Packard Forum Index » General

Over Heating
It has been discussed in length on the forum but I felt it would be best if we made a check list for diagnosing overheating issues and the order in which you do them will save you time and further frustration.


External Items are the easiest to access so do them first:
? Fan belt fit (width), integrity and or tension -( Check for glazing and or fraying if so replace)
? Carburetor mixture incorrect / running too lean- ( a gas analyzer can be used to measure exhaust gases) The usual culprit is a bad intake gasket
? Ignition timing - is the timing retarded? Or is the vacuum or mechanical advance failing to advance under acceleration ( In some cases when setting timing be sure to disconnect your vacuum advance to achieve proper timing. Use a timing light )
? Rotting or weakened radiator hose, the water pumps suction can cause them to collapse when engine is under load. - (replace if spongy or collapsed). Some models used a inner hose spring stiffener.
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? Restricted, undersized, or plugged exhaust - ( Check around bends especially around the over the axle portion)
? To thick of paint built up on radiator fins Strip and Repaint with a radiator specific paint a company like Eastwood carries.
? Portions of the radiator clogged creating hot and cold spots - (can easily be checked with an infrared temperature gun. They are fairly in expensive from a hardware type store) The temperature of the radiator should be consistent across the radiator but decreasing as you move down. Cool spots usually indicate a clog. If cool spots are found it is best to remove the radiator and have it boiled, back flushed, or rodded then flow tested. This can be done at a local radiator shop.
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? Improper radiator cap (psi) or wrong height causing pressure not to build -(See factory service manual for specific vehicle specification)
? Torn or ripped gasket on the radiator cap

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? Vacuum leaks causing engine to run lean - (that can be checked with a vacuum gauge) Engine in good running condition will produce 18-22 inches of vacuum.
? Improperly routed exhaust to close to block or oil pan
Internal items to look at: (Secondary once all of the above are ruled out)
? Leaky head gasket that allows exhaust gases into the water passages not allowing the coolant to cool - (A test kit can be purchased at a local Napa test for exhaust gases in the cooling system)

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? Thermostat weak or failing to open and work properly - (Check thermostat on stove in a pot of water with an accurate thermometer) For best results use a pellet type for 1951 on Up

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? Incorrect degree thermostat than stock - (refer to factory service manual)
? Water pump impeller is loose on the shaft or the impeller clearance to the body to great. -(Remove and inspect)
? Impeller blades heavily corroded thus reducing its ability to circulate water. -(Remove and inspect)
? Improperly installed distribution tube( 1935-up) or clogged or rotted water jacket side plate on 20-28 Six and 24 -39 Std 8 and Super 8 -(Remove and inspect)

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The side plate water distribution type will in most cases suffer from the inner baffle completely rotting away. So when you remove the side plate there is nothing remaining and can sometimes be overlooked because you are unaware that a baffle is suppose to be in place.

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? Scale build up within the engine block or cylinder head creating hot spots -( Remove freeze out plugs and or distribution tube and clean and flush engine block)

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James From
Kanter Auto Products.

Excellent lesson!
Thank you,
Mike