“Parade-Proof” Your Car

August 1, 2009 | By John Ball

Don’t Miss Local Events Because Your Vehicle Might Overheat. Take These Steps…and Roll Into the Spotlight.

Editor’s note: Many people have extreme mixed emotions when they’re invited to drive their vintage car or truck in a local parade. After all, they’re justifiably proud of their ride and welcome the chance to let their neighbors see the vehicle in motion. But just as they are about to agree to participate, they’re hit by thoughts of their pride and joy stalling in the middle of the parade route and sitting there out of commission while the local high school marching band struts past on both sides like a stream parting around a rock. John Ball, a mechanical engineer and former GM employee and USAF pilot, has used the following tips to successfully parade in a 1961 Chrysler, 1959 Edsel and a 1926 Model T

I WAS SURPRISED recently when I learned that many members of our car club were not entering a local parade. They weren’t confident that their cars and trucks could withstand the effort of a long, slow trip.

The parade-induced problem most drivers worry about is overheating.

After all, cooling problems often grow slowly over a period of years and drivers learn to live with minor degradation.

But then the extra thermal stress placed on the engine due to parade driving or a long traffic jam can trigger a nasty surprise.

Without a doubt, every parade driver’s nightmare is the embarrassment of his engine quitting in the middle of a parade. The most common cause for this is vapor lock. Elevated temperatures, even if not reaching actual overheating, promote the vaporization of fuel to the carburetor.

And if the overheating reaches the boiling point, temperatures skyrocket and components such as head gaskets, pistons, etc. can be damaged. The steam pressure can build enough to rupture hoses.

Fouled plugs and other electrical problems are less common problems, but they can force a parade participant to drop out of the festivities as well.

But there’s no reason to let these potential problems keep you—and your ride—from being a center of attention during your next community parade. Time spent in advance, with testing and maintenance, will assure you your proper place when it comes time to roll down Main Street and wave to the appreciative crowds.

Some Testing…

Well before you are scheduled to enter a parade, check your car for any problems that might arise during the event.

On a sunny day, preferably with no wind, let your engine idle for as long as the parade is expected to last or until the maximum engine temperature is stable. Thirty to forty-five minutes should uncover any difficulty.

Monitor the coolant temperature closely as it rises. Rather than trust your dash temperature gauge, use a remote sensing thermometer that utilizes infrared radiation to measure temperatures without requiring contact with the part being checked. This is a valuable tool to find the hot spots on your engine and to calibrate the car’s gauge. As temperature sensors and instrument components age, they often lose accuracy, and you may find yourself worrying about a bogus indication.

Once the coolant temperature reaches the point at which the thermostat opens, the thermostat housing is a good place to check the temperature of the engine. The water temperature leaving this point will be close to the hottest in the system.

What are normal temperatures? Most cars that are modern enough to have a pressurized cooling system operate nicely in the 195° to 220° F range. The boiling temperature of the coolant fluid varies with two factors—the antifreeze to-water mixture ratio and the atmospheric pressure. The boiling point increases as the ratio of antifreeze fluid to water increases. Although 100% water boils at 212° F, unpressurized at sea level, a 50-50 mixture in those conditions boils at 225° F. In a system with a 15 psi pressure cap, it will rise to about 265° F.

An increase in elevation also affects the boiling point. The higher above sea level the car is, the lower the boiling point. Coolant is more apt to boil in Denver than in Los Angeles.

Compare the actual coolant temperature with the specific needle position on your dash temperature gauge.

During a parade, you will be relying on that gauge to signal a problem. We like to see needles in the center of a gauge range, but possibly a reading of 3/4 deflection is the norm for your car. Unexpected readings may be due to a faulty sensor in the block or a problem with the gauge. Check at 1⁄4, 1⁄2, 3⁄4, and full deflection or wherever the temperature stabilizes at its maximum.

If your only temperature information comes from an indicator light, it would be a good data point to know at what temperature it illuminates.

Other checks worth making after prolonged idling are for spark plug fouling and battery charge. Most properly tuned engines will allow long periods at idle without a large buildup of carbon or oil. You also need to know if your battery discharges at an excessive rate.

One last check to make is for dragging brakes after driving your car a distance with several stops. The remote sensing thermometer can come in handy here also by indicating a high temperature of a wheel without worrying about a burned hand. Dragging brakes will cause the engine to work harder with accompanying heat as well as damage to the brake parts.

If your inspection has uncovered a problem, it is likely that bringing the system back to serviceable condition will require only repairing stock parts. Most cars did not overheat when they were new, so what changed?

…Followed by Some Repairs

The overheating problems that we are addressing here basically are slow-speed problems, and the primary causes for those difficulties are airflow problems. Engines that may tend to overheat at cruising speeds are more apt to have coolant flow problems.

Let’s begin with simple issues first. Clean all debris from the fins of the radiator and straighten bent fins. These rarely are major problems, but if these small effects are added to an otherwise marginal system, it may cause trouble.

Another fin-related problem is too much paint on the fins. Some owners will spray a coat of paint on the radiator whenever they detail the engine compartment. Paint is not a good thermal conductor and a build-up of paint reduces the size of the air passages between the fins. This combination reduces the heat transfer from the coolant fluid to the air passing by the fins. If you need to paint a radiator, use the special radiator paint that contains reduced solids.

At slow speeds, the fan is the main source of airflow through the radiator. This is in contrast to airflow produced by vehicle motion at cruising speed. Check that belt tension is proper to avoid slippage. If your car is modern enough to employ a fan clutch, ensure that it is operating properly.

Many cars originally had a shroud around the periphery of the fan that increased the effectiveness of the blades. In past years, this shroud may have fallen off or not been replaced after maintenance. It would be worthwhile to ascertain if your vehicle originally had one. Photos in factory manuals or brochures and technical advice from car clubs are good sources of this information.

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A heat riser locked by corrosion in the “hot air on” position will add unwanted engine heat.

Some cars without shrouds had baffles around the radiator to preclude warm air that had passed through the radiator from flowing back around or over the top of the radiator and passing through again. This recirculation of hot air can soon reduce the effectiveness of the radiator. At normal cruising speeds this is not a problem. At walking speed or when stopped, it can lead to trouble. If your car is missing its original baffle, you may need to construct one if an original one cannot be found.

In our attempt to reduce as much heating of the engine as possible, we need to examine two more sources of heat on older design engines—the heat riser in the exhaust manifold and the heated air system to the air cleaner.

The heat riser valve was designed to direct heated air past the choke heat sensor to improve the choke positioning for cold starts. It also improved the vaporization of the fuel by heating the air-fuel mixture in the intake manifold before it got to the carburetor. Many cars also fed heated air through the air cleaner to assist in rapid warming of a cold engine. If either of these stick in the position to supply heated air, they will be sources of excess heat after the engine is at normal operating temperature or above.

Very few heat risers have been properly lubricated through the years, so they are often found frozen in one position. They are not easily freed up and rebuild kits are extremely rare. If luck is with you, yours will have stuck in the position blocking the hot air. If so, little will be lost by leaving it alone. However, if it has stuck in the “hot air on” position and you are unable to break it loose, consider cutting the mechanism out or find another exhaust manifold. Loss of the mechanism will only cost you a little longer warm-up time after cold starts.

If all this work on the airflow system has not cured your overheating difficulty, move on to the coolant flow area. Ensure that you have the proper amount of fluid in the radiator and have your radiator cap tested for the proper pressure relief and a functional seal. A correct cap is not expensive, so you may prefer simply to replace it.

A frustrating cause of overheating may arise after you have drained and refilled your cooling system—air may be trapped in the block. Some engines have a bleed valve to release this air. If your engine does not have one and you suspect there’s air in the system, disconnect a heater hose to bleed the air.

A major source of problems with overheating involves the thermostat. If yours is defective, missing or installed incorrectly, you can be sure that it will cause a problem. A thermostat can be damaged by overheating so if your car has overheated in the past, it is even more important that it be tested.

A quick check can be done without removing the thermostat from the engine. As the engine warms up, check the temperature of the thermostat housing with your infrared thermometer. (See photo on page 24.) You will find it rising until it reaches the temperature set to begin opening the thermostat. It will stay at that temperature until the thermostat is fully open. It will then continue to increase. That pause in the rise shows that the device is opening, at least partially. A more complete test would be to remove the thermostat from the engine, place it in a pan of water, and heat it until the thermostat opens. Note the temperature at which it starts to open and verify that it opens fully at a higher temperature. It is not unusual for one to not open completely and thus create a restriction in the coolant flow through the radiator. If there is any doubt about the operation of the unit, replace it.

Be sure to follow instructions for installing a new one. Usually, there is a hole in the valve to ensure air is not trapped behind it.

Keep in mind that cooling systems were designed to have a thermostat in the circuit. Operating without one will reduce the effectiveness of most systems and may actually cause overheating and possible damage to others.

Many owners believe that if their hoses look OK and are not leaking, they are fine. In truth, the inner linings can swell, reducing the useful diameter and restricting flow. Hoses softened by heating and without spiral wire support can collapse, but this usually happens at higher speed when a fast flow tends to suck them closed. It rarely happens at idle speed.

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Make certain that parade decorations or signs won’t restrict air flow through the radiator. And also be sure that items like the little hitchiker on the cowl don’t interfere with your vision.

Corrosion in the block and radiator may restrict enough flow to cause overheating even at very low speed.

If it has been awhile since you flushed your cooling system, you may do it to relieve a problem or do it as a preventative measure. Flushing is more effective at cleaning out the block than the radiator. If the radiator is clogged, it will require professional cleaning or replacement. If you suspect a partially blocked radiator, scan the radiator fin area with your remote sensing thermometer after the thermostat has opened. You will see the temperature decrease smoothly as you scan from top to bottom. If you see a sudden drop in temperature, you will have found one or more plugged tubes.

It is ironic that some owners will pay $500 to chrome plate components to make an engine look nice, but resist paying $250 for a new radiator that will protect it.

A hidden source of overheating problems is the water pump. Unless it is leaking badly, no one suspects that it may be the culprit. The impeller can come loose from its shaft and its vanes can corrode. Either one will limit coolant flow.

Three other possible causes of overheating are: improper idle mixture, ignition timing, and a partial obstruction in the exhaust system. If the mixture is too lean, it may overheat; too rich, it may cause fouled plugs. The engine may run hot if the timing is too advanced or retarded.

A lot of effort was expended in the design of engine installations to avoid vapor lock—the vaporizing of fuel in the fuel line prior to it getting to the carburetor. Lines were carefully routed away from the exhaust, and heat shields or insulation were installed to keep the fuel cool and liquid. Checking factory publications or tech support from a car club can verify what your car had when new. If any of these features have been changed or are missing, you should restore them to original condition.

Consider Some Modifications

If the repair steps have not eliminated the tendency to overheat, you will need to turn to equipment modifications.

A more efficient fan usually helps keep engines cool at low speed. If some cars like yours had AC, their fans may be larger or have more blades. Also, there are aftermarket fans with five or six blades that are available for most engines.

The next step up in fan efficiency will come from an auxiliary electric fan. Some push air through the radiator from the front. Others pull air through from the fan side of the radiator. Clearance between the fan and radiator and ease of mounting will determine which would be best for you. Some may be easy enough to mount and remove that you will only use it for parades.

Larger, more efficient radiators are available if the stock one is not adequate. Usually the one that was used when the car was new should be sufficient, but if you modified your car or added AC, you may need the larger one.

If vapor lock is still a problem after the previous repairs, it may be necessary to add an auxiliary electric fuel pump. This will keep enough pressure on the fuel to keep it from vaporizing prematurely.

Let’s hope that one or more of the previous suggestions allow you to complete the idling test without a problem and your vehicle is ready to participate in a parade. With that in mind, here are some tips to help you avoid surprises during the event.

Parade Techniques

The night before the parade verify that all fluids are at the proper level, tire pressures are correct, and the battery is fully charged. It may be prudent to have the phone number of the parade organizer handy to deal with any last-minute issues.

If you will be decorating your car for the parade, ensure that none of the decorations will restrict airflow through the radiator. Also keep in mind that, depending on their placement, some items could shift position during the event and their movement might not be visible from the driver’s seat.

Don’t run the engine more than necessary before the parade begins. Organizers often get anxious just before the parade and will ask you to be ready at a moment’s notice. But don’t be tempted to start and idle your engine before it’s truly essential.

Unless it’s absolutely necessary, don’t run your AC during the parade. It is just one more load on your engine, which means more heat.

If, during the parade, you are getting concerned about how high your gauge reads after prolonged idling, try revving your engine for five to 10 seconds occasionally to move more hot coolant through the radiator. Do not run the engine at a fast idle for long, though, as that produces the worst conditions for cooling.

Only shut off your engine if there will be time for it to cool before starting again. A hot engine, no airflow from the fan, and no coolant flow will drive engine temperatures up rapidly and promote vapor lock. It will be made even worse by the lack of cool fuel flowing through the hot lines.

If, despite all these efforts, the temperature gauge still climbs to an alarming level during the parade, remember that the heater can act as a small auxiliary radiator. Of course, using the heater on a hot summer day will be unpopular with your passengers unless you are driving a convertible. But surely, they’ll understand, won’t they?