cfair

My '66 Starfire (AC equipped) runs a little hotter than I'd like. My standards are extremely conservative, but I'm near SF in CA where you can count on traffic so I want my cooling system rock solid for when I get stuck in traffic I can't bail out of. I'm getting used to 190F, but still feel much better when the car holds 180F at idle in traffic. It's been running hotter lately, so I earlier this summer I did a little maintenance:

Did a 4 hour run with Thermocure (evaporust product) from my place to Napa & back a few weeks ago. Then flushed the h*ll out of the radiator, heater core, and block 6x or more til it ran clear. Stuck on new radiator hoses just for good measure. Then refilled with 70% distilled water / 30% antifreeze and 2 bottles of water wetter. My '66 big car holds 17 quarts so that's 3 gallons of distilled water, a gallon of green (original recipe, not eco---) and 2 bottles of water wetter.

At the end of all that work, the car ran hotter! D*mn. My radiator has been well maintained and you can see well down into the core, so I'm pretty sure it's not blocked. Swung by my A/C/Radiator shop and the owner suggested that I replace the thermostat. It's older - maybe from 2016 or so and 170°F.

O.k., so tonight I had time to swap in the new thermostat. When I do this, I test the new ones on the stove in a pot of water with a meat thermometer just to prove to myself that it'll open as advertised at whatever temp I bought. From the markings on the old one, I think it was a 170°F. The new one is a 160°F. Both are high quality Mr. Gasket / Robertshaw high flow style.

Here's the fun part:
On the stove tonight the 170°F the thermostat I pulled out opened fully at 180°F. That is within spec.

Thermostats are known/advertised to open fully 10 degrees plus/minus their rated temp. I'm not sad/upset/etc at the old one, though it did have a few weird bulges in the heat sensitive wax stuff which may have been impeding coolant flow.

The new 160°F thermostat was fully open at 170°F which is good news since this an AC car & runs a tick hotter than I'd like in CA weather with the AC compressor on.

Main points 1) test your thermostats before installation; 2) dont' be surprised they're fully open 10°F above their spec'd opening point.

Cheers
Chris

Vista67

"Both are high quality Mr. Gasket / Robertshaw high flow style."

Chris, I am also in the SF Bay Area and had similar issues with runaway coolant temps on hot summer days in both traffic and freeway driving. I replaced the Robertshaw high flow thermostat that had been in there with a new one as one of the first troubleshooting measures and it didn't seem to help. I then went through and upgraded pretty much everything else in the cooling system and made some progress but didn't completely solve the hot weather issues.

I went back to the beginning and measured the full open passages in a number of new and old thermostats. Just based on max opening at full hot, the reverse poppet style Robertshaw units were the winners with the largest flow area. However, the design of the Robertshaw sends the coolant around the outside diameter of the cylindrical part of the thermostat that sits below the mounting flange on the intake. With conventional style thermostats that open up to flow through the middle of the thermostat, the flow area you get when the thermostat is in a pot of water being tested on the stovetop is the same flow are you get installed in the the intake. With the Robertshaw style, the actual flow area is determined not by the thermostat but by the upstream plumbing before it gets to the thermostat opening and through to the radiator. With the Robertshaw anything flowing to the radiator has to pass through the area between the outside of the thermostat poppet cylinder and the inside ID of the thermostat flange in the intake. For every Olds intake I measured, the intake mounting flange to Robertshaw clearance severely restricted max flow to the radiator versus what would pass through the Robertshaw thermostat itself. I replaced the Robertshaw unit with a high flow conventional style center flow thermostat and have not had an overheat incident since.

Just try switching back to a OEM style, center-flow thermostat and see how it runs for the rest of the summer.

I have the thermostat and intake flange measurements and calculations in a spreadsheet I can share if you pm me.

For other makes the intake restrictions may not come into play and in that case the Robertshaw may provide higher flow capacity and better temperature control as claimed. They probably use the same center cylinder section on all the Robertshaw parts and my measurements suggested that that center cylinder has too big an OD to work with the flange ID on the Oldsmobile V8 intake.

69HO43

Firstly, I'm going to throw some spaghetti at the wall and see if anything sticks.

Do you have a fan clutch? I'm assuming so, with A/C. Just a wild guess here, but if everything has stayed the same but you're temps are creeping up a bit, maybe your fan clutch is kind of working but wearing out? If it runs cool all day long on the open road, but only is hotter in traffic, maybe check that. In general, you can determine if your clutch is bad or going bad. First, inspect it for any leaks. Fluid with dirt build up around it at the shaft is a bad sign. Turn the fan by hand when cold. It should turn smoothly, but easily and not wobble on the shaft at all. If it's rough turning, or "stuck" or wobbly, it's already over. If not, then start the car. With the engine running up to operating temps, watch it as someone shuts off the engine. The fan should stop in 2 revolutions or less. Just because you hear the "roar" of the fan clutch coming into play as things heat up, doesn't mean it's in perfect operating condition. If the clutch is starting to fail, you may not notice but the max speed it pulls air through the radiator in traffic will diminish, and thus temps could start creeping up.

Additionally, you may have had crud building up around the coolant temperature sensor. By cleaning out the system, you may have removed that insulating crud, and now are receiving a more accurate signal. That may be why you are seeing a tad higher temp (more spaghetti tossing)?

As far as t-stats go, degree ratings are the advertised nominal setpoint in which the t-stat starts to open. It is generally acceptable for it to be fully open by 20 degrees on top of that. So if it's full open by plus 10, then you're good. And thermostats aren't built with a super-tight tolerance, so the ratings are nominal. Some open a tad later than others. But thermostats only set the floor temperature for the engine, nothing more.

GM loved 195 t-stats. One of the main reasons was for quick heatup to normal op temps (NOT) and driving off moisture. Recall most engine wear comes between startup and less than 170 degrees. Engines were designed and built around that so clearances would be in the normal range at NOT.

There is only ONE reason you should consider a 160 degree thermostat, and that's if your overall coolant capacity to remove heat is enough to do so, i.e., system sizing, air flow, and coolant flow. Once the thermostat opens, the capacity has to take over. If you have sufficient capaicty, you could actually run too cool, below deisred normal operating temperature, to a point of even cycling the thermostat, to which it was not really designed to be a regulator. The only reason I would ever consider a 160 t-stat is if I had the spare coolant capacity to run that joker hard and often. You have more of a "buffer overhead temperature zone" before you reach your limits. Mass flow rate, both air and coolant, is your friend. Difference in temperature also is a big factor, but not as easy to change as mass flow rates. The more the better (obviously to a point) will increase your overall heat transfer.

On the flip side, your system may need maintenance, and if so, capacity may be reduced to you overheating in certain situations no matter when you open the thermostat. But generally speaking, the opening temperature isn't going to do much as it effectively turns into a bystander once fully opened. Vista67 might be on to something with these huge poppets on the Robertshaw style T-stats may actually cause some flow restrictions due to design. I have used them in 455s before, but not on on the 80s models with computers. The 80s CCC cars were designed for emissions and that's why they get the stock t-stats. In any case, the only overheating issues I've ever experienced is when I've had component failure. Once with a blown head gasket incident, a torn rad cap gasket, and a stuck closed thermostat. Not fun in any case, but I've never had a problem under normal operating conditions using the AC Delco stock t-stats.

There are also several references I've read where GM has determined it's acceptable to run below 240 degrees without harm.

I've had no issue running the 195 stock ACDelco T-stats on the CCC cars, and 180 thermostats on the 455 cars. On the 71, the mechanical gage read about 200-210 all day long in traffic, and I've never had an issue with that.

There could be other reasons you want to choose a lower t-stat opening temperature, such as highly modified engines where you're not that concerned with gradual wear. But generally, on your stock units, there's not much of a need for anything other than stock parts.

66_Jetstar

A few things come to mind..

I'd say you're on the right track. However I would be super concerned about the radiator at this point. There is no doubt that with it's age it has some blooming going on along with some corrosion. The flushing moved alot of grime and deposits around. unfortunately lots of that muck probably settled in the core passages, which were probably already somewhat partially blocked. I would get an infrared thermometer and do a thorough check of the rad for cool spots before throwing any money at it.

Waterpumps move volume but they dont really generate much psi. They are rather lousy at forcing coolant through restrictions, your garden hose makes more psi and can push its way through the nook and crannies, so that test can be misleading.

RWK

I also did the thermo cure, but it was in engine a few days and a few trips, then several flushes with good water, (DI), fill, run up to temp and drain, took all day.
My engine is well worn, 137k and don't have much history on it, rad was repaired at one point but it seems ok and flows fine. engine is a 455 no ac, std 4 blade fan 3 core rad. it runs 190-195 now or NOT, gets to 230 sitting at idle or creeping in traffic which I feel is fine, as soon as I start moving drops right down to 190, I ran the stock thermostat 195 and now run a 180 stat, engine runs same temp regardless, factory temp switch is 245-250 I believe according to CSM. I monitor temp with a thermocouple in stock sender spot and a digital industrial gage which is very accurate, About Us | The Sensor Connection Motorsports Temperature and Position Sensors, another thing that many forget is the trans temp contributing to heat also, assuming you have an auto, I have a TH400, i did add a small 696 Hayden stacked plate cooler after the rad. so trans temps should be cooler then engine 180-190~

jaunty75

There is nothing wrong with idling at 190F or even 200 or 210. You are obsessed with getting to an unrealistically low temperature (which can be just as bad for the engine as too hot) and spending time and money trying to fix what ain't broken.

My advice is to remove the temperature gauge, put back the idiot light, and drive the car.

cfair

Jaunty - with you in spirit, but I’ve had a few scares on hot days boiling over through the years & my brother killed an Olds 350 in a 73 Vista Cruiser with a boil over, so I worry a little.

This time it wasn’t so much the absolute temperature the car reached that worried me. It was really that the cooling behavior was measurably worse than before all my well-intentioned maintenance. Why?

The end of the story is I got and installed a bad fan clutch, it just didn’t pull enough air. What’s funny is I got the exact same part number as was on the car. It just didn’t work as well as the old one. Since I’d gotten to the end of my skills, I fell back on my favorite mechanics who specialize in A/C and Radiators. The confirmed that the radiator was clean & clear - very clean and that the heater core had not gotten gunked up with engine coolant jacket debris.

Then they installed a Delco fan clutch which seems to have returned the car to normal, maybe better than before. Yesterday was on 78°F on my drive home, but the car did seem a lot better at last.

I got the impression that copper/brass manufacturing is declining. I’m thinking I might get a spare radiator built and stash it in my hoard. Worrying too much again? As these cars are pushing 60, the knowledge and parts seem to dwindling….

Thanks all for your sensible advice and thoughts.
Chris

CANADIANOLDS

the advice given here on temps is some of the worst I’ve ever seen.

heat kills power and performance..unless you’re stuck having to meet some weird emissions regulations or are hell bent on putting up with excessive heat because of stubbornness, don’t run the engine really hot.

even the most basic grocery getter Olds from the 60’s and 70’s that isn’t driven in winter should be set up to run cool…in the 160 to 180 max range. GM built them as year round cars..do any of you actually drive them through freezing winter conditions?

you all know what it feels like on a hot day when the engine temps skyrocket to 200 or more, they feel like they lost a couple cylinders and are way down on power…that’s because they are way down on power ,,, the engine is cooking itself

why would you want that? on basic bread and butter stockish builds i put in a 160 stat, on performance street driven stuff I use a 140. they run the same temp in hot or cool weather and do not run way off high on the max temp . I also block the intake manifold heat crossover on all builds unless it’s for year round cold winter use.

RWK

To an extent lower temps are ok, you will leave HP on the table at too low a temperature also, heat makes HP also, to an extent also.
I believe designed normal operating temp of an engine is the best temp, my 72 455 runs at 190-195 which is it's NOT, you run an engine at 160 or below what is your oil temp, piston clearance? you are using more HP to pump cold and thick 140-degree oil around an engine, not to mention oil lubes and flows better when warmer, engine and trans oils are designed to operate normally at between 170-220 efficiently. Purpose of a thermostat is to allow the engine to get to it's NOT, and keep it there, it is where all clearances (bearing, piston) are in spec and oil temps/viscosities are optimum, this is especially true in diesel engines.

CANADIANOLDS

^^^^dont believe any of this^^^^

what the heck does this mean “purpose of a thermostat is to allow the engine to get to it’s NOT , and keep it there” ?

RWK

You don't understand a thermostats function or the acronym for normal operating temperatures?

VC455

That spaghetti sticks to the wall. It's a fact that few appreciate.

RWK

oldcutlass

A thermostat is designed to bring the engine up to and maintain the minimum operating temperature. Not the NOT.

cfair

I’ve always thought of the thermostat as the device which sets the temperature lower bound, once it’s open, you’re using other components to achieve desired temps - chemical, mechanical and thermally activated.

Chris

69HO43

Absolutely.

Koda

The statements about a thermostat being designed for a floor temperature only are a canard thought up by someone whose radiator is not up to the task.

Let's talk about OEMs for second. Not "dude in his back yard building up a 442," let's talk about the original designers. Automotive theory is as such: The radiator is designed to provide excess cooling to all needs of the engine, and, left wide open, would keep the engine at an undesirably low temperature, like 140 or something. (and 140 is a number I just picked, it doesn't mean anything.) The thermostat is there for one function only, which is to regulate the temperature. When the engine is cold, the thermostat is closed, and that aids quick warm up. When the car is at operating temperature, designated by the thermostat rating, the thermostat will vary its opening to regulate the amount of coolant going through the radiator. It is not a light switch, it can vary. Thusly, a properly regulated and cooled system will stay at the rated temperature. This is why new cars stay at 50% of the temp dial no matter what you do, they are properly regulated.

A lot of our older cars have funked up radiators that their owners think run fine. The car warms up, the thermostat is opened wide by the demands of the engine, and the radiator cannot maintain the thermostat's rating, so you go from 180 idling, to 190 in traffic, to 200 on the road. That works, and it's fine, but it is not as the system is designed. Some people have a variation of this, the car stays at thermostat temp except when running hard. This means the radiator can provide excess cooling to 90% of the car's needs. Some people have theirs properly regulated and idle vs traffic vs highway is no difference. I took a car that would run hot, through a 160 deg stat, and it ran better but was still all over the place. A 185 stat and a NOS 3 core radiator keeps it at 185 all day long now.

The reason this happens, and the reason that people are cool (hah) with running above a thermostat is that it works. It works due to Newton's law of cooling, which is, the greater the temp difference, the more efficient something is. In practical terms, the hotter the radiator, the more heat it can dump since it's got a higher temp difference to ambient. As such, a lot of cars can run hot all day long, and not boil over, because running hot enables the radiator to keep up as it is more efficient. But, it is not how it is designed.

69HO43

Seems to be a misunderstanding between thermostat function and coolant system heat transfer capacity. Fine by me. We can simply agree to disagree. A thermostat is not a regulator. Never has been. Never will be. It's just a door. There's no feedback from anything downstream. It's all upstream sensing. It opens when it senses coolant is hot enough to its setpoint, which isn't super-exact but should be pretty close, and it should be fully open likely within 20 degrees above the setpoint opening temp. It will close when it gets a bit below the setpoint. Pretty ingenious, yet simple design. But no regulation features. I find it a bit odd you described the function of the t-stat's floor temp, but say it doesn't do that. Hmm.

We can do you one better. Per the CSM, you can take the suspect thermostat, put it in water, start heating it up, measure the water temp, and watch if/when the thermostat starts to open. Out of the car it opens and closes. It simply opens, or it closes based on the setpoint. It doesn't regulate anything but is doing exactly what it would be doing inside the coolant system. Just opening, and closing based on exceeding or coming in below its setpoint.

Let's take a look at that 185 thermostat example. 185 all day long with a 185 stat means your floor temp is 185. Whether you run it hard or not, the temps not going to be getting below 185 very much while operating. If it does, it won't stay there for long. You can have an entirely new system with everything operating properly and your thermostat is going to want to make your engine sit there and get to...wait for it....185 on coolant temp before it starts to open. You will not run, say, a constant 160 with a 185 T-stat installed, ever. Won't happen. Why? Because your floor temp is 185. Thermostat stays closed until it reaches 185 and then it starts to open. Want to change that? Put in a 195 thermostat and then see what happens. Floor temps get reset to 195.

Don't forget that mass flow rate (water pump's function) has nearly everything to do with a fluid system heat exchanger besides the differential temps. Newton's law basically looks at area, but thermodynamics looks at mass flow rate and specific heat capacity of the fluid (typically a constant). Q = m x cp x (Th-Tc). Higher the mass flow rate, the more heat transfer. I know this flies in the face of those who believe in "residence time" in a radiator, but in a closed system, you can't have it moving any faster or slower through the radiator than the block and hoses. So if you slow it down through the radiator to expel more heat to the air, you also have to slow it down in the block to pick up more heat from combustion process. Not winning any prizes doing that. This is why the older TVS systems port full vacuum to the distributor advance can when the car starts to overheat. Adds a bit more timing at low rpm and increasing timing raises the rpm slightly to increase water pump speed, thus raising mass flowrate of the coolant, and hopefully the fan moving a little faster pulls more air across the radiator. Hopefully enough to cool it down and not boil over. Thermostat is wide open the whole time this is going on. You are simply manipulating the rest of the coolant system's properties to increase efficiency.

Thermostats set the floor of the engine coolant during operation. Period. Nothing more. Once it fully opens (and it can be debated what means "open" for a thermostat), theoretically it is out of the equation until/unless coolant system capacity is good enough to bring down temps to below the T-stat setpoint. If you have coolant system CAPACITY to cover the heat transferred to the coolant from the engine to the radiator, and the air flowing across the radiator to remove that amount of heat or more, then good for you. You can run it hard and not overtax the cooling system because you have some headroom to be able to remove the excess heat generated above the t-stat setpoint. Systems were designed to ensure the coolant system as a whole had the capacity to remove the extra heat in many situations. I do understand that equations by themselves aren't always real life, because proper maintenance needs to be performed to ensure everything is running in top condition, and this includes the coolant system, which can be in 25 different environments on a single Sunday drive. Dirt/crud and poor components can cause the capacity to diminish and you end up overheating due to loss of cooling capacity, not a t-stat setting. In any case, whether the system is in poor condition or not, the t-stat won't open until it reaches the floor temperature.

I'm totally open to someone proving this wrong. But this is how I see it. Convince me otherwise.

Fun71

I agree with whats said above by both of you.

One thing you overlooked about your “door” analogy is that “door” can be open anywhere from a slight crack to fully open - it depends upon the coolant temperature.

CANADIANOLDS

unbelievable…will you pay for his repair bill when he cooks the engine?

his goals are not at all realistic..they are correct and he’s on the right path

CANADIANOLDS

straight out of the dictionary….a thermostat is a temperature regulating device that maintains a desired set temperature.

having been an HVAC tech for 40 years…I’m pretty sure I understand what a thermostats function is. there is an over/under range for stats. they can be normally open or normally closed. they are normally closed in auto apps and open on temp rise, then close again on temp drop. they are designed to maintain a specific temp range around the min set point …

they absolutely do regulate engine temp…that’s why they’re called t h e r m o s t a t s

Koda

The only disagreement we have is over a semantics point, which you resolved with your second paragraph.

The engineer in the desert gets full marks.

As does the Canadian.

CANADIANOLDS

Hi 😂😂😂

66_Jetstar

Yikes. What the hell happened here?