink]

Yes I agree, it takes longer to get up to over heating temp. However, if your engine can produce more btu than your radiator can handle it can make a difference in temporary heavy loads. Hink's radiator is shedding all the btu he is throwing at it, evident by thermostat temp to operating temp scale between changes.

Take my hummer, on flat ground I can run near full throttle 90 mph all day long and not get over 200. If I climb freeway hills (that slow loaded semis down to 50-55 mph idk grade) for 2 minutes I can not maintain 50 mph without hitting 220 or more. That's with a 195 stat. I go to a 180 stat and I can pull the same hill at 60 and never hit 215. My normal operating temperature is 185 vs 195.

My radiator can not handle the btu I put out under load. But the tipping point into overheating is held further out by starting the cooling earlier. That 10 degree difference is huge. When it is below 70 degrees and humidity is over 30% I can do 80 up the hill and never hit 200 with egt running the same because the radiator efficiency is up shedding the btu.

So if you put in a thermostat that closes at 220 and opens at 240 is your engine going to run at 195? No. While the engine has its thermodynamic equilibrium with its radiator, you can push it up or down the scale. By retaining heat in the engine with too high a thermostat, you can get it too low with too low of a thermostat if, like Hink, you have too large (by btu for demand) of a radiator.

So is taking longer to get to overheating temp good? If it takes you 10 minutes to build the heat until overheat, and it's a 10 minute grade, 5 degrees earlier can make all the difference. So IMO it depends on your situation whether or not to do it. Hink should probably swap his fan clutch to not kick in till 20 degrees more.

Now, don't take this next part personal, I know your relaying what you've been taught, but this one is like the teachers explaining the earth is flat back in the day- just wrong info from your instructors.

On the metal fatigue, engineers in automotive area argue this back and forth, but structural engineer /metulurgists working with high heat metals all know the truth.
I worked with metals of all types and grades that have to cycle from 150f to 2100f and back down in a matter of 20 minutes, then the cycle extends peak temperature time for up to 6 days at a time before cooling to ambient under refrigerant to drop from 2100f to -300 in 45 minutes.

It is done with cast iron 1/4" thick. The same vessels have been following this cycle since the 50s. They are 0 pressure vessels. I had to play with inconel running at 3500f in the titanium production world. It looses heat so fast it goes from full heat where you can see through it watching the liquid splash cool to 400 in minutes before its poured out. The high pressure stainless steel vessels do the same type of temp swings but in nearly a thousand of psi. Decades of running. We deal with metal fatigue. X-ray gear all the time.

The automotive world theorizing about metal fatigue from rapid temperature swing of less than 100 degrees is just silly to guys like me that watch 18" stainless steel shafts 45' long grow to full length in 20 minutes.

My Dad was an aircraft mechanic / engineer for unky Sam most his life. Worked some things like u2, blackbird, space shuttles. He was the lead instructor for the USAF on failure diagnostics for decades. So yes, I understand a little of it from him. One of my really good friends dad is the head of nuclear inspection team. He has inspected every nuke device of the US power related. He knows a little about fatigue also. This subject came up with him as well in hotrod automotive discussion. He just laughed...shook his head and walked away, laughing.

If temperatures from <100 degree swings was that bad, even if it is in 1 second, how does the same engine block and heads get used season after season running top fuel. That heat and pressure change is amazingly worse, yet the tears-downs nor fracture inspections don't show the overload, rough,smooth fatigue regions. Every blown engine I've seen shows stress fracture.

Take an old head and the biggest rose bud you have. Go 450 to dropped In water and see how long it takes to get expansion fracture- you'll get an idea. Then do it with a old skillet handle, say, 200 cycles and once cooled the last time see if you can bend or break it without the pull fracture indicators. Won't happen. It will harden raising the hardness, but no fatigue.

Can you harden your cast parts till the are more brittle and fracture easier? Yes, but the pressure required will blow the valve through your hood when your about half way there.

Too many people reading about the amazingly thin aircraft skin and wondering, can that effect thier engine. Find 1 engine part with fatigue fracture signature and test metallurgy.

I have several myths out there that really get under my craw, can anybody guess one of them?

And BOOM goes the dynamite.

 

[THEFERMANATOR]

Not to argue, but I'll use some examples I have personnally seen. I used to work for JEEP and did quite a bit on the side with the straight 6's. I've personnally seen plugged heater cores cause temp spikes of 220 or so, and when the stat finally opens, that 60 degree or so coolant hits #1 cylinder(the JEEP straight 6 puts the water pump directly in front of #1 cylinder in the block, it gets hit with incoming coolant directly) and cracks the cylinder wall. One of these engines was a 14k mile engine, so heat cycling over time wasnt really an issue there. And I hada cousin who had one overheating, so he added some water from a jug he had in the back. The engine was still running fine, as soon as the water hit, it went to misfiring, cracked the cylinder wall in 3 places right behind the pump. And I've seen many more just like these.

So from personnal experience, I prefer a narrow temp range to run in. It's one of the things I dislike about my DURAMAX. I'm not fond of the stats starting to open at 180, but waiting until 212 just to block the bypass, and 230 before full open and the clutch engages(my hayden comes in about 220 for the most part).

 

[Will L.]

I never take anything you say as an argument, and I hope you know I never intend argument either. I think you just have a little misunderstanding of what's happening because it's not really taught in the automotive world. I learned about fracture diagnostic from my dad as a teenager, but didn't apply it to much until I started working around the fuel industry.

What you're describing is thermal shock, and the rapid temperature change is what can cause it. That's what I was describing with the torch and water scenario. If an object is a high heat and one area gets cold very rapidly while the rest stays hot, the cold part will shrink while the hot area stays expanded. That is what causes the fracture (or crack).

This is very different from the entire system heating up and cooling down as a unit. In fact a wider temperature range of movement at a slower pace is easier on cast components than rapid small changes. That's why welding cast iron you have to preheat and post heat. So starting the cooling process sooner rather than later would cause both less thermal shock and less metal fatigue.

 

[Hink]

Ok, so I put the 180* stat and a thermometer in water and turned on the heat today.
The stat was surprisingly accurate. It began to open at about 184* or so. At least that's when I could actually see it a bit open. It's likely that it started actuating right at the 180* point. On cool-down it had closed by about 178*, so operates very much in the 180* range.

Seeing this actually makes this situation more confusing though. Referring back to my request for verification on my understanding on the dynamics of the cooling system in post #22, there should have been no change at all between the two thermostats since they weren't even near their operating range of 180* or 195*.
When the truck was running an operating temp of 135*, the stat was closed. Now running at 165*, the stat is still closed so why the 30* difference? The radiator is likely cooling well, but it hasn't even been introduced to the cooling cycle at this point, right?
Wierd.

Again, (I have to drop clear back to basics here because it's likely that I have misunderstood even the basics all these years : )>) my understanding is water pump cycles coolant through the engine, at operating range of thermostat (mine being 180*), thermostat begins to open to allow coolant to flow through radiator to begin shedding more heat while stat fluctuates between open and closed to keep coolant within operating range determined by the thermostat, again mine being 180*. What am I missing? Help me oh wise ones!

Now that I've tested it, I'm going to put the 180* back in and see if it reacts the same and also verify the operating range of the 195* stat.

 

[Will L.]

Thermostat closed, the bypass is open. That water circulating is getting cooled in the radiator. Although you're not reading 180 on your gauge, A little amount coolant getting to the thermostat is heating enough to cause it's open slightly.

With the higher tstat, it's holding back all the coolant that was sneaking by the stat at 180 until that coolant gets to 195. Then it cracks open the stat joining the bypassed coolant to get fooled off.

If you pinch off the bypass hose, you'll see your temps climb. This is a perfect example of the difference of a bypass design vs non bypass crossover (like my old single stat crossover) operating at temps below and up to tstat temp.

Your radiator/ heater core is just kicking butt. Take it out of the cold, 75% humidity and to somewhere hot and dry to watch it climb.

 

[Hink]

Yeah, I forgot the bypass in my tirade there... but that's still crazy. It's not the hot and dry like you say but it has been in the 70s so I'm looking forward to seeing how she does this summer. I may just be eating my words so I probly better shut the hell up now.

Sorry we couldn't have found the key to coolness for you here.

 

[THEFERMANATOR]

The bypass goes back to the water pump, so no coolant circulates through the radiator from there. The heater core does circulate back to the radiator, but only on the cold side to help keep the trans cooler in constant circulation. One thing I have seen cause cold running issues with a functioning t-stat is the wrong water pump. If the impeller is backwards, it will make one run super cool. Otherwise your gauge is just that far off(which is VERY believeable on those old clusters).

 

[THEFERMANATOR]

I went and relooked at your 1st pic, that is about 165 or so on the gauge. That middle hashmark is 180 degrees just FYI, not 155 like you would think. And did you say you have replaced the sending unit for the gauge? If so theres your other issue. I have been through 4 in the last couple of months, and I have YET to find one that reads correct. The ohms on them is dead on for each temp to ohm reading, but the thermistor is of to low of a conductor design to make the gauge read accurately. My DURAMAX uses a 180 stat for the low temp stat, and that is about where my gauge read with an aftermarket sender installed when the engine was 180. The issue is the truck clusters draw right at 1.83 watts through the sender circuit to make the gauge work, and the new senders are calibrated for car gauges that draw about 1-1.2 watts.

 

[Hink]

Dang it Ferm, stop talking sense!

Except it's the same pump that was running at 175* on the old engine. But he's right Will, that the bypass does run to the pump. So what the heck is the bypass for then?

That middle hashmark is 180 degrees just FYI, not 155 like you would think.

You're kidding me, the gauge isn't linear? So do you know how much each smaller hash mark is? Good Lord, they have to make these things difficult. So basically, with a borked sender, an inaccurate gauge and no way to accurately tell temp with an ir gun, you're pretty much just ballparking the whole situation.

Cool.

 

[NVW]

AFAIK the bypass aids in engine warm up, recirculating heated coolant. When the Tstat closes it the flow goes to the rad.

 

[THEFERMANATOR]

It allows the coolant to circulate through the engine to keep coolant flowing(stop hot spots during warmup), stop the cooling system pressure from holding the stat closed, and to also help regulate flow through the radiator via the bypass blocker on the stat if it has one(also helps to prevent shock to the block by mixxing hot coolant with the cold so when the stat 1st opens, the hot block doesn't get hit with cold coolant).

And no, the gauge is not linear. The bottom mark is 100(even though 95+ diesels start at 160, it is actually 100), the next is 180(verified 3 different clusters that this mark corresponds to 180 degrees for resistance), then 210 is straight up, and it's pretty linear from there over with roughly 235 at the next hash and 260 at the top. The sender is a common issue, and it seems oem's are now the worst. I have 1 sender that works, and it's the origanal 95 one that came in it new. I've tried numerous others(for another project), and have yet to find one that works. The ohms on them is dead on at each temp point, but the backprobed voltage will be to high from the thermistor not being up to the current load.

As to knowing the temp, I used my scanner and made a reference as to what each temp actually is on my gauge using the temp reading from the ECM's reading. Doesn't do the op much good though since his doesn'thave an ECM to check against.

 

[Hink]

Excellent! Thanks for that explanation Ferm.

 

[Will L.]

I'm blaming old age. It's not why I was wrong, I'm just blaming it. But my theory was just stupid thinking about it now on it. That's why I like Ferm, he doesn't tell me I'm being dumb, he shows proof and let's me figure out how far off my thought was!

How much coolant flows brought the bleed hole in the thermostat? Could that be enough to keep it down? Did the 180 have the rubber gasket on it? I'm guessing you check for leaking seal around the thermostat like Ferm mentioned,maybe that slipping past the thermostat?

I know the modified speedway motors thermostats are just drilled to allow more flow through prior to opening. Simple trick worked in gasser hotrods for years fighting desert heat. I tried one on my Hummer, it helped about 5* worth was all, but that was using unbalanced water pump. Never tried it with the corrected waterpump.

So the 180 tstat made it run 165, and the 195 made it run 185ish?

And WOW- I knew the dash gauge wasn't to scale but I never realized it was that far out! If the single pin sensor is that bad, how far out is the dual sensor that sends signal to the komputer and scanner, or is it still being built quality? I wonder what the "go to" brand sensor is. Does AC Delco produce the GM sensor that's bad? If so they used to be pretty good about looking at bad parts to fix quality control in the past. If you have new ones that far out, call and they should email you a prepaid shipping label to send to their QC folks.

In the end a high quality aftermarket gauge has always been my preference. I'm not sure who made the gauge in my Hummer (Iirc VDO) but I recheck it every few years compared to the Waekon pressure gauge unit, so it's good. Sucks for the sensor when it finally needs a new one, what to get?

 

[THEFERMANATOR]

3 of those 4 bad ones I've had, have been the 3 wire coolant temp sensor with the 2 wires to the ECM, and 1 to the gauge. I looked on AMAZON though, and people have the same compalints with the replacement 1 wire senders from GM, and most all the rest. Peopel have had better luck with the aftermarket ones from the parts stores than OEM as of late(my aftermarket 3 wire was the WORST of the lot though). I have a feeling now that he knows that hash mark is 180, not 155, the temp probably makes more sense to him. I know with the 3 wire sender in mine, it runs about 1-1.5 marks below the 180 hash mark at 180-182 according to the CTS from the ECM feed. I've read online, and SEVERAL people have complained about this with the new sender's from all the manufacturers. Just more of this made in china crap to deal with.

 

[Hink]

Yeah, I lot of things makes more sense now but there are still two things that don't...

1 - In my first picture, It's not running anywhere near 180* with the 180* stat in. And that's going 70mph down the freeway. So the stat hadn't even opened then. Weird, but it leads to the next thing...

2 - If the 180* stat wasn't even opened at that point, why did the 190* stat change the running temp at all?

So the 180 tstat made it run 165, and the 195 made it run 185ish?

Yeah, the 195* stat ran about 185* or so it seemed. So why is the engine getting to operating temp with the 195 but not the 180? It's the same gauge and sender, so even establishing that they are likely off, it doesn't account for that.

As for the rubber gasket, it took me a while to recall but I remembered that some applications had a rubber gasket and some had a paper one. The '93 6.5 uses a paper gasket and I use a new one every time and have no leaks (or no reason to expect any internally), so that isn't likely an issue.

I'll try to get the 180* stat back in tomorrow and do the same stove test on the 190* just to verify everything but it still doesn't explain the cool running engine on the 180* stat that we now know opens in the right temp range.

One things for sure, if this is my biggest problem after all the work I've done on the truck in the last year, I'll be perfectly fine with that!

 

[ak diesel driver]

The ones that use the rubber also use it to seal the thermostat from leaking coolant past it. So even tho its not leaking externally it might be letting coolant past internally simulating a stuck open stat.