In working on our old cars, we all know the importance of a clean and efficiently working cooling system.  When a car has sat for a long period of time, one of the first things we do is to go through the entire cooling system, rodding out the radiator, checking the water distribution tube, removing the freeze plugs, cleaning out the block, making sure the water pump is working and the thermostat opens at the right degree; many times overlooking the obviousthe radiator cap.  If it didn't appear to be leaking, I usually didn't change it.  Recently while reading through some Packard and Buick service letters, I read that 80% of overheating problems experienced in their shops were caused by faulty radiator caps.  I then checked the caps on all of our cars and noticed a difference in how the caps were made.  Some were short, some were long, while some had pressure systems and some did not, and I wanted to know more about why the systems are different.

        The basic type of cooling systems are liquid and air, pressurized and non-pressure, and open and closed.  The "open," an older kind of system, was a radiator with an overflow pipe which expelled coolant when hot and pulled air into the system when the system cooled down, reducing cooling efficiency.  The "closed" system uses a special radiator cap and overflow reservoir tank, making what used to be the overflow into a connection between the radiator and the bottom of the reservoir, thus eliminating air in the system and providing better cooling.  

        The early cars had non-pressure systems, in which the water circulated via a water pump without pressure, boiling at 212 degrees Fahrenheit.  In the late '30's, many car manufacturers began using pressure systems.  They found they could raise the boiling temperature by increasing pressure in the system.  For each pound of pressure exerted on the system's coolant, the coolant's static boiling point is raised by approximately 3 degrees F, ie"  a 4# cap boils at 220 degrees F (at seal level), 7# at 230 degrees F, 9# at 234 degrees F, and a 13# cap at 243 degrees F.  The higher pressure also transfers heat from the cylinder heads in a more efficient way.

                During this time, Harrison Radiators were used by GM and other car manufacturers, along with AC caps.  There were three cap designs:  The Internal Valve Type named because of the internal location of the pressure relief valve, and was used with a flat bottom filler neck requiring a fibre gasket to seal against both pressure and leakage (Figure 1).  The internal valve controlled the maximum pressure, but was dependent upon a tight seal at the gasket joint.  The original installation was for passenger cars intended to control the loss of coolant due to surge aeration and after-boil expansion.  During WWII, a larger model of this same design was developed for use on military trucks and tanks.

        This pushed the limits of the design, showing its weakness which was gasket damage while filling the radiator.  To remedy this, the filler neck was turned down, creating a flange around the hole (Figure 2).  Even with the flange, there still was leakage caused by a dried-out or damaged gasket.

        This led to the development of the External Valve Type Cap  This used a beaded surface in the flange of the filler neck to seal against both pressure and cap leakage.  In this design, the valve is faced with a soft Neoprene washer which compensates for small irregularities in the sealing surface, eliminating the need for a fibre gasket.  This type of cap provided for a more reliable control of rated pressure and eliminated the possibility of gasket leakage (Figure 3).

        After the war, the cars' hoods became lower, creating a problem with the taller radiator necks.  A maximum neck height was proposed and adopted as standard to permit maximum radiator height in the reduced space.   The cap and neck were thus revised to fit this minimum height (Figure 4).  

                During this time, the tubular core radiator was developed to replace the cellular core type, to with stand the higher pressures.  In order to prevent the installation of a high-pressure cap onto a low-pressure radiator, a series of caps and necks were designed with the widths of their locking tangs corresponding with  the slot widths in the filler necks.  The proper cap for use with a radiator can be selected by measuring the width of the slot in the filler neck as follows:  1/2" slot width = 4# cap; 5/8" slot width = 7# cap; 3/4" slot width = 9# cap; 7/8" slot width - 13# cap (Figure 5).

        Even with the precautions above, it is still possible to put a worn cap of the long, external valve type into a short-designed filler neck.  By doing this, the compressed length of the long cap completely fills the space in the short neck, keeping the valve from opening to relieve pressure by expansion and vaporization, resulting in serious damage to the radiator core and tank.  Newer caps with sleeves enclosing the spring, help to prevent the spring from being compressed enough to fit in a short neck.  It would be something to check when you buy a NOS or a NORS cap.  

        Some heating problems may be eliminated by using the correct cap, and when an oversized radiator core is installed, check with your radiator shop to see if going to a higher-than-OEM-recommended cap would be beneficial.  Keeping the engine temperature low can add years to the life of your engine!

        Having said that, the bottom line is that most of the pleasure of the Driving Old Cars experience, is to have the car running right!  If it's a V-8, when you punch it you want it to GO.  If it's a straight 8, you want it to run smoothly and quietly.  Foreign noises disturb the experience.  Many times, a noise can be external and mimic an internal noise.  After tuning up our  '49 Buick Roadmaster 320, we put the spark plug cover plate on and one of the nuts was inadvertently left a little loose.  When the engine was warm, the cover plate didn't rattle, but when we started the engine cold, it made a rapping sound like a bad rod bearing.  We discovered the loose nut, tightened it down and the sound went away.  

        Another time while working on our '58 Buick 364, there was a bad bearing-type sound that seemed to be coming from the water pump when we started the engine.  The car had been sitting for 5-6 months, so I got out the motor scope to try to pinpoint the sound.  I listened to the water pump, then the generator (which runs on the same belt).  The sound was louder at the generator.  A few drops of oil in the oiler hole of the generator quieted it down, then the sound went away entirely.  I could have replaced the water pump and still had the noise.  Spending time isolating the sound and being aware of telegraphic noise from one part to another can save time and money.

        The most obvious external noises besides brackets, covers, etc., generally come from the fan and belt, generator/alternator, starter, carburetor, fuel pump, lubrication system and vibration damper.

        FAN NOISE usually has a clicking or rattle at operating speed.  A fan blade might be bent and hitting (check for a bright spot on the water pump or close-by surface where the fan would hit).  If it is a ball bearing fan, check for a bad bearing.  This will produce a clicking sound.  A loose fan might produce a rattle.  Some aftermarket 6-blade fans can produce a squealing sound.  When you change fan belt styles, be aware that a corrugated belt might sound differently from a standard belt.  The belt's notches are like gear teeth, trapping air in the spaces between the pulley and the notch.  If the corrugated belt is chamfered on its edges, it will eliminate any noise by letting the air escape.

        GENERATOR:  If the armature does not rotate freely, it might produce a noise, possibly from bad bearings or a bent shaft.  This usually shows up as scores on the core of the armature.  Loose brushes might cause thrown windings on the armature.  Bearing bind usually causes a squeal.  If the generator/alternator belt is too tight, or the brushes are bad, this might also produce a squeal.  If the bearings are bad, that usually shows up as a grating sound.  Sometimes you can get lucky and there can just be dirt or grit on the bearing, and not actual bearing wear.  A knocking sound might result from too much end play

        STARTER:  A noisy starter has similar symptoms as the generator.  Gear reduction starters will be noisy if gear teeth are broken.  If the starter is not in alignment with the flywheel, the gears will clash, producing a rasping sound.  The gears of the starter drive must also have proper backlash.  If the pinion rides too high on the flywheel teeth, a meshing sound will result when starting.

        CARBURETOR:  It is normal for a carburetor to make a hissing sound that increases when it is throttled.  For backfiring, fuel intake and quantity should be checked, as well as timing, ignition system, air leaks and valves.  Always check your air cleaner for clogs and obstructions.  A dirty air cleaner might produce a rich-running engine, creating a rumbling noise from an open exhaust.  A loose air cleaner or bracket can produce a rattling noise.

        FUEL PUMP:  My favorite fuel pump story is from my good friend Ron Carpenter.  He was once working on a '41 Packard that used the fuel pump mounting bolt bushings.  They had been left off of the car, and the fuel pump was vibrating on the mounting bolts that produced a rod-knocking sound.  When Ron installed new bushings (he makes them), the noise disappeared!  Sometimes you get a break.

        There are, of course, more serious noises, such as a broken rocker arm spring, bent rocker arm, rocker arm binding on the shaft, or anything that would keep the pump from running on the camshaft.  on combination fuel/vacuum pumps, check for all pump part clearances.  The pump will be noisy if the rocker arm pin is worn, the fuel pump link is striking the upper diaphragm protector, or the vacuum pump diaphragm spring is rubbing on the fibre bushing.  insufficient fuel pressure is almost always associated with the above problems.

        LUBRICATING SYSTEM:  Noise in this system can be caused by too high of oil pressure or oil starvation.  I remember once we were working on our '46 Packard 282 CID.  We had completely disassembled the engine, put in new rings, did a valve job, pressure-washed out the block.  We thought it was clean.  After we put it back together, we switched from 30-weight, non-detergent  o il to 30-weight detergent oil.  After test-running the engine, then starting and stopping it a few times, it started to squeal.  We shut it off, but not before taking out #5 rod bearing.  The detergent oil had done its job and cleaned out what we had missed.  When we removed the oil pan, sludge was all up into the oil screen.  I'll never do that again!  Unless the engine comes out of the car and is oven-baked, I'm sticking with the oil it was born with.  Other noises might be heard from a failing oil pump, which will usually show low oil pressure.  A restriction of the connecting rod oil passages might create a knock like a bad piston pin or push rod.

        VIBRATION DAMPER:  Once on a '54 Cadillac, we heard a noise coming from the front of the engine.  It sounded like a rod bearing noise.  It turned out to be a cracked damper.  A bad damper can also produce a vibration.  When rebuilding your engine, it's always a good idea to have the damper rebuilt.  (We use the Damper Doctor, in this magazine.)        There are other miscellaneous noises:  Loose manifold heat control valves can produce a rattle or know similar to a bad piston pin.  A stuck-closed heat riser can overheat an engine, causing it to rumble when shut off.

        Being able to find and diagnose these sounds gives confidence and independence to the owner, making Driving Old Cars even more fun!

        See you next month.  Keep 'em driving!