The cooling system of an engine is the conduit through which heat flows from the mass of the engine to the ambient air. Ideally, an engine would achieve optimal temperature and then gain no additional heat. Heat from combustion would remain within the combustion chamber and would not transfer to the heads, block, etc. Of course, this isn’t what happens. An engine gains heat, which will raise its temperature far above optimal, high enough to damage it. This heat must be removed, which is exactly what the cooling system does.
Like most things automotive, the cooling systems in our vehicles has seen an evolutionary process toward more complexity and effectiveness.
Persistent Misconception
You do not want your car’s engine to run as cool as possible. Not at all! Consider the following, the gist of which was voiced by the super race mechanic Smokey Yunick.
Basically, an engine generates heat, and it’s this heat that produces the air expansion that performs work. Ideally, all of the heat would stay in the combustion chamber where it could do work. Any heat that escapes (to block, heads, cooling system, etc.) can’t do work. Simple enough, right?
Two objects of different temperatures and in contact with one another will transfer heat from the hotter to the cooler at a rate that depends on the temperature difference. The greater the difference, the greater the heat transfer.
If we take this further, we could say that if the engine were at the temperature of the combustion chamber (it can’t be), there would be zero heat transfer from the combustion chamber to the rest of the engine! All of the combustion chamber heat would produce work!
Taking this principle and putting it into realistic practice would mean that you allow your engine to be as hot as possible without being overly hot, to keep as much heat in the combustion chamber as is possible. Don’t confuse this with the issue of the temperature of air that’s consumed by the engine. We want this air to be as cool as possible, since the cooler air is the denser it is. (See I Love Hood Scoops). With more (denser) air, we can mix more fuel and make more power, right? Another related factor is that we want our engine oil to get hot enough to purge itself of moisture that condenses in the crankcase.
The majority of early cars utilized a radiator but no water pump. This was the thermosyphon system, which used the water temperature differential to move water through the engine and radiator. Hot coolant would enter the top of the radiator and settle as it cooled. Cooler fluid would then be pushed into the engine from the bottom radiator hose, under force of the incoming hot coolant. The radiators were oriented vertically and were not yet of the horizontal, crossflow design. This cooling system design persisted on some models until at least the late ‘30’s. It obviously had severe limitations and was troublesome on hot days when the vehicle was moving slowly.
Early Ford Model T cars did have water pumps. These were eliminated and the system was converted to the thermosyphon type to reduce manufacturing costs!
Have You seen the Salt Box?
We may take for granted the substances we use for our modern cooling systems. The “50-50 antifreeze and water” is pretty much universal wisdom. However, it wasn’t always this way!
Prior to the late ‘30’s, there were a number of substances added to the water of a cooling system in order to keep the coolant from freezing. Of course, in areas where temperatures never dropped to freezing, most people used straight H2O. Substances that were used to prevent freezing included salt, calcium chloride, glycerin and kerosene. When it was discovered that methyl alcohol worked well, it became the go-to substance.
Both salt and alcohol will attack metal parts, and alcohol will evaporate. Those using alcohol had to ensure that the evaporation didn’t compromise the ability of the coolant to resist freezing.
Ethylene glycol was not a new substance when it started to be marketed as an anti-freeze in the 1920’s. It didn’t attack metal or evaporate, and was a good enough substance to still be in use almost 100 years later.
The substance was first developed in 1856, and was used in the production of dynamite, and later, as a precursor to polyester. Plastic soda and water bottles are made partly from ethylene glycol.
What might not be so well known is that water transfers heat much better than ethylene glycol or a mixture of water and ethylene glycol! If your engine never saw freezing temperatures, you could use straight water to good effect. That is, if water did not have the corrosive effect that it has! Even in the warmer climes where freezing is not a concern, you will want to add something to the water to prevent internal engine corrosion. For most people, that “something” is anti-freeze!
High Pressure, Man
Engine cooling systems are pressurized, with the spring in the radiator cap dictating the peak pressure. The main reason for this is that water, like many liquids we know, will only remain in its liquid state if under pressure. The water in the tea I’m presently drinking is under about 14.7 pounds per square inches of pressure, due to the atmosphere. If not for this pressure, it would boil away, even at the 68° F or so in this room.
It follows that if we subject water to a pressure that’s higher than atmospheric, it will boil at a higher temperature than the 212° F (100°C) we are used to. That is absolutely correct, and our 15lb. radiator cap will allow the coolant to reach about 250°F without boiling. Why is boiling to be avoided (unless you’re making tea)? Boiling coolant will not absorb any more heat and the steam that forms will not flow gracefully through the cooling system. This would be fatal to an engine.
This chart shows the relationship between atmospheric pressure and the boiling point of water. If you could create a vacuum that was 0.00005lb./in2, water would boil somewhere around -90° F.
Industrial machines as far back as the 19th century (the 1800’s, for those in Idaho) used the principle of superheated steam, achieved by heating water under pressure.
An example of the statement above is the Parson’s reaction turbine engine of the RMS Titanic. Each of the two 4-cylinder reciprocating steam engines fed exhaust steam to the turbine engine, which drove the center propeller. The turbine engine made about 16,000shp (shaft horsepower). The highest pressure in the system was found in the two high-pressure cylinders (one for each engine), and was 215psi at 394° F.
Here’s a drawing of the Titanic’s turbine engine. The red ovals indicate the turbine blades as seen edge-on. Quite a bit of interesting technology for over eleven decades ago!
Antifreeze
Ethylene Glycol
I have to admit that I never really respected the coolness of ethylene glycol. It’s some wild stuff, made by adding ethylene oxide to water:
C2H4O + H2O → HO−CH2CH2−OH Yes, it’s just carbon, hydrogen and oxygen. (That’s what carbohydrates are composed of.)
Pure ethylene glycol freezes at slightly below 10°F! Yeah, that’s only 22° below the freezing point of water! Ethylene glycol boils at 388°F, which is an advantage in cooling. However, it only transfers heat about half as well as pure water!
Ethylene glycol and water have an interesting interplay. The combination of ethylene glycol and water produces a substance that has cold-temperature characteristics much different than either substance alone. Adding water to ethylene glycol lowers it’s freezing point tremendously (which is good), while lowering its boiling point (which isn’t good), but to a lesser degree. Also, there’s nothing linear about the freezing and boiling points relative to mixture percentage.
A 60/40 antifreeze/water ratio will prevent freezing down to -63°F, while a 50/50 mixture will protect to -34°F. As the mixture gets closer to pure ethylene glycol, the freezing point rises to the above-mentioned 10°F.
If you were really interested in freezing protection as well as optimal cooling, a 50/50 mixture in winter will protect you to -34°F and switching to a 10/90 in summer will provide near optimal cooling, while retaining corrosion protection. There are anti-corrosion products that are sold to be added to pure water for best cooling. If you live where it doesn’t freeze, that might be the ticket.
Note that as the table progresses from 10/90 to 60/40, °C freezing point drops 50°C while boiling point rises 10°C. The boiling points shown are for atmospheric pressure, not the pressure the coolant will be under in your cooling system. Note that 60/40 is the highest recommended ratio of antifreeze/water.
This graph shows the interesting characteristic of the extreme non-linearity of antifreeze mixtures and their freezing temperatures. Who would think that if you mix (50/50) something that freezes at 32° F and a substance that freezes at -10° F, the combination would have a freezing point of roughly -40° F! The average of the two temperatures is about +11°, after all. Not that chemistry observes averages, but the behavior of the combination is not intuitive!
The boiling point versus mixture percentage is not linear but is certainly more so than the freezing point graph. It might seem straightforward enough to look at the two graphs and pick a mixture ratio for your location, particularly if you didn’t have to worry about freezing. This might be true, but the reduced ability of antifreeze to transfer heat relative to water is going to complicate the calculation.
Don’t Hurt the Critters!
Ethylene glycol is extremely toxic. The fact that it has a sweet taste makes it even more potentially hazardous. Animals will drink it if they come across it. It is biodegradable, so it may be safely disposed of by pouring into gravel or foliage. I’d water it in, if possible, to ensure traces aren’t left for animals to ingest. Never leave it in open containers. Ethylene glycol poisoning leads to a gruesome death — please be responsible with it. Also, always follow local regulations.
If you find a drop of something or other below your car, get a sample on your finger and look at it in good light. If I still can’t discern what it is, I’ll touch it to my tongue to see if it’s sweet. I’m talking about putting a miniscule amount on my tongue. This is enough to verify if it’s coolant or to eliminate it. I should say that if you do this in such a manner that it’s a problem, you might be an imbecile. I’ve never had a problem, since I’m not an imbecile. (Don’t ask my wife)
Propylene Glycol
This substance was developed primarily because ethylene glycol is so toxic. Its chemical formula is C3H8O2. Propylene glycol is considerably more viscous than ethylene glycol at low temperatures, and thus its use in industrial systems operating at temperatures of 0°F or below should be carefully reviewed with respect to pumping requirements.
This product biodegrades approximately as well as ethylene glycol, so it’s no better from an environmental perspective. I’d recommend it mainly for anyone concerned with accidental poisoning of animals. Ethylene glycol will perform somewhat better overall.
Freezing/Boiling values for two different mixtures of Propylene Glycol.
IATs, OATs and HOATs
Well, it couldn’t be as simple as Ethylene vs. Propylene, could it? Nope! The following information covers the types of antifreeze products that are manufactured presently. Unfortunately, it seems to be difficult to tell which products fit into exactly which categories. If you Google one of the terms, such as “IAT” and “antifreeze”, you can pull up various sites that sell these products and often provide the manufacturer’s information. An example is provided below.
- IAT Ethylene glycol is classified as an IAT, or Inorganic Acid Technology. is the traditional green colored antifreeze that is the closest formula to what antifreeze was prior to the 1980’s. The lifespan of traditional coolant is about three to five years. Most classic vehicles will use an IAT antifreeze.
- OAT Propylene glycol is an OAT, or Organic Acid Technology. It offers silicate-free protection of all metals, and for a longer period of time. The long life (LLC) or extended life (ELC) coolant has a service life of five years or 150,000 miles. Used by European automakers.
- HOAT This stands for Hybrid Organic Acid Technology. This formula is usually orange but can also be red or yellow. This formula is a mixture of IAT and OAT. The orange product (only) contains 10 percent recycled coolant. Like IAT, it contains silicate for aluminum protection. Provides longer protection than straight IAT antifreeze and is free of nitrite, phosphate and amines chemicals.
- SHOAT Silicate-Enhanced Hybrid Organic Acid Technology. Used by European automakers.
- SOAT Silicate-Enhanced Organic Acid Technology. Long-life coolant capable of providing antifreeze service life of five years, or 150,000 miles.
- POAT Phosphate Organic Acid Technology. Used by Asian automakers. Long-life coolant capable of providing antifreeze service life of seven years, or 250,000 miles.
This is the information provided by one website for Zerex 841943 – Zerex Pink Fully Formulated HD Antifreeze and Coolant
Brand: Zerex
Product Line: Zerex Pink Fully Formulated HD Antifreeze and Coolant
UPC: 028882683319
Volume: 1 gallon
Coolant Concentration: 50/50
Coolant Type: P-HOAT
You might spend some time on the web looking at some of the more off-the-beaten-path products that are available. One such manufacturers is Evans Waterless Engine Coolant.
DO NOT MIX TYPES OF ANTIFREEZE FAMILIES! THE RESULT CAN BE UNDESIRED CHEMICAL REACTIONS THAT RESULT IN PARTS OF THE COOLANT BECOMING NON-LIQUID!
Tap Water, Distilled Water, Perrier®, What Do I Use?
Most people don’t go to the trouble to use distilled water in their cooling systems. However, since this contains no minerals, it’s the best to use. If you have a new or newly rebuilt engine and a new radiator you should give this some thought. I’d skip the Perrier®, though.
Water Wetter Products
If you decide to run straight water in the summer for maximum cooling performance, here are some products you can add to the water that will provide the corrosion control that the antifreeze would otherwise provide.
Lucas Super Coolant
Red Line Water Wetter
Royal Purple Purple Ice Super Coolant
Water Wetter Super Coolant
Measuring Coolant Ratio
How do you know what the AF/water ratio is in your cooling system? Measure it, of course!
This Prestone tester has been the go-to product for decades. It’s inexpensive and accurate enough. I think I have about three of these, because when I try to find one, I can’t seem to be able to, and end up buying another! Later, when I’m not looking for one, I’ll come across the tester that I was earlier looking for and couldn’t find. (Yes, there are times that it’s hard to be me.)
This type of coolant tester is newer and fancier than the Prestone type. I don’t have one of this type, but I should get one, because, well, I don’t have one. And since I’m a guy, I need one!
Radiators
From the dawn of the auto industry up to the 1970’s, radiators were constructed from copper and brass. These two metals were resistant to corrosion and were very well suited to the purpose.
The changes of the 1970’s caused automakers to look for lighter, less expensive alternatives to copper and brass. This meant aluminum tubes and fins, and plastic side tanks. Aluminum is far more prone to form pinholes due to corrosion, while being more susceptible to corrosion in general.
The switch to aluminum and plastic was quite protracted, with the older (some would say ‘better’) materials continuing to be used for decades.
Radiators today are of the crossflow variety, with coolant flowing horizontally through them. There are three different basic designs: single pass, double pass and triple pass.
It certainly isn’t a matter of a triple pass being better than a double pass and a double pass being better than a single pass. As with everything else, there are trade-offs. With a double and triple pass, the coolant stays longer in the radiator, but the flow is more restricted. The double pass has both the inlet and outlet on the same side of the radiator, so that is a consideration if you’re considering replacing a single pass with a double pass.
I have seen some references to “coolant moving too quickly through a radiator”, which is absolutely not true and is not a consideration. Given the added flow restriction a triple pass radiator has over a single pass, if you installed one in place of your single pass, I would expect the coolant to move more slowly through the cooling system. However, the coolant would spend a longer time in the radiator, the latter offsetting the former. Sure, it’s actually a bit more complex than this, but don’t buy into bad science.
OEM radiators, like most original components, are intended to be adequate for the task. It’s sometimes hard to say how much margin has been designed in. If your engine is making substantially more power than stock, there’s no guarantee that your cooling system is going to be up to the task under all conditions.
Sometimes there’s talk about the number and types of tubes, as well as the fin density. Suffice to say that not enough fin area isn’t good, nor is too much, as it will inhibit the flow of air through the radiator.
Early radiators had round tubes, on which the fins were placed. This wasn’t optimal from a surface area standpoint, since this shape has the smallest surface area per volume. Less tube surface area means less area for the all-important cooling fins. This shape is the most resistant to deformation from pressure, though. Tubes today tend to be flattened oval shape.
In buying an aftermarket radiator, I’d recommend going with a name brand, ideally one that is guaranteed to fit your application. Rather than the number of cores (tubes), look for one that is as thick as will fit. You don’t need to go crazy with the absolute biggest radiator you can find, if a thinner one will still be more than adequate, unless you have some money burning a hole in your pocket.
Some quality radiator manufacturers:
- BeCool https://becool.com/
- Wizard Cooling https://wizardcooling.com/
- Griffin Radiator http://www.griffinrad.com/
- C&R Racing https://www.crracing.com/
- Cool Craft http://www.coolcraft.com/
- Entropy Radiator http://www.entropyrad.com/home.php
Aftermarket radiators vary in quality and price. The best are aluminum and are often thicker than a stock unit. I’d gladly replace a stock radiator that has plastic tanks with an all-aluminum one. You might run into a clearance issue, where you need to use extra slim electric fans. I’ve always felt that a performance radiator is money well spent, great insurance, and looks good to boot, even in a classic engine compartment. (Just leave those pink spark plug cables at home.)
A better radiator might have more fin area, but not to the extent of inhibiting air flow.
Tube configurations vary by cost and application. Tubes are never round, as a round tube has the minimum surface area relative to volume. We want just the opposite!
Radiator Caps
Radiator caps are usually 15 or 16psi but can range up to 30psi. In terms of pressure values, a higher value will allow higher pressurization of the cooling system suppressing any tendency of the coolant to boil. Your cooling system, including all hoses, must be able to handle the additional pressure! I wouldn’t recommend a higher psi cap unless there is a specific reason for it, and you are positive that your cooling system can handle the extra pressure. Even then, I would think that going from, say, 16 psi to 30 psi is looking for trouble.
Boiling point goes up approximately 3°F for each additional pound of pressure.
The only reason you would go to a higher psi cap is that your present cap is venting at high temperatures. If this is the case, you need to investigate why. Chances are that something is causing this and changing caps will, at best, mask the problem. On the other hand, if you have a monster of an engine and all of the necessary and recommended cooling system components (radiator, coolant, fans, fan temp sensor, water pump, etc.) are 100% verified and you have a venting problem only when it’s really hot, you might investigate a higher psi cap. Don’t treat this as a magic bullet for a cooling problem!
Some people switch to either 90/10 water/AF, or 100% water (with corrosion preventer) in the warmer months. To offset the tendency of the coolant to boil at a lower temperature (vs. 50/50) they use a higher psi radiator cap. As we’ve discussed, the 90% or 100% water will transfer heat better, due to the relative lack of ethylene glycol, which transfers heat much more poorly. Just don’t forget to change back in the fall, or you might have an embarrassing and expensive problem!
If you used a 60/40 mix in the Winter and then changed to a 90/10 ratio in the Summer, you could offset the lower boiling point by using a radiator cap that was rated 4 or 5 psi higher. This would increase your coolant mixtures heat transfer ability by 36% (70 to 95, ∆ = 36%). With 100°+ Summer temps, this could be a big advantage for a large engine.
More Than One Type
There are a few different types of radiator caps that you should know about. The first two are “full pressure” and “partial pressure” types. The full pressure type is probably the one you’re familiar with. This cap allows the cooling system to pressurize quickly and to then stay pressurized for quite some time after the car is parked. The partial pressure type has a valve that’s open and is only closed when the system builds up enough pressure. If it’s a cold day and maybe a shorter trip, the system may not pressurize. That’s okay, since it will pressurize when it needs to.
The best recommendation I’ve read is to stick with the type that came with the car. Of course, if you didn’t know there was more than one type, you might have unknowingly bought “the other type” to replace your failed factory cap. Not a big deal, but now you know!
Two of Both Types
- With lower seal only, free-hanging vent valve (Partial-pressure, open system)
- With lower and upper seals, free-hanging vent valve (Partial-pressure, coolant recovery system)
- With lower seal only, spring-loaded vent valve (Full-pressure, open system)
- With lower and upper seals, spring-loaded vent valve (Full-pressure, coolant recovery system)
Revisiting ‘The Cool Engine’
In the 1980’s, with the advent of fuel injected 302’s, 305’s and 350’s, there arose an aftermarket that catered to these owners by offering such things as lower-temp thermostats and ‘performance chips’. The performance chips are a different matter, but the lower-temp thermostats took advantage of a lack of knowledge among even experienced car enthusiasts. “Sure, I want my 5.0 Mustang to run cooler so it will make more power!” Pretty simple! And, false!
Earlier on this page we expressed the value of an engine that was hot, as long as it was not above its recommended operating temperature. To sum up: this lets more heat stay in the combustion chamber where it can produce power. While the average driver likely doesn’t know that their car makes more power on a cool day, the auto enthusiast is keenly aware of this fact as well as the reason behind it. I think this leads to a bit of a confusion when it comes to engine temperature, not air temperature. The aftermarket auto performance industry eagerly catered to this misconception in offering their ‘performance’ thermostats.
The engine thermostat exists to allow the engine to warm up as quickly as possible and to attain an operating temperature that is high enough to allow the engine to operate effectively. In doing this, it establishes a base temperature for the engine. The warmed-up engine will not go below this temperature.
This graph is somewhat idealistic but illustrates the differences between a 160° thermostat and a 180° thermostat in the same car, traveling the same route. You can see that the car starts cold, does in-town driving, then highway with a long uphill and downhill, then finally back in town. You can see how this represents the statement that the thermostat sets the base temperature, not the top temperature. Each thermostat opens at its design temperature, the 160° first. When opens, the engine temperature drops slightly for a short while.
The two graph lines are mostly overlaid, with the exception of the opening of the thermostats and the end of the downhill portion, where both temps go to their respective bases of 160° and 180°. The operation of a thermostat is somewhat more complex than this, as it’s not merely a matter of being ‘open’ or ‘closed’.
The thermostat should start to open at the rated temp, +/- 2° to 3°. It should fully open at about 10° above the rated temperature. As with any type of thermostat, there is a built-in hysteresis (histəˈrēsis). That is, the operating point with temp increasing is slightly different than the operating point with the temp decreasing. Your car’s fan thermostat and your home’s heating/AC thermostat have this same hysteresis.
“Why so?” you hear your inquisitive self asking. Well, I’ll tell you. If not for this effect, the thermostat would find itself constantly toggling at the breakpoint, which is now at the same temperature for the increasing and decreasing points of the graph. It would constantly be switching between ‘on’ and ‘off’. You might not notice this much with your cooling system thermostat, but you sure would with your fan thermostat, if your engine has an electric fan! It would be constantly on – off – on – off. The same for your home heating or cooling system, constantly on – off – on – off. Hysteresis is good; magnetic materials love it!
Using an Overflow Bottle (Don’t Leak in Public!)
If you are using an overflow container of some type (most of us are), you should be aware of the fact that this takes a different type of radiator cap. When the engine cools off, the lower pressure in the cooling system should now allow atmospheric pressure to push coolant from the overflow back into the radiator. To do this, there has to be a valve that is pushed open by the difference in pressure between the cooling system and atmosphere. That’s what makes a radiator cap that is suitable for this application. Beside not puking poisonous coolant all over the street, this action also purges air from the cooling system. In fact, if you’re not already using an overflow, you might question just what degree of mental impairment you might have, you Public Leaker!
Overflow containers weren’t all that prevalent in the 1960’s, with most engines venting coolant straight to the ground. Ford did have this iconic and cool bag that they used. It was typically found mounted on the fender liner.
When overflow tanks became mandatory, they were usually made of white, translucent plastic. The one shown here, for a ’68 – ’74 Chevy Nova, had a lightweight plastic cap that did not completely seal the container. Air could be forced out of the bottle when hot coolant was flowing into it.
Later model cooling systems might have a setup like this, where the overflow tank is pressurized along with the radiator. In this case, the ‘radiator cap’ is on the overflow and the radiator itself has none. This system, with the overflow being pressurized, is not strictly a replacement to the earlier non-pressurized overflow, merely a newer alternative to the pre-existing system.
This is an example of a simple little component that has caused many people much frustration. The thermostat exists to establish a minimum temperature for the cooling system and to allow the engine to come up to temperature quickly. It does this by closing off the radiator to coolant flow until it opens at its design temperature. The circulating coolant still provides the needed cooling for the engine, even prior to the thermostat opening.
The Ford Model T thermostat is a bit different than those we use today, no?
Here’s a Model A thermostat. It doesn’t quite look like eighty-year-old technology, does it?
An engine cooling system thermostat is a model of simplicity. There is a small cylinder filled with a wax that is formulated to melt and expand at a specific temperature. When this happens, the expanding wax pushes a shaft that opens the valve, which is usually (today) against the flow of coolant.
Note that it’s not just a matter of the thermostat being open or closed. If ambient temperatures are low, the thermostat will be partially open, allowing the needed amount of coolant to flow through the radiator without allowing so much that the coolant temperature drops below minimum. An engine needs heat to operate efficiently and there is such a thing as being “too cool”. The thermostat helps prevent this.
In the righthand image above the engine is cold and the thermostat is closed, keeping coolant from flowing through the radiator.
Thermostat Temperatures
Thermostat temperatures have varied in the past, as prevailing thoughts about optimal minimum engine temperatures changed. Generally, the range of temperatures varies from about 160°F to 205°F. Heat really isn’t the enemy of an engine, as long as it’s not excessive. The term “excessive” here means exceeding the capacity of your cooling system.
Beginning in the 1980’s, performance thermostats were sold as aftermarket performance parts. These usually had a temperature of 20°F or so below the stock unit.
I have to think that most people making use of these units were under the impression that this would allow their engine to operate cooler, and that this would be an advantage. All the lower temp unit does is establish a lower minimum engine temperature; it has no effect on overall engine temp or max engine temp. Even if it did, the premise is that a cooler engine is better, which is not true. As long as your engine is not overheating, it will be more efficient and make more power at higher temperatures.
Bleeding a Cooling System
This can be as easy as about anything can be, or it can kick you squarely in the butt. Water pumps can’t pump air, and you need to get the air out of the system. A lot of times this just amounts to putting some extra coolant in the overflow and then temperature cycling the engine a few times. When the engine cools, it will pull the coolant in from the overflow and displace the air. Your heater should be on during this process, since it carries coolant too.
Some vehicles have small ports which must be opened with the engine warm, to allow trapped air to be forced out. These are usually sealed with a small hex head bolt and are located at the high point(s) of the cooling system. Check your owner’s manual, Haynes, or factory service manual.
Symptoms of air trapped in the cooling system include a heater that is cold or lukewarm, the engine not cooling properly, and the indicated engine temperature being absurdly high or low. If there are no bleed ports and you’re 100% sure of this, just temperature cycle the engine a few times, waiting a few hours between cycles, the last one being overnight if possible. The engine doesn’t have to get hot, just warm enough for the thermostat to open.
Inconvenient Memories
Years ago, I had a fifteen-year-old car that was well used and a real pain to work on. The engine was fitted into the engine compartment with a shoehorn, I’m sure. I couldn’t get to anything easily. It had an issue in that it ate coolant, albeit fairly slowly. I got in the habit of putting in whatever I had handy, water or antifreeze. Well, I lost perspective on the actual nature of the coolant, whether it was cold hardy or not, and we had a real cold period. I was almost home, after driving ten miles from work, and the temperature maxed the gauge. Of course, it was also snowing, and I had the wrong shoes and just a light jacket, so I decided to run it the last mile or so and let whatever happened happen. The car survived but was later subject to my non-mechanical daughter driving it from school with the parking brake still on! I was told there were actual flames when she got home! Anyway, the car is gone, and I was never so glad to get rid of one in my life!
Radiator Fans
Prior to the appearance of the cool electric fans, there have been a handful of advances, particularly for the more performance-oriented engines.
This is a reproduction of a 1940’s fan. Nothing fancy here.
Here’s a late-’60’s Pontiac flex-fan. At high speeds the thin metal portion of each blade is forced close to flat by the airflow. Since high engine speed (usually) equates to high vehicle speed, this makes the fan less efficient, as it’s not needed as much. More importantly it reduces the power needed to drive the fan, thus reducing the power loss from moving air that’s not needed anyway.
This is a fan with a thermostatic element. When it’s colder, the thermostatic element ‘slips’ and the fan is driven at a lower speed. When air temperatures are higher, the thermostatic element will ‘lock’ and allow the fan to spin at a higher speed.
Wait… what’s with the oddly spaced fan bladed? The fan assembly is indeed balanced, as the blade spacing is chosen to not compromise that. However, the uneven spacing eliminates much of the harmonic noise that would otherwise be generated. I love engine noises, but I don’t think I particularly want to have the noise from my fan be a part of that symphony of sound.
Fan Shrouds
Even into the 1960’s not all cars used fan shrouds. Some shrouds were little more than open-ended plastic cylinders that looked like they had been cut from the middle of a barrel. The corners of the radiator weren’t even within the are of the shroud.
The shroud style below became the kind of basic shape, with one end rounded and the other squared. This was quite effective.
There were some cars, such as the first-generation Chevy Monte Carlo, that had enormously long hoods. This required a modified shroud to bridge the gap between the radiator and the fan, which was much larger than normal.
As with anything else related to automotive mechanics, treat your cooling system with intent and purpose. What’s the AF/water ratio in your cooling system now? How do you know?
Shroud Not Wanted
A high-output monster of an engine that intentionally does not have a fan shroud? What gives? The Chevrolet Corvette’s hot L-88 package (’68, ’69) was intended first and foremost for road racing. Heater? Nope. Radio? Nope. Air conditioning? Really? Power steering? Forget about it!
But why not a fan shroud, for goodness sake? Everyone knows a fan shroud increases the efficiency of the cooling system, right? This is true, under normal driving conditions. The L-88 Corvette wasn’t intended for normal driving! Far from it! It was determined that a shroud actually inhibits airflow and cooling under the conditions the L-88 was expected to see. Yeah, the Chevy guys knew what they were doing!
