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How hot is hot?


49 Packard
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OK, I'm <span style="font-style: italic">not</span> trying to convince myself that my 288 is not overheating, but I'm wondering just what "hot" really means in "relative Packard terms".

Sitting at idle, my temp gauge rises to about 1/16" shy of the "H" dot. A thermometer in the radiator tells me that is 180 degrees. Does that seem accurate?

Secondly, at what temperature should I consider my car as truly <span style="font-style: italic"><span style="font-weight: bold">running too hot</span></span>?

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To give you a proper answer, let's review a little background on the basics of automotive cooling systems.

The hotter AND MORE STABLE the MOTOR runs, the more efficient. Problem with that is, until pressurized cooling systems came in, around 1938, anything approaching 212 F (at sea level - could be as low as 180 at altitude) results in substantial water loss. So cooling systems up till that time had to keep the temps around 160.

By the early 1920's, the engineering critera for designing cooling systems became so well developed, ( with the exception of the really cheap cars), radiator manufacturers and engine designers produced cars that simply did not overheat except under the most incredibly severe conditions, so long as the cooling systems were properly maintained.

By the early 1930's thermostat technology had reached a point that car designers could have REALLY powerful cooling systems, with operating temps. controlled by the thermostat (think of a thermostat as simply a "switch" that closes off water flow to the cooling system until it gets hot enough. However, engineers recognized that the public wasnt smart enough to accept higher temps, so they continued to "spec" thermostats in the 160 range in summer, until well after World War Two.

In "specing out" radiators, Packard was no different than any other major manufacturer - they were not about to put production out that would over-heat. EVER. So long as your car's thermostat can control the operating temp. to at or below 180 degrees, sounds to me your cooling system is working just fine. Under the most EXTREME conditions I can imagine ( pulling a heavy trailer up the notorious " Needles Grade" in a mid-August afternoon) I would accept temps approaching 210 - but your pressuirzed cooling system will handle that.

If your radiator isnt keeping your car within "spec", my first choice, if you can afford it, is simply have it re-cored. Metal being what it is, and water being what it is, there WILL be corrosion that CAN NOT be completely removed by "rodding". Besides, modern radiators (assuming they get you the correct core) are even MORE efficient than what your car came with.

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Running at 180 degrees at an idle would be completely normal if your car has a 180 thermostat. If it doesn't and instead has a 160 for example, that's slightly overheated but if it's a very hot day, and as soon as the car begins to move a bit it comes back down, I wouldn't be concerned about it. As far as what constitutes "running to hot", you can get as many answers as there are correspondents to this website. I'd say a temperature of 200 degrees while running at road speed is "hot".

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Thank you very much to all who responded to my question. I sure appreciate the history from Peter about how we got where we are (or rather, "were").

I won't get to drive again until Saturday. I'll see what I can figure out, but it's good to know that 180 degrees (or a little more) is acceptable.

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You may have a faulty temp sender, or gauge. I remember someone telling me at one point in time that the temp at normal operating temp (around 180 degrees) should sit dead middle of the gauge.

I think this applies to most of the guages on the Packard where the middle reading is 'normal'. But I could be wrong on that.

Sometimes simply cleaning the terminal connection at the the block temp sender may improve the acuracy as it all based on resistance to ground.

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We have to realize we all have a bunch of 50+ year old gauges. One guage may register 1/8"-1/4" differently than another car at the same actual coolant temperature.

One engine settles at 2/3rds of the way to hot on a cruise while another runs at 3/4ths. Yet neither overheat and are efficient in all other areas. That is a comparison of my Northstar and another person's. Same for old Packards.

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