Get the lowest one you can. The way it works is that number is the temp at which it opens so the motor will not get below that temp once its warmed up. So I like a 160*F so that it opens at a lower temp and pretty much stays open all the time

 

But it should be mentioned that mod wont help a cooling system that isnt up to the task of maintaining temps... and if by chance after the correct fan and shroud goes on, the stock style cooling system works correctly with what I assume it not a stock motor with stock timing at this point. Most would agree the 160 degree stat is not as ideal as the 180. With the 160 stat the engine will wear faster and make less power at least thats what I read over and over when comparing them for my car.

 

If you like a hot engine and less power thats fine

 

A 160* stat is better for racing to keep the cylinder/head temperatures a few degrees cooler when the fuel being used is borderline on detonating. For street cars, as already mentioned by augiedoggy, a 180* is the better choice for maintaining the oil temperature at its optimum for lubricity. But, if only a few thousand miles per year are driven, then a 160* stat should suffice provided that the rad has the capacity to maintain the engines temperature at 160*. If the rad can't cool the coolant quick enough then then what's the point of a 160* stat if the engine will run somewhere above that temperature. Reading comments on cooling systems indicates to me that most folks don't understand how a cooling system works especially with regards to the thermostat.

 

If you pull the thermostat and drive the car around you will see what the cooling system will maintain the car at. THe car will maintain and equilibrium based on the air flow through the radiator at a certain temperature for a certain amount of power. ITss a catch 22.. power=heat. To make power you want lower heat, but making power creates more heat that needs to be removed....
my old hi-po 327 with the stock air dam, M20 and radiator would stay at 180* at 40-50mph. increase that to 65 tp 70mph and it would get about 200*F. 75 to 80mph and it would be around 4000 rpm and 210*F. If it was a hot day it would go up from there. Adding a bigger air dam increased the flow through the radiator reducing the temp down closer to 195 on the highway. in the fall the temps would stay closer to 180 on the highway and 160 which was the thermostat setting on the backroads. THe hot beach traffic would get that motor up to 210 and hotter fast . the new clutch fan couldnt keep up with the hot asphalt and no airflow. Upgrading to an electric fan that had a tight shroud and seals so no air could get through the fan without coming through the radiator kept the beach temps below 200*F easily

When I put in the big block radiator and 5 speed last summer it would stay at 180*f on the highway and below that on the side streets.

Now with tthe big block and the cool spring temps it doesnt get above 170* below 60 mph and 80 tp 85mph on the highway it hasnt been above 180*F

The thermostat will help increase the operating temperature to not go below that set temperature. Put in a 190*F and it will not run cooler than 190*F, if physically can not do it once it achieves an operating temp above that temperature. The thermostat shuts off the cooling fluid flow. Whatever the engineer designed into that engine to achieve a specific emissions standard depends on that setting. Most new cars run hotter to keep the exhaust temps hot to get the catalytic convertor to do its job. That is how they are designed for emissions.

On our cars with a specific HP in mind and not giving a hoot about emissions standards, running it cooler is perfectly fine and advisable. HP is tied into engine efficiency, if it makes more power at a cooler temperature, then its more efficient, then its good for the motor. The heat transfer from the rotating assembly to the oil isnt going to change because the engine is operating at 180*F vs 200*F. But the cooler air charge and fuel charge will make a big difference, and the cooler the engine , hopefully the cooler the passenger compartment.

MY advice is to use a 160*F just to get the coolant flowing, if the engine operates at 180*F during city traffic, then its happy. IF you dont give it the chance to cool down or run cool and have a really high thermostat then you are defeating the purpose of a cooling system. The OP had an issue with running hot in stop and go traffic. That issue is the fan moving air thrrough the radiator and the coolant flowing. Use a lowerr T stat to get the coolant flowing. USe a good fan and shroud that causes the most air flow through the radiator. For me and my experience, a 160*F thermsotat and an electric fan setup are the best choices. especially if you are running an old mechanical clutch fan, in stop and go traffic the engine rpm is 800 rpm so the fan is only spinning at 800 rpm, not 3000 rpm where it can move the most air. If the problem persists and you get trapped in traffic, pop the hood open enough to help the hot air escape.

 

"If you pull the thermostat and drive the car around you will see what the cooling system will maintain the car at. THe car will maintain and equilibrium based on the air flow through the radiator at a certain temperature for a certain amount of power."

No disrespect but a lot of folks assume this to be true but it this will only lead to an overheated engine given the right conditions whereas a ts would prevent overheating under the same conditions. But what is that equilibrium? That totally depends upon the outside air temperature. The higher the ambient, the higher your engine temperature. And vice versa in cold climates. You are at risk of running too hot or too cold. No control whatsoever over engine temperatures unless you can control the weather. But that's why there are ts that do control the engine temperature regardless of the outside temperature and also maintain the engine temperature at or near the ts rated temperature. Those of us who have a properly functioning cooling system using a ts and gobs of HP, will agree. Those who disagree such as guys yourself who follow this logic and can't maintain a steady engine temperature under all driving conditions, have a cooling issue. Whether using electric fans or clutch fans, the radiator doesn't care as long as air is pulled through it. My oem 7-blade clutch fan blows more air at idle than twin Spal fans. So my idle engine temperature is the same as my cruise temperature, in any ambient air temperatures because I use a ts, have air flow through my rad and a rad of sufficient capacity to cool. So if you or others can't maintain a steady engine temperature, then something is amiss because lots of us can.

 

Thanks that is the point I was trying to make basically if your car's cooling system can't even maintain a 180ﾟ without going higher it's not going to do any better of a job of maintaining a 160.
And And no disrespect ment but according to everything I've been taught on this taking the thermostat out of a car is not a good idea what will happen is your car will run at all different temperatures depending on ambient conditions at that time and what that does is caused things to wear faster due to Different expansion and contraction rates of things running at constantly changing temperatures.

 

I understand that and agree. That was the point of the long story. At a certain power level the car will maintain a certain temp. If its lowest avg temp is 180*f, get a 160*f t- stat. They aren't magic and dont do anything other than let the engine heat up quickly to a minimum set point....I myself and anyone that likes power would want the lowest possible.

 

I guess the important thing to note is since we are getting off topic, is no matter a 160, 180 or no thermostat, if your cars overheating while sitting in traffic it will continue to do so until you can get more air thru the radiator at these times were either coolant or the air flow is inadaquet and causing the heat exchanger (rad) to not be able to cool efficiently.

As far as the stock fan pulling more air at idle than the spal fans running at full rpm without the very real limitations of engine speed and the clutchs temp rating. Well I dont want to get into a urinating contest here but I have already mentioned my very recent experience going from a new radiator with stock shroud and new clutch with stock fan to the dual spals above. My car has never run as cool as it does now with the single cooling system change being the fan. I just dont understand how if the stock fan really does move more air at idle, This could possibly be the case.

 

 

It's hard to tell from your picture. Do you have the shroud extension installed?

Fan Shroud Extension for 1973 with 454

 

The following pics are straight from the 1974 FSM. You guys will see that the ts does more than speed up engine warm up and set minimum temperature or in other words, normal operating temperature. Also note the test method for the ts trouble shooting. It shows that the ts should begin to open at 10* less than its rating and be fully opened by 25* above its rating. So a 180* ts does not open at 180* when engine load increases nor shut at 180* when the engine load is reduced. The ts is a valve that modulates between fully open and fully closed over a temperature range of up to 35* which is dependent on the rad capacity and efficiency to cool the coolant. Hence, it controls the amount of coolant entering the block from the rad to maintain 180*. So a nice big aluminium rad which gives capacity and efficiency will keep the engine at the ts rating of say 180* under most conditions and HP levels for street use. The engine temp should not rise the full 25* above the ts rating. If it does, then the cooling system as now at the mercy of the ambient air temperature and will eventually over heat.

The fan really is only a means to substitute the air flow volume one would expect to have at say speeds above 30 mph where the fan would not be necessary to cool the coolant in the rad. So whether its electric or mechanical, as long as it can draw the same volume of air through the rad as it would at 30 mph, then there shouldn't be any overheating issues in stop and go traffic.

A flow chart for overheating diagnostics is also included.





















Btw, even though this is out of a book from almost 50 years ago, the physics haven't changed i.e. its still current.

 

OK, you do have some problems to fix, BUT, 210 deg. is NOT overheated for a BB Corvette. It is more common than not, because of design features--slanted radiator, poor under hood air flow, etc.
It IS a BB. They tend to run hot.
Use good oil and 210 is not a problem. Full synthetics are generally better in all respects. I run Mobil 1 5w/20.
Per the water puking. My BB runs with the overflow tank less than 1/2 full when cold. If I raise the level, it will puke some out next time I run it. Usually, it pukes out more than just the little bit I added, so I need to bring the level back to the original level.
Also, are you sure your temp gauge is correct? Get a infrared temperature gun to check.

 

The shroud is installed, but the fan has 6 wings, which I think somebody said is not stock.
Also, there is quite a gap between the radiator / shroud and the fan, looks to me like the air being pulled in could easily go around the radiator.
How big should the gap be? As can be seen in the picture, it's something like 4-5 inches, but I guess I also don't want to go overboard and have the fan flap against the shroud...

 

I had to add 5 liters of water after it overheated, so there is definitely something wrong.
I guess it would make sense to change the oil and cooling fluid, just to eliminate bad fluids as a cause. Could be chocolate milk in there for all I know.
(Actually, the oil looks fine on the dip stick, so it's not chocolate milk, but there's no telling exactly what oil it is)
Good point about the temp gun, I did suspect that the temp gauge might be showing too little.

 

In your pic the fan is connected to a small spacer...the fan clutch may push the fan in further towards the raditor....

with the engine running if you hold a sheet of paper in front of the radiator, does it get sucked onto the radiator?

 

the fan is supposed to be part way into the shroud. so it should be small enough to fit in the shroud with 1/4 to 1/2 inch (5 to 10 mm?) clearance in outside diameter. your 2 biggest immediate problems are the fan spacer is too short and your radiator cap does not hold pressure. you could even do a half-*** longer bolts and stack nuts and washers on the existing spacer to see how that fan fits the shroud when moved forward. and you can fake up stuck in traffic by idling it in the driveway in gear.

 

Professionals call that "mocking it up" that way they dont get called "bubba"...

Just make sure those bolts are tight and dont over rev it, stacking spacers individually can get the fan off center with bolt variations vs a solid one piece spacer

 

I'm really positively surprised by the 73, you open the hood and everything is right there, and you can understand what everything does if you apply yourself (although I still have a lot of applying to do...).

Compared to my modern daily driver which is a complete mystery (it's a hybrid and if something breaks, you can basically throw it away).

Also thanks a lot for the pages, very helpful! I just ordered the 73 version of the that manual, but it'll be at least a month before it arrives, so this should help me get started sooner.

If I want to check the lower hose spring, there's no way to do that without draining the cooling system, right? There's the physics that haven't changed for 50 years again :-)

 

You can simply squeeze the lower hose when the engine is cool. If the spring is present, and intact, you will feel it, and it will prevent the hose from collapsing. If the spring is missing, it will feel squishy like the uppper hose.