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Discussion Starter · #1 ·
Still in the process of a carbureted 383 build. Got to the point of ordering some misc. parts. New thermostat and water outlet is one of those. Obviously there are some options for a SBC. Ranging from 160 degrees to 210 degrees. I know on modern, computer controlled, vehicles the ECU wants to see a certain coolant temp to enter closed loop. I know this also leans out the fuel mixture once the desired temp is reached. On a carbureted engine, does coolant temp have an effect on anything? The cooler the better?
 

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Click on above. I like these T stats. They start to open at 186 or 187 degrees F. I cut the bottom spring and disc off and use it in Gen 1 and 2 SBC's. You can take off the O ring if you rather use a gasket. For a street car, 160 is too cold. 180 is better and 195 is starting to get kinda warm. Especially if your water temp climbs up from there. 186 or 7 is about perfect for a carbureted SBC.
 

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200' water and 220' oil is good.
Remember the stat doesn't set the temp but instead the timing of when it begins to flow water(warm up time)
...unless the radiator is over sized.
 

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Runnng the engine hot at 210 is for greater efficiency, longer life, more power, and lower emissions.

- For greater efficiency to a large extent this drops out of aluminum heads and blocks. Aluminum moves heat faster which allows higher compression ratios and actually demand higher operating temps to put more energy to work rather than into the cooling system.

- Longer life falls out of reduced fuel wetting of the cylinder walls, oil temperatures high enough to drive combustion by products out which reduces acid, sludge and varnish formation and by not consuming the sacrificial oil additives so quickly as a result the oil goes further between changes.

- More power and lower emissions come from a faster and more complete burn, more compression and combustion pressures applied to the piston, and higher detonation tolerance through a more uniform mixture ratio cylinder to cylinder.

Now obviously port or direct fuel injection is a huge help with getting uniform mixtures from one cylinder to the next, but the added operating temperature does help with a carburetor and TBI as well by encouraging the fuel to remain in the mixture instead or precipitating out and pooling and running along the manifold floor.

You have to differentiate between what is good for a long lived street driven engine and what makes best power on a race engine without regard to life span. This is where at least for a carburetor the argument for a warmed mixture versus a cold mixture come into being. Port and direct injection get around the many vagrancies of intake manifolding problems.

The big issue with running at 210 degrees is there isn’t much space if overheat takes place for the driver to take action sufficient to save the day. But in reality we all are rather inattentive to gauges so I’m not to sure that this is an argument supporting cooler running.

For my own daily driver it is set up to run an unheated carb and intake on a ‘hot‘ waterless coolant engine. But it has modern aluminum heads and tight clearance high silicon forged pistons. What and how you should cool is in no small way connected to the materials and clearances of the parts used.

Bogie
 

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Engines like to be hot. Drivers like them to be cool.

I agree with Bogie on everything but the power part. Lowering the temperature lowers the amount of heat that soaks into the intake charge. It's not significant, but denser/cooler air means more mass that makes it into the cylinder for the same volume.

When I say not significant, we're talking about usually less than 10 hp with tuning and appropriate changes when going from a 160 to a 195 thermostat. For me, engine and oil health is more important than a few ponies.

Keep in mind that coolant's boiling temperature is set by the physical properties of the coolant, specifically dissolved glycols and radiator cap pressure. These determine the boiling point of the coolant which is the most important part of overheating. Temperatures inside a combustion chamber can exceed 2500F, so changing between thermostat temps isn't as big a deal as many people think. The most important part is preventing boiling. Once things start boiling, the water loses significant area where it is in direct contact with the water jackets. Once the boiling threshold is crossed, it's downhill from there.

That's a long way of saying - don't stress over it. I personally choose 180 or 195 depending on the setup. You want the oil to get hot enough to evaporate the junk and stay healthy, and the coolant to have an adequate buffer between the stat opening temperature and the boiling threshold.
 

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One more very important thing. Coolant temperature is 100% a function of the heat into it versus the heat out of it. This is where the difference between heat and temperature comes in. They are not the same. If the process of your combustion introduces 50 units of heat energy into the coolant, the rest of the cooling system has to be capable of rejecting at least 50 units in order to maintain stasis. The thermostat determines the temperature at which that transfer stops and starts. The temperature at which the stat opens is completely immaterial to that transfer of heat energy. If you take the thermostat out, the combustion is still giving the coolant 50 units of heat and the radiator is still shedding 50 units.

Overheating happens when your combustion adds more heat energy than the rest of the cooling system can get rid of. In that case, it doesn't matter what the thermostat temp is, it's still going to overheat.
 

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The 186 or 7 T stat I refer to in my earlier post is a stock unit used in a 2002 Camaro with LS1 V8. Lots of research and engineering went into the "new" L series engines in the nineties. These engines will easily run for 300,000 miles with routine maintenance. That's why I use that T stat. I agree too cold is not good for lots of reasons. I'll stick with the Chevy engineers recommendation.
 

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Discussion Starter · #8 ·
Thanks for the replies. Now that we are talking about accelerated where due to the lack of effective heat, my current 355 has a 180 degree thermostat, but doesn’t get above 155ish. Any idea why that would be?
 

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Yeah keeping the castings wet is vital to their survival, this is to a point more important than coolant temperature. As long as your able to hold off nucleate boiling the castings can be pushed well towards 300F.

In an engine there are hot spots that well the exceed the boiling point of most coolants. These rather obviously are exhaust valve seats and spark plug bosses. So when coolant temps get high these are the first places where it is likely that the coolant will locally boil even when the bulk coolant temp may be comfortably lower than its boiling point. When local boiling occurs then essentially the hot spot causing the boiling is dry and is free to enjoy temperature excursions to wherever the incoming heat energy will take it. Within a casting this excursion causes that metal to expand more than wetted cooler metal adjacent to the overheating hot spot. The end result when the forces exceed the strength of the material is you get a crack.

The reason for maintaining a pressurized cooling system is to hopefully keep these hot spots wet thusly transfering heat to the coolant which is the only chance of preventing a runaway hot spot in the casting surrounded by cooler metal.

Another way is waterless which when the curtain is pulled aside is essentially pure antifreeze of some sort which usually be mixtures of ethylene and propylene glycols. These have much higher boiling points well into the range of 350F at normal atmospheric pressure. The down side is they move less heat per unit volume so a cooling system sized for a 50/50 mix of water and glycol will stabilize at a temperature about 20 to 30 degrees higher. However, the advantage is that the hot spots have the potential at least to stay wetted without resorting to high pressure cooling systems. To a great extent this knocks down transient cooling system voltages that encourage corrosion between dissimilar metals. So this reduces to eliminates rust formation which has two major problems in a cooling system: first, rust is an insulator so once forming the heat transfer of the rusting surface goes down leading to that surface operating hotter or in a radiators tubes reduces heat transfer to the atmosphere; second, rust collects to plug passages starving those areas of surface wetness which leads them to local overheating. The big downside to waterless is it is flammable and slippery so most race venues ban its use which may well extend to water mixes as well.

I’m not selling the idea of waterless, although I use it, but I’m juxtaposing the difference in how it works for your consideration. If you live where the winter weather gets way below zero pure glycols get thick and gooey which is in opposition to a pumpable fluid so you certainly need to consider your environment if nothing else.

Bogie
 

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Thanks for the replies. Now that we are talking about accelerated where due to the lack of effective heat, my current 355 has a 180 degree thermostat, but doesn’t get above 155ish. Any idea why that would be?
That would be an overly large radiator for the BTU’s delivered to it. Or a system that is bypassing coolant.

The latter can be a leak past the thermostat which could include the heater bypass combined with too much BTU capability of the radiator. This is pretty common on big rig trucks hence seeing air shutters on the radiator or sections blocked off with cardboard.

A third option is a lying temperature gauge.

Bogie
 

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Discussion Starter · #11 ·
That would be an overly large radiator for the BTU’s delivered to it. Or a system that is bypassing coolant.

The latter can be a leak past the thermostat which could include the heater bypass combined with too much BTU capability of the radiator. This is pretty common on big rig trucks hence seeing air shutters on the radiator or sections blocked off with cardboard.

A third option is a lying temperature gauge.

Bogie
Stock radiator, I’m thinking it’s possible I got a coolant temp sensor that isn’t compatible/accurate with the temp gauge. I’m going to put an IR temp gauge on it when I get to work tomorrow.

Do you mind expanding a little more on how too cool of an engine can affect engine performance and wear? Why would that happen. Unburnt fuel causing west on pistons rings? How much performance loss can really happen for a 20-30 degree difference?
 

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Or maybe a bad thermostat. Put it in cold water in a pot on a stove. Put a meat thermometer in the water and turn on the heat. Note the temp at which the thermostat STARTS to OPEN. A 180 thermostat should start to open at very close to 180 degrees F. I think we can all agree that 155 is way too cold without all the verbal BS.
 

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Just because your test thermometer came out of the kitchen certainly doesn't make it more or less accurate then any other means of measurement . My temp gauge spikes at 195° before the t-stat opens initially , it reads 175 ° hot & running , stat is allegedly180° , ,my IR gun reads 182° ,, the barbecue meat probe type reads 185° , which one is " right" ? Your guess is as good as mine ....
 

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Yeah keeping the castings wet is vital to their survival, this is to a point more important than coolant temperature. As long as your able to hold off nucleate boiling the castings can be pushed well towards 300F.

In an engine there are hot spots that well the exceed the boiling point of most coolants. These rather obviously are exhaust valve seats and spark plug bosses. So when coolant temps get high these are the first places where it is likely that the coolant will locally boil even when the bulk coolant temp may be comfortably lower than its boiling point. When local boiling occurs then essentially the hot spot causing the boiling is dry and is free to enjoy temperature excursions to wherever the incoming heat energy will take it. Within a casting this excursion causes that metal to expand more than wetted cooler metal adjacent to the overheating hot spot. The end result when the forces exceed the strength of the material is you get a crack.

The reason for maintaining a pressurized cooling system is to hopefully keep these hot spots wet thusly transfering heat to the coolant which is the only chance of preventing a runaway hot spot in the casting surrounded by cooler metal.

Another way is waterless which when the curtain is pulled aside is essentially pure antifreeze of some sort which usually be mixtures of ethylene and propylene glycols. These have much higher boiling points well into the range of 350F at normal atmospheric pressure. The down side is they move less heat per unit volume so a cooling system sized for a 50/50 mix of water and glycol will stabilize at a temperature about 20 to 30 degrees higher. However, the advantage is that the hot spots have the potential at least to stay wetted without resorting to high pressure cooling systems. To a great extent this knocks down transient cooling system voltages that encourage corrosion between dissimilar metals. So this reduces to eliminates rust formation which has two major problems in a cooling system: first, rust is an insulator so once forming the heat transfer of the rusting surface goes down leading to that surface operating hotter or in a radiators tubes reduces heat transfer to the atmosphere; second, rust collects to plug passages starving those areas of surface wetness which leads them to local overheating. The big downside to waterless is it is flammable and slippery so most race venues ban its use which may well extend to water mixes as well.

I’m not selling the idea of waterless, although I use it, but I’m juxtaposing the difference in how it works for your consideration. If you live where the winter weather gets way below zero pure glycols get thick and gooey which is in opposition to a pumpable fluid so you certainly need to consider your environment if nothing else.

Bogie
Exactly. I ran Evans NPG for a while in a tow pig. I installed an oil temp gauge and an oil cooler to make sure the oil wasn't getting too hot, but that rig frequently saw coolant at 290 degrees with a 2psi radiator cap and never boiled, never had detonation, and never had a single cooling issue. As long as it doesn't boil, the coolant can still accept heat at the same rate and shed it at the same rate.

As you pointed out - straight glycols are slower to accept and reject the heat, so there are trade-offs.

The key is not the temperature as much as it is preventing boiling. A regular cooling system uses pressure and solutes to prevent it. But the actual temperature is pretty inconsequential when it comes to preventing overheating. The sweet spot is to make sure things get UP to a healthy temp without going BEYOND boiling temperatures.

Think of it like moving rocks in a wheelbarrow. Your job is to move the rocks from A to B as someone adds new rocks to A. Rocks are heat, the wheelbarrow is the cooling system and the size of the pile is temperature. You can accomplish the same task by putting a few rocks in the bucket and making several quick trips, or loading the bucket full and making fewer trips. The secret is to not let the A pile get bigger. If you're moving too slowly (not having the capacity to move rocks faster than they're placed on pile A), the first pile gets bigger (higher temperature).
 

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Stock radiator, I’m thinking it’s possible I got a coolant temp sensor that isn’t compatible/accurate with the temp gauge. I’m going to put an IR temp gauge on it when I get to work tomorrow.

Do you mind expanding a little more on how too cool of an engine can affect engine performance and wear? Why would that happen. Unburnt fuel causing west on pistons rings? How much performance loss can really happen for a 20-30 degree difference?
This goes back to several things like the always problems of getting consistent cylinder to cylinder mixture ratios with a carb or TBI which in turn produces rich to lean running cylinders which further results in differing power output by cylinder which results in
in uneven twist moments in the crankshaft.

I have always been amazed at the cylinder to cylinder deviations of mixture that are seen with carburetors and TBI where manifold runners feed from a plenum. This is largely a precipitation, condensation, and inertia problem.

Precipitation and condensation I put as close results but different from functions as relatives where fuel in the mixture can change from true gas to liquid or from a mist to pools for changes in temperature, pressure, velocity and inertia as the mixture flows from boost venturi or injector nozzle into a centralized plenum and runner system. Neither a carburetor nor high or low pressure a TBI are delivering fuel in a gaseous state. That being a mist from globules to finely divided spray but nonetheless the physical state is that of a liquid, there has not been a change to a gaseous state. I mean you have to consider if there is it is only partial quantity state change. Further with pressure and temperature fluctuation within the manifold the physical state of the fuel can flip back and forth between a true gas and a liquid. From a max power standpoint a finely divided mist in a liquid state is better that a change to a true gas simply because a true gas is quite expanded in volume therefore the density is greatly reduced and power with it. Insofar as the fuel in a liquid state in concerned colder allows a denser packing of the molecules thus a greater quantity of molecules per unit volume where again this can allow greater cylinder packing and more power output. But there are temperature, pressure, velocity, and inertia changes that can flip these states back and forth.

To a great extent I’m going to separate out inertia in that changes in direction of a mixture of differing weight molecules is going to throw the heavier molecules to the outside of any turn. Now turns can be useful in stirring the mixture as well so velocity of the mixture and abruptness of the turn counts for a lot. Going to an extreme was the Ford Y-block and its H shaped intake that stacked the runners. This was made to stir the mixture to provide more homogeneity cylinder to cylinder. The problem got into stirring also causes separation by molecular weight as velocities go up as well as results in short side flow separations from the wall which reduces the functional area of the port to something less than the calculated area. You can see this effect in SBC head flows where there usually is a large drop in flow and the increase of flow amount right around .5 inch. I this case what we see is the port floor flow stops making the abrupt turn into the valve pocket but rather starts across the pocket above the intake valve, this reduces the flow area and essentially throttles the port. If you understand what flow for lift numbers are telling you as an example I would propose that if you are on a budget and had selected ProComp heads which flow so-so at low and mid lifts but come on gang busters at and over .5 inch lift; then you should rethink the cam and valve train that chases this piece of important information rather than using a lower lifting cam identical with a head selection that runs out of breath around .5 inch. I’m actually thinking about a you tube test with Richard Holdener where he compares performance from a ProComp headed SBC to I think are AFR’s if my crappy memory holds. The power differential is considerable for an identical short block. In the real world if I was going after a certain power target, I go at the cam and valve train between these a lot differently.

Now the way the production manufacturers have approached these carb and TBI problems in the past has been with smaller ports to get the velocities up to reduce fuel condensation and resultant pooling, added exhaust heat to force boil off pooled and condensed fuel, and to force a state change to a true gas which is a more consistent burner and easier to light off in the cylinder. None of this enhances top end power.

Now modern heads are largely designed to do all the fuel mixing within the cylinder where with port injection depending on the injector timing may enter the cylinder from a poop of liquid sitting on the backside of the valve to a finely divided but wet spray. So the shapes of the combustion chamber are used to perform the various acts needed to make a combustible mixture. For guys running a more old fashion carburetor these heads allow the use of larger ports and valves with an unheated intake as any wet fuel entering as with port injection will get mixed into a combustible jumble inside the cylinder. Now this doesn’t fix the inherent cylinder to cylinder AFR’s that happen for a long list of reasons. But it goes a long ways to using the energy of the delivered mixture by insuring that what can be burned is burned.

Believe me this long submission is nothing more than skipping stones across the subject.

Ain’t grammar or spell checking this for time reasons, sorry. Bogie
 

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Do you mind expanding a little more on how too cool of an engine can affect engine performance and wear? Why would that happen. Unburnt fuel causing west on pistons rings? How much performance loss can really happen for a 20-30 degree difference?
I've seen bore wear graphs...the curve goes nearly vertical below 160° and isn't really good until you reach 180°, with 200-205°+ being best for minimal wear. Until the engine is good and warm, the oil isn't at the proper temp to provide the best protection as it was designed,

Most of the raeson a 100, 000 mile mid 1980's or later engine is just frequently seen with great bore finish still visible is cold start mixture distribution, which a choked carb is terrible at really....a 100,000 mile 1960's or 1970's engine will be flat worn out, needing a bore job. All those coldcarbed sterts just eat it up.The OEM move to fuel injection greatly increased engine life due to more precise cold start mixture control.
The second important factor in engine wear improvement was closer tolerance fit and the move to lighter oils, which flow easier and sooner, not being so reliant on engine heat to get it thinned out enough to work in it's proper fluid state.
 

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An old time hot rodder friend believed that anything over 160 was over heating. Burney would spend countless hours and dollars making sure his cars never "over heated". My personal opinion on this is keep it hot. If it ain't losing water it ain't over heating. Those engineers are paid a butt load of money to figure this stuff out, might be we should listen carefully?
 

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An old time hot rodder friend believed that anything over 160 was over heating. Burney would spend countless hours and dollars making sure his cars never "over heated". My personal opinion on this is keep it hot. If it ain't losing water it ain't over heating. Those engineers are paid a butt load of money to figure this stuff out, might be we should listen carefully?
Agreed. Mineral oil is fine to 230, most synthetics are good to 260 or more, and a 2500-degree combustion event doesn't care if the water is 150 or 250 degrees. People always chase the thermostat temperature as a solution. What really needs to happen is for the oil temp to be correct (200-210), then choose a coolant ratio and radiator cap pressure (and radiator size) that will prevent boiling. We tend to translate that to mean all engines are best at X degrees, but the truth is, every engine, cam choice, engine bay, and even something as insignificant as an oil pan or intake means that every single engine is technically different.

I had a Caddy 500 with non-aqueous coolant and frequently saw 290 degrees, but the oil stayed just fine. One time I saw the oil temps get to 230 and that was towing 10k lbs from Phoenix to Albequerque in July. 150 miles of non-stop uphill with my foot to the floor. The first time I did that, it was so strange to watch the coolant gauge peg in the red and I just kept my foot on the floor.
 

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We don't even put temp guages in our race cars anymore. I don't care what the water temp is, as long as as it has water. We use a cooling system pressure guage instead and a cap that doesn't have a relief valve. I do have a oil temp guage however. It's set at 280' to turn on the light.
 
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