You can’t trust thermostat ratings

[RustyRatRod]

Gotta disagree with that. Everything I have ever seen or read stated that the temp on a thermostat was when it started opening. @RustyRatRod was an Oriellys manager for years, and I agree with him.

Oh GAWD well there's the gauntlet. LMMFAO. What a stretch.

But seriously, that's all I've ever seen @MOPAROFFICIAL as well was that the thermostat just begins to open at the rated temperature. It's fully open at "a little" higher temperature.

Oreilly. LOL That's a hoot.

 

[RustyRatRod]

Thank you for actually doing the footwork most people either just believe or deny it and never tested themselves.

They start opening before the temp rating at which they are fully open at.

People think they just POP open..lol.. yeah.. a big pressure spike is what you want...not.

They have to because it's a curve based on how the thermostat is made. They don't just "pop" open at *** temperature. lol

 

[hotrod swinger]

I definitely made a big difference to my operating temperature, that much is clear.

 

[hotrod swinger]

I wonder if the laser thermometer could be off also? Could be a combination of the thermostat opening a little early and the thermometer reading low.

Double verified with laser thermometer and mechanical water gauge next to thermostat. Mechanical water gauge is always approximately 3-5 higher than the laser.

 

[MOPAROFFICIAL]

They have to because it's a curve based on how the thermostat is made. They don't just "pop" open at *** temperature. lol

Then it must be a "so n so is my forum hero so I'm listening him" deal... because I've said this..and on this site for decades and everytime its brought up it's like I have to re convince some folks. And yeah the orielys manager part was classic..you know you're a friend when I hold back from that kind of opportunity
Even motortrend explains it wrong.
There is a bunch of confusion out there...hope they all figure it out and feel like schmucks for telling me I'm wrong...when I'm trying to help.

 

[RustyRatRod]

Then it must be a "so n so is my forum hero so I'm listening him" deal... because I've said this..and on this site for decades and everytime its brought up it's like I have to re convince some folks. And yeah the orielys manager part was classic..you know you're a friend when I hold back from that kind of opportunity
Even motortrend explains it wrong.
There is a bunch of confusion out there...hope they all figure it out and feel like schmucks for telling me I'm wrong...when I'm trying to help.

I don't know .......but I've seen you say it time and time again. thanks for holdin back. LMAO

 

[harrisonm]

The post above your proves wrong too.
Lol did you miss that?

I guess I COULD be wrong. It did happen once before. I think I'll buy a few thermostats and test them in a pan of water.

 

[Ironracer]

I guess I COULD be wrong. It did happen once before. I think I'll buy a few thermostats and test them in a pan of water.

I've done that, a few times, and probably won't ever again. Lol. Mo need

 

[Ironracer]

Ratings on anything anymore it seems have a wider tolerance band than it used too

China Junk has us all, to an extent. It's hard to get good , quality Mo.Parts

 

[Ironracer]

Also my engine now runs at 180-200 instead of 160-180, so the thermostat definitely has an effect on operating temperature.

Here's what i know. Had a water neck rot issue with my ol '02 Ram, replaced it , and parts guy said factory recommends 195. I was running a 180. Truck ran killer, even though it had 280,000 miles. Put that 195 in, it about Fried my 5.9, going to Publix and back (1 mile each way), took it out, put in a 180, back to normal. I Have to side with RustyRatRod on this. Shoot, the Napa 195° is in the winder sill at the old house....reason I say this. I had a Very Accurate Temp Gauge on that truck, plus, a factory one. You could "see" the temp climbing, from a Cold Start, effectively " watchin" the T - stat open

 

[MOPAROFFICIAL]

That's a known trick with the magum 5.9 computer controlled. they like the 180 stats. Only aluminum head **** likes 195, that's self explanatory really.

They SAY carburetor engines like 170-180 stats...since carburetors dont really like heat...vapor lock,heat soak...again kinda self explanatory .

No body ever asked me...but I have run a 165 high flow mr.gasket for 20 years.
That's apart of my ragged edge tunabilty angle with running a cranking compression of 185 on 91 crap. My truck has a 180 because of the cracking heads initially..but it runs better overall...and in reading over the years to follow..I found that echoed on many forums and websites selling power adder,chips ,intakes,exh.. etc..

 

[BillGrissom]

The T-stat doesn't control an exact temperature. As the coolant gets hotter, it opens more, perhaps going from full closed to full open over a 10 F temperature change. Under high thermal load (summer, driving long up steep grade), you need more coolant flow so the T-stat will be open more than in winter. To be more open requires a higher coolant temperature. Any engineer should know that as "proportional offset" in control theory.

Testing in a pot of water needs to be careful to draw firm conclusions. My 1984 M-B diesel car once was consistently running 60C when ideally 82 C. The T-stat seemed to work fine in a pot of almost-boiling water, but when I tested it against a new T-stat and some Mopar T-stats, it appeared to open sooner and respond more sluggishly. Swapping in the new T-stat made the engine run at 82 C. Too low an operating temperature will give poorer economy and more ring wear.

IR gun thermometers work best on a black surface. To get an accurate reading, the surface must fill the whole view of the detector, which I am guessing is much larger than the tiny laser spot. Note that laser is not involved in the measurement and is only for alignment. You need to get the gun close to the surface to insure that. Try various locations, like the upper radiator hose. Generally, you will read lower than the actual coolant temperature. Perhaps more accurate are the radiator caps with integral thermometer. That said, I was amazed how closely the IR gun readings were to a mercury thermometer placed in the hot water, even shooting thru the water at a shiny T-stat. The problem in-car is more that the surfaces you are measuring are actually cooler than the coolant, due to convective heat transfer to the air.

As a mechanical & aerospace engineer with multiple degrees and published papers in heat transfer and fluids, I should add that car hobbyists have strange and confused ideas. Many swear that adding a flow restrictor improves cooling. Their reason being that otherwise "coolant flows too fast thru the radiator to cool off". How do they come up with this stuff? A Robertshaw engineer also wondered and found the source of this myth (google). If true, then wouldn't the T-stat be working backwards (opens more to cool)? Another is that the T-stat is constantly cycling open and shut as you drive. I'd believe that if someone gets an endoscope video of it happening. I doubt Robertshaw would design their T-stats to exhibit "negative feedback instability". More reasonable is that it reaches a steady-state position between full-closed and full-open. Rant all you want, engineers will not entertain your unschooled ideas.

 

[AJ/FormS]

To go along with what you, BillGrissom, are saying, I offer this corroborating story.

Many many years ago, I hung a bunch of same-rated, mixed new and used, stats in a big pot of water, by threading a tiny SS wire between the moving valve and the outter ring. Then I cranked up the heat with a thermometer also suspended in the water.
What I observed was that as the water temp increased, no two stats began opening at the same temp, nor did any two reach full open at the same temp.
I noticed that there were three different designs of stats in that pot with various sized outer "restrictor" rings, and so also various sizes of valves.
I could not find an accurate correlation between the areas of full-opening between any of them, except that some designs had larger full-open areas than others.
One of those was a hi-flow type and seemed to open faster than the others once it began opening, even tho it was late to the party. I thought that would be a good thing for my brand new alloy heads; so that is the one I installed. it was rated 195.
By IR gun thru the rad spigot and measuring thru the water, and bouncing off the cores. the water temp came up to ~205. I then hunted for a spot near the stat housing that ran the hottest, and was surprised to find two spots, one on each side of the stat house that ran a couple of degrees hotter than elsewhere. I marked those spots with black, felt-tipped marker, over the Orange-painted alloy intake. The Edelbrock heads were also painted several coats of Mopar Orange.
Over time, I measured those black marker spots, and they pretty consistently would end up at 205 to 207.
It would be impossible for me to say if the stat was fully open or not, as I cannot see into the housing. Since 2000, this stat has been working flawlessly. The box it came in was marked Milodon.
I suspect that the stat is in fact full open, as I installed a HD FORD thermostatic fan clutch,on a Seven-blade hi-attack angle fan, that limits the max water temp to 207 no matter how hard the engine is running.... or not. Between the two of them, once the engine is up to temp, it runs , by IR checking, between exactly 205 to 207.
The temperature drop in the ancient factory 26"rad, from top to bottom is 25 to 30 degrees.
Why did I choose a 195 stat for my HO 367?
Well;
partly to embarrass friends who insisted I needed a 160 stat; I'm kindof a rebel like that. and
partly because a very famous man once wrote a book and said to run my engine as hot as I could, short of a melt down. and
partly because I already knew that for max fuel-economy my engines always responded to running hotter, and this engine was built to be a daily driver, and to run on 87E10 because at that time, it was my best choice.
This engine has run 3 different cams, 3 different ratio manual transmissions, numerous different rear gears, and ended up very early in life with a GVod.
The best it has done is 32mpgUS, and the fastest track time is 93 in the Eighth (different cam).
It now has over 100,000 miles on it and has outlived the body.
That same hi-flo is still in it.

 

[MOPAROFFICIAL]

The T-stat doesn't control an exact temperature. As the coolant gets hotter, it opens more, perhaps going from full closed to full open over a 10 F temperature change. Under high thermal load (summer, driving long up steep grade), you need more coolant flow so the T-stat will be open more than in winter. To be more open requires a higher coolant temperature. Any engineer should know that as "proportional offset" in control theory.

Testing in a pot of water needs to be careful to draw firm conclusions. My 1984 M-B diesel car once was consistently running 60C when ideally 82 C. The T-stat seemed to work fine in a pot of almost-boiling water, but when I tested it against a new T-stat and some Mopar T-stats, it appeared to open sooner and respond more sluggishly. Swapping in the new T-stat made the engine run at 82 C. Too low an operating temperature will give poorer economy and more ring wear.

IR gun thermometers work best on a black surface. To get an accurate reading, the surface must fill the whole view of the detector, which I am guessing is much larger than the tiny laser spot. Note that laser is not involved in the measurement and is only for alignment. You need to get the gun close to the surface to insure that. Try various locations, like the upper radiator hose. Generally, you will read lower than the actual coolant temperature. Perhaps more accurate are the radiator caps with integral thermometer. That said, I was amazed how closely the IR gun readings were to a mercury thermometer placed in the hot water, even shooting thru the water at a shiny T-stat. The problem in-car is more that the surfaces you are measuring are actually cooler than the coolant, due to convective heat transfer to the air.

As a mechanical & aerospace engineer with multiple degrees and published papers in heat transfer and fluids, I should add that car hobbyists have strange and confused ideas. Many swear that adding a flow restrictor improves cooling. Their reason being that otherwise "coolant flows too fast thru the radiator to cool off". How do they come up with this stuff? A Robertshaw engineer also wondered and found the source of this myth (google). If true, then wouldn't the T-stat be working backwards (opens more to cool)? Another is that the T-stat is constantly cycling open and shut as you drive. I'd believe that if someone gets an endoscope video of it happening. I doubt Robertshaw would design their T-stats to exhibit "negative feedback instability". More reasonable is that it reaches a steady-state position between full-closed and full-open. Rant all you want, engineers will not entertain your unschooled ideas.

Here we go...the engineer has spoken..

No one said the t stats sets the temperature, though if it were to open late...it will control the temp in a bad way....but with a functional t sats rated properly we all know the temp varies under various loads, part throttle, wot...etc..and that would be the engine and its coolong system capacity responsible..but still not solely..which I'll point out in regards to your crap example hearsay from the 90's driveled by Chevy dorks and stoked by..you guessed it 'engineers' who rattled off their expertise to morons who misconstrued the idea.
To clear this more...No one EVER said to restrict the radiator...the idea at one point 'and this puts the cooling system capacity is in question here as the cause'...was... that someone got the idea the coolant was passing the cylinders and going through the heads too fast to dissipate the heat...so instead of matching the system...they thought to engineer some restriction.

If a pot of water 'small controlled area of consistant/controlled temperature' isn't a good testing ground... then it must be because you aren't the one testing it? Bullshit. You can believe that all you want.
You're doing something wrong, engineer.

 

[MOPAROFFICIAL]

I wonder ...do some pop up to rattle off against a non existent argument just to flex some delusional superiority?

Is it a argue just to argue or...like Pittsburgracer said... make it seem harder than it is? Overthink and overengineer it...

Do we realize 2 degrees or 2 hp in the end...did it matter to anyone but the creator behind the facade

 

[Dana67Dart]

IMHO...
There must be a time element to heat transfer.

Move your finger through a candle flame.

Move it fast no burn (less heat transfer from the flame to my finger)

Move it slowly and I get burned (more heat transfer to my finger)

Or am I missing something here?

 

[AJ/FormS]

Or am I missing something here?

I think yur spot on.
The water in the block is at say 180 to 200. The combustion temperature at idle might be 500, at WOT maybe 800/1000.. But by the time the expanding gasses have done their work; ~1/3 of the heat has been converted to energy, ~1/3 is going out the exhaust, and ~1/3 is transferred to the cooling system.
You wanna keep the heat in the head (as opposed to down in the cylinder walls), as much as possible, cuz the water up there is already hot and moving towards the rad. If you start the burning process too late, then the cylinder will get too involved, sending even more heat into the block, and HOTTER water into the heads.
So, yes you gotta move that heat, as quickly as possible cuz in a few milliseconds, more is coming.
If the water boils next to the confines of the chamber, it can no longer absorb heat, so it has to be kept moving. The slower it moves the greater the chance that the molecules next to the hot surfaces will boil, which will disrupt all the molecules around it, until it settles down. This is a bad situation.
The internal surfaces of all the engine have to be kept below the boiling point of the coolant. NOT all of the coolant is at the same temperature all of the time. The heads are the hottest.
The piston crowns likely the next hottest and they are not even in contact with the coolant! If the pistons swell up, it's gonna take away power from the crank. You can't let that happen.
If the pistons get too hot, you can bet they will share it with the rings, and if the ring-gaps close up, that will take power from the crank. You can't let that happen. The coolant cannot be allowed to boil, no matter what. I'm not talking about boiling in the rad; but rather boiling anywhere next to the heads and water jackets. So by your finger-in-the-flame analogy, it better be kept moving.
But there is nothing wrong with running the Minimum coolant temperature, as determined usually by the thermostat, at any temperature so long as the coolant next to the hot surfaces, never boils.
Because I have alloy heads, I chose 205.
I run a 7 pound cap, cuz my system is ancient, and it survives. Heck my rad is a 1973 model with patches on it's patches.
But I depend very heavily on that 7-blade, hi-attack angle, all steel fan and the thermostatic fan clutch, to not let the coolant rise much past 205.
and the hi-flo pump helps with that.
and the roadrace oilpan has a lot of radiating area, plus extra oil in it, and the cylinder wall squirters are working, and I send extra oil to the valvesprings. So all of these measures ease the load on the cooling system.
Yabut some of those measures cost me power right? So does damaging an engine, even invisible damage inside the cylinders, that you don't even know is happening until she starts to blow oil.
My car was a DD for many years, and so a few hp lost is/was cheap insurance. She now has well over 100,000 miles on her so I think it's working.

 

[MOPAROFFICIAL]

IMHO...
There must be a time element to heat transfer.

Move your finger through a candle flame.

Move it fast no burn (less heat transfer from the flame to my finger)

Move it slowly and I get burned (more heat transfer to my finger)

Or am I missing something here?

Then use a smaller radiator or 6 blade water pump.
Some of you are on autopilot or something. Complete the thought. Lol

 

[BillGrissom]

Here we go...the engineer has spoken..
No one EVER said to restrict the radiator...

If a pot of water 'small controlled area of consistant/controlled temperature' isn't a good testing ground... then it must be because you aren't the one testing it? Bullshit. You can believe that all you want.
You're doing something wrong, engineer.

A quick google would find many hobbyists claiming that adding a restrictor in the coolant path can solve an overheating problem. That has been claimed vehemently here too many times. Google further and you might find the writeup by a Robertshaw engineer who apparently found the source of this false idea. It was a solution for early flat-head V-8's which would burp coolant out the radiator due to excessive water pump pressure, which was problematic, but a different problem. The easiest counter to this absurd claim is to ask the genius if perhaps the T-stat should then be designed to close more as coolant temperature rises.

No idea what you are fussing about re the hot pot of water tests. For everything I state, it is not my word to trust, but the words in multiple engineering textbooks. I suggest you read them, then report back to us, or write a letter to the author telling him why his Physics is wrong.