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Timely Topics Archive

A Monthly Article for Vigor Enthusiasts (8/02)

 

The Vigor's Cooling System

This month we'll return to our Engine Systems series, to take a look at the Vigor's Cooling system. As we saw in The Vigor's Engine Systems, in any internal combustion engine, friction and combustion generate enormous amounts of heat—enough to cause metal parts to warp and distort and ultimately destroy the engine. The main purpose of the cooling system is to remove excess heat from the engine.

Cooling System Overview

But a cooling system has some other important functions, too. Let's look at all of them.

Remove engine heat—This is the main function. The burning air-fuel mixture produces a tremendous amount of heat—combustion temperatures can reach 4,500F (almost 2,500C). This is enough heat to melt engine parts. Some of this heat is used to produce expansion and pressure to move the pistons, and some of it flows out the exhaust. The rest of it moves into the metal parts of the engine, mostly in the head area. If left uncontrolled, this heat would destroy the engine in a very short time.

Maintain engine temperatureEngine Operating Temperature is the temperature the coolant reaches under normal running conditions. In a Vigor, it should be (roughly) somewhere between 180F and 225F.

Note: For the rest of this article, temperatures will be given in Fahrenheit. If you'd like to convert these values to Centegrade, Click here. A converter will open in a new window.

When a Vigor engine reaches this temperature range, its parts expand to their correct clearances. This assures proper combustion and compression, emission output levels, and performance. A warm engine is a happy engine.

Reach operating temperature quickly—An engine must warm up rapidly to prevent poor combustion, part wear, oil contamination, reduced fuel economy, and other problems. A cold engine is a suffering engine. The Vigor's aluminum pistons won't be heat-expanded (size increases with temperature). This means there is too much clearance between the pistons and the cylinder walls, so the pistons will tend to slap against the cylinders instead of moving up and down smoothly. The oil in a cold engine will be thick, which will reduce lubrication and increase wear. Also, the fuel mixture won't vaporize and burn as efficiently in a cold engine.

Provide heat to the heater—The hot coolant is circulated to the heater in order to warm the passenger compartment.

The main parts of the cooling system (and their functions) are...

Water Pump   Forces the coolant through the engine and the rest of the cooling system.
Thermostat Controls coolant flow into the radiator, controlling the engine's temperature
Radiator Transfers heat from the coolant to the outside air passing through the radiator
Radiator Hoses Connects the engine to the radiator
Fan Draws air through the radiator
Thermoswitch Controls fan operation

These are just the main components. There are also heater hoses, the heater itself, and other things associated with the cooling system, but they're beyond the scope of this article. Gotta draw a line somewhere. There are also fuses and wiring circuits, and we will discuss them, since they pertain to the main components. We'll discuss them as they come up.

The Water Pump

Actually, it's a coolant pump, because modern engines no longer use water for a cooling medium. Instead, they use coolant, which has a much lower freeze temperature than water. It won't freeze when the temperature outside goes down in the winter. (That's why coolant is sometimes called anti-freeze.) It also has additives that prevent rust and corrosion and that lubricate the water pump.

  Water Pump

 

Water Pump

 

The water pump is similar to a fan, except it moves liquid (coolant) instead of air. Since the cooling system is a closed system, the pump builds up pressure inside the system and propels the coolant theough the coolant passages. The pump is driven by the timing belt.

With a water pump, there's not much to do in terms of maintenance or repair except to keep your coolant in good shape by replacing it periodically. There are no adjustments to make. If the pump breaks, replace it. The most sensible thing to do is replace it before it breaks—and the best time to do this is when you replace the timing belt. The water pump is located on the front of the engine behind the T-belt (see illustration at right).

When a water pump goes bad, it may leak (worn seal), it may fail to circulate coolant (broken shaft or damaged impeller blades), or it may make a grinding noise (bad pump bearing). Rust in the cooling system or lack of coolant are the most common causes of premature pump failure.

To replace it, you'll have to remove the timing belt first—that's why it makes sense to do it while the timing belt is being changed. To remove the belt, see last month's article, Changing Your Vigor's Timing Belt. NOTE: If you're going to replace the pump but re-use the timing belt, mark the belt's direction of travel with an arrow (using chalk or a grease pencil). Make sure you put it back the same way.

When the timing belt is off, remove the five bolts that hold the water pump to the front of the engine (use a 10mm socket). Then, remove the pump and O-ring.

Water Pump A new O-ring comes with the new water pump.

Coat the threads of the bolts with liquid gasket. Acura recommends Honda P/N 08718-0001. Permatex Gray is a readily available substitute.

 

Coat bolt threads with liquid gasket

Coat the Bolt Threads with Liquid Gasket

Replace the Water Pump

Fasten the new pump and O-ring to the front of the engine and torque the five bolts to 9 ft-lbs. When the pump is in place, install the timing belt and button up the engine following the procedures described in Changing Your Vigor's Timing Belt.

The Thermostat

Thermostat

 

Thermostat and Thermostat Housing

 

The thermostat responds to changes in coolant temperature by opening and closing valves—a Vigor thermostat has two, a primary and a secondary. The heart of the thermostat is a wax-filled pellet attached to a small piston contained in a narrow cylinder. A spring holds the piston (and valves) in a normally closed position. As the coolant takes on heat, the pellet expands and pushes the valves open. This allows coolant to flow into the radiator. As the coolant cools, spring tension overcomes the pellet expansion, and the valves close.

How do you know if it's working? The easiest way to tell is to watch the temperature gauge on the dash. If the needle stays in the "normal" range  and doesn't go near the red mark, you can assume the thermostat is working fine. But occassionally thermostats do fail, and there are a few ways they can fail.

The most obvious case is when the thermostat fails to open (stuck closed). In this case, the temp gauge will indicate overheating, but the coolant in the radiator will remain cold. Also, the upper radiator hose will have no pressure in it, and you'll be able to squeeze it easily. Feel the radiator with your hand. Be careful, though—it may be hot, indicating a different problem. If this is what you find, though (hot engine and cold radiator), you've got a thermostat that's stuck closed. You can simply remove the thermostat, put the cover back on, and continue to drive the car. Obviously, you'll want to put a new one in the first chance you get, but this'll get you home.

A thermostat can also fail to close (stuck open). In this case, the engine and heater will take an abnormally long time to warm up. Or, the engine may never reach normal operating temperature. It may run poorly in cold weather and the engine's efficiency will be reduced (power, gas mileage...).

Trickier problems to troubleshoot can occur if the thermostat "almost" works, ie., it opens, but not all the way. Or, it closes, but not entirely. Keep an eye on the temp gauge. Use logic and your understanding of the cooling system operation and you should be able to determine if you have a reason to suspect the thermostat.

The thermostat is located inside the Thermostat Housing, and you'll have to remove the Thermostat Cover to get to it.

Stat Housing  
 

Remove Thermostat Cover

 

First, using a 10mm socket or wrench, remove the bolt that holds the engine wire harness cover to the thermostat cover.   See the lower arrow in the photo at left.

Next, remove the two 10mm bolts that hold the cover on. The upper bolt is shown by the upper arrow at left. The lower bolt is obscured in the photo.

Wiggle the thermostat cover away—you may find it easier if you remove the radiator hose from the cover, but that isn't necessary.

Then, pull the thermostat and O-ring out of the housing.

At this point, you have two options. You can put in a new O-ring and a new thermostat, replace the cover (torque the bolts to 9 ft-lbs), and you're done! Or, you can test the old thermostat to verify that it is causing the problem. Since a new one costs under $20, most people won't bother to test it—too much trouble, and putting in a new one will certainly eliminate any doubt. But if you're the curious type...

Put a saucepan of water on the stove and suspend the thermostat in the water. Don't let it touch the bottom of the pan. A stick placed across the top of the pan—with a string tied to the stick at one end and the thermostat at the other—will work nicely. Let it hang in the water. Then, turn on the stove burner, get a meat thermometer, and watch the action. The primary valve should begin to open around 180F. The secondary valve should start to open at 185F. Both should be fully open at 203F. At that point, the primary valve should open 10mm and the secondary 8.5mm.

As you can see, it's probably easier to slap in a new one. But if you enjoy working on cars, it's an interesting thing to see at least once in your life.

 

Continued

 

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