The cooling system -- some detail

Master index
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Introduction
Parts of the cooling system as found on almost all water-cooled cars
Some very good links

Introduction (read this, it's important, really!)
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Internal combustion engines are inefficient. Well, at one time they were really inefficient, and now they're quite a lot less so, but they're still inefficient enough that they waste some of their energy making heat instead of forward motion.

Ideally, when you mix fuel and air together inside an engine and make it go bang, all of the air and fuel will end up making gases, gases that expand to a volume sufficient to make the car go to Wal-Mart for you. The Holy Grail is that combustion (the bang part) will be complete enough that only water and carbon dioxide are ultimately created, a goal that keeps emissions engineers awake at night. In practice, nobody's managed to get even close to that stage. Besides unwanted chemicals in the engine and exhaust, you also get...heat. Heat is a byproduct of that inefficiency we talked about earlier. Heat doesn't make your car go, it just makes it hot. In any engine made after about 1900, you get lots and lots of heat.

Well, if you leave that heat to build up, eventually the engine will lock up, or melt, or do something else expensive and otherwise not-nice. So we have to get rid of the excess heat and keep what's left to a manageable level. At the same time, the engine can't be allowed to run too cool, either, because it's designed to run within a specific temperature range. These are the reasons we need a cooling system.

Just so you have some idea of the kind of heat a cooling system needs to keep under control, consider this:
The thermostat is designed to keep the engine to about 90C / 194F.
Combustion chamber temperatures are about 850C to 1,100C, or 1,500F to 2,000F.
That's a lotta heat to get rid of.

The engine's own lubricating oil, exhaust system, spark plugs, the exterior surface of the engine and some other things are also involved in heat dissipation, but we're not concerned about them here.

In concept the cooling system is very simple. It works the very same way your body does when it sweats to get rid of excess heat: It takes heat from one place, and using a carrier of some sort, moves it to another, where it can be got rid of. Of course, if something goes wrong with this heat-getting-rid-of mechanism, you've got that expensive and not-nice thing happening to your motor. After this is where it gets complicated...

The parts and what they do:
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Coolant / Antifreeze
Engine water jacket
Head gasket
Water pump
Radiator
Radiator cap
Expansion tank/reservoir
Hoses
Thermostat
Radiator fan
Electronic controls

Coolant / Antifreeze back to top

The engine's innards are Swiss-cheesed with holes specifically designed to allow the flow of a liquid carrier that will absorb combustion heat and move it away from its source inside the engine. That carrier is the coolant, which also needs to double as an anti-freeze. If a glass bottle bursts when it freezes in a home freezer, you just know what freezing is going to do to your engine. So when your motor isn't actually running and generating heat, the coolant needs to stay liquid so as not to crack the engine in two overnight.

Coolant is equivalent to your body's sweat. But unlike your sweat, which carries heat away by evaporating (and you replace it by drinking more water), coolant is recirculated through the system continually, and offloads its heat through the radiator.

A chemical soup, coolant is. Its basic ingredient (besides water) is ethylene glycol, which is a sugar (yes, it tastes sweet). Ethylene glycol is a cheap, relatively stable, safe and efficient medium for the carriage of heat. As well, ethylene glycol's freezing point is very low when mixed with water. These properties make it an ideal base for automotive coolants. A nice technical link is available here.

Combined with the glycol are various corrosion inhibitors, lubricants and stabilizers. The details of those are not really important right now, but I should point out two things:

Plain water or undiluted coolant are very bad things to put in your engine. Normally the system should be filled with a 50/50 or 60/40 mix of coolant and distilled water. Honda now sells a ready-made premix that can be added straight from the bottle. Other brands will usually need diluting with distilled or de-ionized water in the correct proportions.
In warm climates where the temperature never ever gets down to freezing, plain water is OK provided it's supplemented with an anti-corrosion additive. Plain water actually has better heat-transfer characteristics than water mixed with antifreeze, even though antifreeze raises the fluid's boiling point. Believe it or not.

The only real cure for coolant problems is to change the coolant. If it's really old, brown and/or goopy, you will need to have a professional flush done to make sure you get all the deposits out of the block and radiator, and even then there is danger of internal corrosion. If the coolant still has some color in it, you can just drain, flush with a garden hose, then refill with fresh Honda premix.

Even more detail if you feel like reading it:

Coolant does get old, and when it does, it turns corrosive. The inhibitors that are normally part of the coolant become depleted, causing the pH to shift towards acidity, which starts corrosion. The effects of corrosion cannot be understated. Corrosion will attack your head gasket, the head and block mating surfaces, and the water pump. It will fill the system with rust, gel, silt and scale, and impair its ability to transfer heat. The preferred coolant change interval is generally two years. Long-life coolant, including Honda's own, are supposed to be good for five years, but most techs I've spoken to say to change it every two years anyway.

One way of telling how good your coolant still is, are coolant test strips that test for "Reserve Alkalinity". I used to have a link to a site that sold these strips, but they seem to have taken it down. Use a search engine.

Aftermarket "Long-Life" coolants are either green, red or pink. Honda's own coolant is a clear, dark blue. If you remove the rad cap (engine cold!) and look inside, you should be able to clearly see the openings of the radiator's tubes, and the fluid should be obviously one of the above colors. If the fluid is murky and the tubes are not visible, or if the fluid is brown, you've got problems: that fluid is OLD. Change it NOW! And don't mix different types of Long-Life coolant. While they may be "compatible", the additives in them may not be. If they aren't, they will reduce corrosion protection to the baseline 2-years.
A good link that shows which coolants are compatible:
http://www.eetcorp.com/antifreeze/Coolants_matrix.pdf

The preferred and recommended coolant for use in your Honda is Honda's own premixed coolant.
I do not know who makes it, but I do know it's the very best thing to use. If you balk at spending an extra ten or twenty bucks to safeguard your multi-thousand dollar expenditure ("but it's the principle of the thing!)", then that's your choice. If you make that choice, then let the following be your guide:
The use of inexpensive aftermarket coolants containing silicates (they're cloudy) is definitely NOT recommended. For corrosion prevention they're OK, but your water pump is under your timing belt. Silica is an abrasive, and it eats rubber water pump seals for lunch. Since you have to remove the timing belt to get at the water pump, $200 is an awful lot of money to spend just to cure a coolant leak when $10 would have prevented it..

The use of ordinary tap water for dilution of aftermarket coolants is also NOT recommended. Tap water can contain elements and compounds that your cooling system will not like. Your municipality may claim you have "soft" water, but you'd be surprised how quickly your rad tubes will get clogged by mineral deposits from that "soft" water. Use only distilled on de-ionized water when diluting aftermarket coolants.

If you do decide to use an aftermarket coolant, use something that's labeled as "Long-Life", and is borate and silicate-free. Dilute it 50/50 with distilled or de-ionized water. And change it every TWO years.

Engine water jacket back to top

"Water jacket" is the fancy name for the Swiss-cheesing mentioned above. The cylinders are clamped top-and-bottom by the head and the block, with their middles exposed. When a girl wears a short blouse, her bellybutton gets cold as air cools her tummy. When coolant flows past the cylinders' tummies, it does the same thing.

The head is also Swiss-cheesed with holes, both for coolant circulation and for oil drainage. The combustion chamber and exhaust valves (where most of the heat is) are both located in the head, so it's critically important that heat removal be efficient in this area.

Coolant enters the water jacket in the block at one end of the engine, and exits out the head at the other end, so you get a through-and-up movement of coolant, which is the direction the heat will want to take anyway.

It goes bad through corrosion, and (unless frozen) ALWAYS because of corrosion somewhere in the system. The use of silicated coolants can cause silting, which impairs coolant flow and heat transfer. Don't use the cloudy kind of coolant.

If corrosion has started, there is a chance you've got rust at the tops of the cylinder bores where they meet the heat gasket. That can render an engine uneconomical to fix if advanced enough.

The best way to preserve this component is to change the coolant as stated above. If silted/gooped up, a professional flush is necessary.

There are rare instances where the block casting is defective and porous. In those cases, the symptoms will be very similar to a blown head gasket. The difference is that this will show up very early in a car's life, like in the first month or so, early enough that it falls easily under the new-car warranty and will cost you nothing to get fixed.

Engine head gasket back to top

You wouldn't think this is part of the cooling system, and technically it's not. However...

The head gasket's job is severalfold. It keeps:
1) the combustion chambers and cylinders tightly sealed to each other;
2) lubricating oil out of the combustion chamber and the coolant;
3) coolant out of the combustion chamber and the oil;
4) oil and coolant from leaking down the side of the block to drip on the road.

Since the head gasket is the demarcation between the Swiss-cheesing in the block and the Swiss-cheesing in the head, and since it needs to hold pressure yet allow coolant to flow between one cheese-hole and the other without escaping or colliding with oil, this skinny component is very much part of the cooling system's sealing mechanism. When it fails, all sorts of awful things happen, particularly a reduction in the thickness of your wallet.

When coolant gets into the oil and the combustion chamber, it typically does so through a failed head gasket. It can do a lot of damage very quickly and destroy an engine in jig time. Age, corrosion and overheating are the main causes of head gasket failure.

If you have a failure of some other component, and your car overheated to the point where the gauge needle was in the red, you've run the risk of head and/or block warpage. If warpage has occurred, the head gasket will eventually start leaking.

Many (if not most) Honda gaskets are all-steel. If the head or block corrodes due to old coolant, it will be more difficult for them to clamp the gasket properly between them, and the immense pressures inside the the combustion chamber will eventually force a hole to form.

When coolant gets into the oil and the combustion chamber, it typically does so through a failed head gasket. It can do a lot of damage very quickly and destroy an engine in jig time.

There's no cure other than replacement. And that's very expensive.

You can prolong your head gasket's life through timely maintenance and keeping a constant eye on the temperature gauge, never allowing the needle to get into the red.

Water pump back to top

In order for the coolant to carry away heat from the engine, it has to be able to move, otherwise it'll just sit there getting hotter and hotter until it boils and your motor gets pooched.

Engines made prior to about 1920 usually had no water pumps at all (or thermostats, for that matter). They relied on a phenomenon known as "thermosyphon". A thermosyphon system relies on rising heat to create circulation, so heated water would rise out of the head, into the top of the radiator, and cooled water would fall down the rad and get sucked into the block again. This system worked after a fashion, but it was notoriously unreliable, especially on hot days, and was wholly inadequate as engines became more powerful and generated even more heat.

In modern engines, the water pump forces the coolant to circulate. It's installed on the engine itself. (As an aside, some very old forced-circulation engines, like the 1932-'53 Ford flathead V8 had two water pumps, one for each head.)

The water pump doesn't work like a bicycle pump or anything, all it does is spin around. It's called a "vane-type" pump. The impeller's vanes are angled such that when the pump spins, fluid is forced to travel in only one direction. Courtesy of Mista B0ne, a very knowledgeable and frequent poster to the Usenet group rec.autos.makers.honda, comes this photograph:
Water pumps.

The photo shows the business end, the one that meets the coolant. The other end (on a Honda) usually has a cogged wheel that engages the timing belt, which is what makes it spin. This cogged wheel is shown in the diagram to the right. The pump on the left in the photo is a new pump. You can clearly see the gold-colored impeller. The right pump's impeller was destroyed by corrosion.

Aftermarket pumps can have a defect that result in bubbles in the cooling system, an issue confusingly similar to a failed head gasket. The cooling system has a suction side and a pressure side. The water pump is the demarcation point between the two sides and in fact creates that pressure differential as it spins. If the water pump's shaft seals have gone bad, it is possible for air to be sucked in past the shaft seals and get mixed with the pressurized coolant being pushed through the block. You'll see that as air in the rad, and as a possibly elevated expansion reservoir level -- or foam in the reservoir -- along with a low rad level. Honda OEM pumps combined with proper maintenance never have this problem.

Radiator back to top

The radiator is probably the most well-known of any part in the cooling system. It's right up front, big, square, and sports a cap that spews scalding liquid if removed when the engine is hot.

To engineers, the rad is known as a heat exchanger. That means it's a device that moves heat from one system to another. In this case, it moves heat from the coolant in the cooling system to the air in the atmosphere. A fan attached to the rad helps pull air though it to aid in heat transfer.

The rad is very simple. It consists of two tanks, usually at the top and bottom, and a rectangular gridwork panel of thin tubes with delicate fins between them (called the core). Coolant enters the top tank, spreads out to go down all the tubes, cooling off as it goes, until it ends up in the bottom tank, ready to go back into the engine again. It's that gridwork of tubes and zig-zaggy fins that actually does the heat transfer from water to the air.

Hondas and most other modern cars use a low-volume, high-flow, low heat-transfer cooling system. What this means is that the cooling fluid spends very little time in the rad and sheds very little heat while it's in there. Thermodynamically, heat transfer is most efficient when there is the greatest possible differential between the heat source (the coolant) and its receiving medium (the air). For this reason it is desirable to keep the rad as hot as possible as it functions. If more cooling is needed, more of the surface of the rad ends up getting closer to the maximum temperature, and more heat is thus transferred. The upshot of all this is that the modern cooling system is extremely dependent on unimpeded fluid flow, of both water and air, in order to keep the engine at its design temperature, so proper maintenance is critical.

When people remove their thermostats in a misguided attempt at curing an overheating problem, they forget that engines do not produce the same amount of heat all the time. Removal of the thermostat causes overcooling, not overheating. This is unrelated to the "high flow, low heat-transfer" idea I mentioned above. You need to restrict coolant flow (with the thermostat) so heat can build up to the correct level, then you rely on "high flow, low heat-transfer" to maintain the desired temperature.

I have found that radiators are one of those very few parts that it is worth buying in the aftermarket rather than spending huge dollars for Genuine Honda. From Valeo to Visteon to several others, there are plenty of very decent aftermarket rads available for your Honda.

Finally, you've also got a teeny-tiny radiator hidden inside your passenger compartment, and some of the coolant circulates through it. That's your heater core, the thing that keeps your toes warm and windshield clear in the winter. Engine heat may be a sign of inefficiency, but it does provide a convenient way of warming you up as you drive on cold days.

Radiator cap back to top

Very small, very neglected, but very important! This tiny part doesn't just plug up the hole you used to put coolant into the rad, it also controls the amount of pressure the system is under. It's located at the highest point in the system, which is usually (but not always!) the top of the radiator. The cap contains two valves: One to release excess pressure, and one to allow negative pressure (vacuum) to be relieved. Plus it has a master seal against the top of the rad filler neck.

Water boils at 212F or 100C at sea level, and at even higher temperatures under higher pressures. The coolant itself raises the boiling temperature a bit, and the cap is what allows the system to run at a pressure high enough to allow the coolant to absorb even more heat without boiling.

Caps are rated for the pressure they hold. OEM Honda caps are made by Denso (ND), and are stamped "0.9" (13psi), or "1.1" (16psi), and may have different neck diameters, too. Make sure your car has the correct rated cap. Below are photos of OEM Toyota and Honda caps. The Honda one (for my Integra) is on the right. They're identical, but the Toyota one was about half the price (don't tell anybody! ^.^)

When things heat up, they expand, when they cool, they shrink. Coolant also behaves this way. Old-style cooling systems were designed to have a bit of air in the top of the radiator. That was done in order to give the coolant a place to expand into without spilling all over the ground.

Modern cooling systems have no air; coolant comes right up to the bottom of the rad cap. When the liquid heats up, expands, and pressure begins to build, one of the valves in the rad cap opens to allow some coolant to flow to the expansion tank, but only enough to reduce the pressure to a specified value, then it closes again. As the engine cools after you shut it off, the coolant starts to contract, and the coolant that was pushed out when hot has to come back in again, so the second valve in the cap opens to allow it back in. You've probably noticed that your expansion tank's level rises when the car gets hot, then falls again once the car cools off. That's why. If it doesn't go back down again, that's a danger sign! Often means a failed head gasket or a leak in the system.

A twist to the above: The newest rad caps don't even hold pressure all the time any more, only when the coolant starts to boil. You may find that even when full-warm, your rad hoses are still squeezy, as though the car were cold. Should the coolant start to boil, pressure will build very quickly, and that's when the cap starts holding pressure and the hoses firm up. You can tell this type of cap by turning it upside down and wiggling the stem that has the gaskets. If the stem is firmly attached to the cap, you have a cap that's supposed to hold pressure all the time. If the stem is very wiggly on the cap, you have the newer type. They're interchangeable, so you can buy whichever one you like.

If the cap is gummed up with cruddy deposits or corrosion from a neglected cooling system, it will not function properly, leading to possible overheating, and foam in the expansion reservoir. It is a superb idea to consider rad caps as consumables, and replace then every four or five years (with new OEM!) as a matter of course.

Expansion tank (AKA "overflow reservoir") back to top

This thing is just a plastic bottle that's hung near the top of the rad, saddlebag-style. It's where the coolant goes that was pushed out of the rad when the rad got hot. There needs to be a certain amount of coolant in it as priming fluid to make sure the tube on the cap is always immersed in fluid, so air doesn't get sucked in by mistake. Check the side of it for MIN and MAX markings. The MIN mark is more important, but slightly exceeding the MAX mark is not a problem.

A rubber tube goes to it from the rad filler neck, just below the rad cap. The important thing here, besides making sure the bottle doesn't leak, is that the rubber tube is attached firmly at both ends and is not split or deteriorated. If it's not properly attached or has a hole in it, fluid pushed out of the rad will get pushed straight onto the road, and you'll just suck air into the rad when it cools off. Air in your cooling system is a Bad Thing (I said that once before, didn't I?).

Hoses    back to top

The engine, radiator and heater core are mounted separately from each other, yet share the same coolant. The hoses connect the engine, rad and heater core together, so coolant can flow properly in and out without dribbling on your driveway.

Big fat hoses connect the rad to the engine. They have to be big to handle the volume that has to pass through them as the engine runs. Skinny hoses carry smaller amounts of coolant to the heater core, and to other parts of the engine that can benefit from engine heat, such as the throttle body, Idle Air Control valve, and intake manifold.

Hoses get old. When they do, they can leak (really badly). Coolant can't carry much engine heat if it's sprayed itself all over the road, so those hoses are pretty important. The big ones are the weakest, normally fail first, and fail catastrophically. A burst hose is a stranding occurrence: Your car--and you--are going nowhere until it's fixed and fresh coolant is put back in. And that's assuming you stopped before the engine wrecked itself on account of not being able to get rid of its excess heat. You were keeping an eye on the temperature gauge, weren't you? The smaller hoses generally don't split open in a disastrous manner like the big hoses. Instead they tend to develop small leaks--often due to overtightening the clamps-- that make a big mess in the engine bay from coolant spray.

Thermostat    back to top

In your house, you have a device of this name. Its job is to make the furnace heat the house to a predetermined temperature, then shut the furnace off. The one in your car is just like that, except you have no control over how it behaves.

A thermostat opens up when it gets hot, opening varying amounts depending on the coolant temperature it sees. The temperature that the thermostat begins to open is called the thermostat's rating. Honda OEM thermostats are rated at 78deg C, or 172deg F. Honda thermostats are fully open at 90C, or 194F.

The thermostat by default is closed. When it is, coolant can't flow to or from the rad. There IS recirculatory coolant flow from the water pump to the block when the thermostat is closed, through the thermostat housing's "bypass" orifice, which is only open when the thermostat is not. Fluid flow passes by the thermostat's sensing bulb. This is critically important. This system loop makes certain the block temperature stays evenly distributed, and that the thermostat always knows what the block temperature is. Once the block temperature reaches 78C, the thermostat begins to open up, slowly closing the bypass, so the fluid circuit now includes the rad. The "bypass" is fully closed at 90C, so all fluid flow then goes through the rad instead of being recirculated through the block.

The heater core is part of the "closed thermostat" loop along with block and water pump. This is so you can have almost immediate heat, and help defrosting your windshield on winter mornings.

This is the operational cycle for newer Hondas (roughly 1990 and up):
1) Coolant in the block reaches 78C (172F), thermostat begins to open up, unblocking the coolant passage from the rad
2) Water pump can now suck cool coolant from the rad through the thermostat in the lower rad hose
3) Water pump pushes this cooled coolant through the block
4) Hot coolant is forced to vacate, and is pushed into the rad through the upper rad hose
5) As the cooled coolant flows through the thermostat, it gets cold and closes up a bit, restricting flow again
6) Repeat from #1 until the system is all at 90C, at which point the thermostat stays open all the way.

It used to be common practice in the old days, when cooling systems weren't as efficient as they are today (and when emissions laws were a lot laxer), to install a different rating of thermostat in the summer and winter. You might install a 160F for summer and a 180F for winter. Don't do this with your Honda if original spec was 78C (172F). Forcing the engine to run cooler than it was designed for lowers fuel economy, increases wear, and can affect hydrocarbon emissions and cause you to fail emissions tests.

And by the way, some people have this idea that they can bypass cooling problems by removing the thermostat. This is dumb. Honda engines are designed to run with the cooling system at 194deg. Removal of the thermostat will cause the engine to run cold all the time, and so will you if it's winter when this happens. Brrrr.

Radiator fan    back to top

This part forces us to backtrack a bit, to the radiator.

The rad, being a heat exchanger, is dependent on there being a difference between the heat inside of itself and the heat outside of itself. The less difference, the less heat is transferred. For maximum cooling, the air immediately in contact with the rad needs to be changed as it heats up. If your car were always in motion, the very act of pushing the car down the road would be enough to keep the rad supplied with fresh, cool air.

Unfortunately, reality rears its proverbially ugly head, and heavy traffic interferes with our dreams of motive freedom. Here we are, stuck in traffic, idling away, inching ahead every so often. A modern Japanese cooling system and rad in good shape can cope with about 4 or 5 minutes of this. By that point, the rad has become saturated with heat, the air surrounding the rad matches the rad's temperature, heat exchanging stalls and the temperature gauge begins to climb.

So what to do? You can honk your horn, but that won't make the traffic ahead go away. We can't make your car move, but we can make the air move. This is why we need a fan. The fan is able to make the rad think the car is moving, through the simple device of air movement. The fan is located immediately behind the rad and is covered with a shroud designed to maximize its suction abilities. Its job is to kick in at just the right moment and pull air through the rad, to help dump the heat that's in the coolant that's in the rad. Such a kick-in moment would be after about 4 minutes in heavy traffic in the middle of summer.

Honda fans are extremely reliable and live very long lives even in areas where snow and rust are prevalent. They are not normally the cause of trouble, but they do need to be turned on before they can work. It's the things that turn them on that go bad, and those things are all...electronic...

In the Old Days (sorry, young feller), cooling systems got along just fine with only the mechanical stuff discussed earlier. You might have had a dashboard gauge or idiot light (and a sender that fed the gauge or light) that told you how hot things were getting, but that was it. Even the radiator fan back then was driven by a "fan belt" off the engine itself, ran all the time, and gave zero trouble unless the fan belt snapped or a blade broke off. The thermostat alone prevented overcooling of the engine, since there was no way of turning the fan off.

Problem is, front-wheel-drive, US government fuel economy regulations (CAFE), and emissions laws all combined to upset the apple cart. Suddenly that belt-driven engine-mounted fan was a power-sapping, fuel-guzzling, unburnt-hydrocarbon generating monster and had to be exorcised from the road. And a radiator doesn't work so well when pointed sideways in a front-wheel drive car, as any owner of a 1959 Austin Mini can tell you.

The final solution (after a number of other ones) was pretty simple: disconnect the rad fan completely from the engine and run it with an electric motor instead. That way, you could put the fan where it should be, behind a front-mounted rad, and only turn it on precisely when needed. This is where some of the electronic controls come in.

	Here's a 1970 Ford 302, unencumbered by emissions controls or Corporate Average Fuel Economy regulations. The fan is firmly bolted to the water pump nose and turns all the time, driven by a belt off the crankshaft. The only concession to efficiency is that the fan's blades are flexible, and sort of bend straight at speed in order to present less of an impediment to engine's efforts at rotation.
	And here's a typical Front-Wheel-Drive setup (a 1991 Integra, naturally). The fan has been completely divorced from the engine (which has got turned sideways) and communicates remotely, through electrical signals only.

Electronic controls back to top

The electronic controls have three basic functions:

Turn the radiator fan on and off
Tell the ECU how hot the engine's running, so it can adjust the fuel/air mixture and the ignition timing
Operate the dashboard-mounted gauge

The controls involve switches, sensors, and relays, along with the wiring and connectors. They're pretty simple in-and-of themselves, but the complication lies in your ability to make sense of electrical wiring diagrams that can look like not much more than inscrutably geometric spaghetti.

Troubleshooting this stuff requires some basic equipment, and lots of well-structured patience.

Some very good links

http://www.babcox.com/editorial/us/us50230.htm
http://www.asashop.org/autoinc/june97/cooling.htm
http://www.caranddriver.com/article.asp?section_id=27&article_id=2334&page_number=1
http://www.caranddriver.com/article.asp?section_id=27&article_id=2264&page_number=1
http://www.valvoline.com/downloads/DTurcotte_Mag_53_g.pdf