I would be curious to see if the car overheats on just straight water. I knew a gal at work that filled her car up with straight anti-freeze and never could figure out why it overheated. Remember it's anti-freeze, not anti-heat. Anything more than 50/50 mix is too much unless you are in the Arctic circle. IMHO

Obviously the main reason for anti-freeze besides changing the freezing point of the coolant is to prevent prevent rust from forming.

Some of those numbers may actually right now be in the process of being superceeded. Probably the best thing would be if someone would go to the local store and see what numbers will remain active as is, and which are changing. Nevertheless, countermen should be able to use these numbers to cross-reference any replacement numbers.

Let's remember that these cooling systems were designed and tested by competent engineers to cope with expected conditions that might be encountered whereever they expected to sell cars. Since Packard historically exported cars to warm locales like Saudi Arabia, India, and Central and South America, we can assume they were designed to cope with these conditions.

Typically a cooling system is designed with a certain amount of overcapacity in anticipation of the fact that deterioration sets it almost immediately from things like build up of insulating corrosion products in the radiator tubes and hard water and other salt deposits within the engine block. The engineering philosophy was probably to design so that, with an average of deterioration, the cooling system would still be adequate for the expected service life of the car, perhaps something like 15 years.

Obviously there are a large range of experiences that can be encountered, depending on many factors, especially the frequency of change of antifreeze (remembering that the antifreeze properties of ethylene glyol doesn't significantly change over time, but the anticorrosive additives have a finite life), the hardness and mineral content of the water used, and just the general care given the car over the years.

Dave those may make a good FAQ topic as the question does come up frequently. Or if someone wants to enter all those numbers in to the Parts X-Ref, then that would be even better!

HOWEVER. Deteriorating cooling systems say 20 years and older can not always handle a pressure cap much over 6 or 7 pounds.

Need to check the cap rating and whether or not the cap meets the rating and has a good gasket.

Overheating temp:

PRESSURIZED cooling systems use a pressure cap. The cap is measured in Pounds. IIRC each pound of cap rating is about 4 degrees.

EXAMPLE: The 55 packard cap is rated at 10 pounds. That means 40 degrees OVER boiling = 252 degrees. AFTER THAT the water begins to boil and will puke out of the overflow tube.

So overheating would be considered anyhting over 250 degrees.

There is some wiggle room on this tho. As Owen states it depends on whether the problem (radiator boiling) is chronic or the result of extreme conditions or unexpected under very cool ambient conditions.

For NONpressurized systems then anything over the 212 degree mark presents an overheating problem.


MOST IMPORTANT is to NOT trust a factory heat temp gauge. They are at best inferior quality across all manufacturers. When in doubt use a bourdon tube type gauge to test with.

EDIT: Under some high heat conditions a small amount of puking at the overflow tube may occur during very hot conditions. Small amounts off and on and here and there during the summer is not a problem. Unless it becomes chronic or excessive it is not a problem.

The Packard Club has been out of the larger red hexes
(1 -15/16) for quite some time. They list them, but when you click on it, it comes up "sorry, can't find item". I recently ordered them from Max Merritt for the same price ($10 for 4)and they work great!
They look just like they have been painted but with real crisp edges, not too shiny, or reflective,either.

Ethylene glycol is not as efficient at heat transfer as straight water.

According to my '51 owners manual, the temp gauge should be in the middle. It it goes to the H and stays there, it indicates a problem. If that is the case, I suggest you take the car to your nearest Packard dealer. LOL

It also states that unpressurized the water would boil at 212 degrees F, but under pressure it would boil at 227 degrees F. Not sure if that helps or not.

Have you checked your antifreeze to water ratio? I put too much antifreeze in a modern engine and had an overheating problem.

The Packard Club is still selling the red hexagons. Go to the Packard Club website www.packardclub.org and click on Online Store. Then click on Decals. There are two sizes of hexagons. Measure yours before you order. I understand they are available elsewhere but I will let whoever knows where else address that.
Ken