Packard Forum Index » General

I have read many postings and listened to many people talk about their engine temp staying around 190 degrees in all conditions. To me this seems wrong. The thermostat is there to keep the water from circulating thru the radiator until the engine warms up past the thermostats rated temp. At the 190 degree temp it is full open. The water temp must rise above 212 or there would be no need for a pressure cap. The fact that there is pressure in the system indicates that the temp is above 212 degrees. How are these guys measuring the engine temp? Most factory gauges only show cold to hot. Not the actual temp. I have a mechanical temp gauge on my 250 ci. chevy van that reads higher than 240 degrees under normal freeway driving and higher than that on hot days. The system does not boil over and I do not ever have to add water. This is the second gauge I have had on this engine with the same readings.

Just can't believe that any engine will run no hotter than the rating of the thermostat.

Another interesting statement more people than I can count have said is that the engine will run cooler if you replace your 190 degree thermostat with a 180 degree one. This is just not true.

Is there something about 30's and 40's cooling systems that is different than say the ones in the 50's? Are they all unpressurized? I know my 31 ford was not a pressure system.

Many, especially of the prewar cars, ran NON pressurized systems because they had radiators BIG ENUF to keep the engine temp lower than 212.

In the post war era there was a hard push to cut cost and accelerate obsolescence. So they put it small radiators and pressurized the system.

Cost-cutting was perhaps an important factor, but another was engine efficiency, with the side benefit of better hot water heaters to replace exhaust-gas powered heaters. Engines run with very significantly better efficiency at higher temperatures and the common antifreeze up to the mid 30s was methyl alcohol which begins to boil just above 160 degrees, so the non-pressurized systems of that era used thermostats of that temperature or less. My 34 Eight has a Pines Winterfront and the standard 160 shutter stat, and the car pretty much runs at 160 regardless of conditions.

As ethylene glycol antifreeze began to gain acceptance, it allowed manufacturers to raise temperatures to get better engine efficiency and also enhance the performance of hot water heaters. Some of these systems were still unpressurized. But just raising the thermostat setting with no other changes brought the operating temperature closer to the boiling point, leaving little margin for overheating.

Pressurizing the system allows you to obtain a reasonable elevated margin between operating temperature and the boiling point. The pressurization does not raise the temperature of the coolant, only it's ultimate boiling point while under pressure.

Take off your pressure cap on a cold engine and start it; and with the cap removed and by watching the water flow in the top tank, you can see when the stat opens by the beginning of turbulent flow, and this starts at the thermostat rating, neither higher nor lower because of pressurization or lack thereof.

My 56 Executive runs as hot as 230 degess F. BUT only gets that hot during 95 F ambient and only while setting and idleing for long periods of time or very slow parking lot manuvering.
As soon as the car gains some sustained speed of say 15 to 20 mph the temp drops. Sustained speeds in the range of 25 to 60 mph the engine temp stays at about 185 F. Speeds of 70-85 it will reach closer to the 200 mark.

If ambient is under 80 f then the sustained higher speeds will only produce about 180F at the highest. Maybe 210 at long idle periods.

In cooler weather of say 50 F and under the temp gauge will rarely reach 190 F regardless of operation.

I'm using a 160 F T'stat. SunPro 2-5/8 dia dial face, bourdon tube type gauge mounted in place of the clock.

IIRC every 1 pound of cap pressure allows for 3 degrees increase in boiling point. Maybe Owen can expound upon that some better.

So a 7 pound cap will allow engine temp as high as 233 F.

Hotter engine = better efficiencey. That's true. But i really doubt that efficiency was the mfg'ers goal at all.
Would the prewar engines hold up at a sustained 190 - 200 degree operating temperature assuming a pressurized cooling system was adapted at the time???? I doubt it. Not many prewar or even pre 1955 engines would run more than 50k miles without piston ring replacement.
SO the efficiency of the post war hotter engine was more or less a positive unintentional side effect of the cheaper radiator combined with technology that stemmed out of WWII.

A prerequisite tO analyze the automobile and/or auto industry of the 20th century is a full understanding of the WWII war effort. Otherwise without WWII technological developemnts one is very apt to "place the cart before the horse".

I mite even add that not even the greatest historians of general US history can even begin to objectively analyze 20th century America without a full analysis of the war years. It is the War years that contrast both eras.

Engines DO normally run hotter than the engine coolant thermostat rating.

IMHO, the coolant thermostat is more of a floor than a ceiling. That is, this thermostat is intended to get the engine up to the designed operating temperature as quickly as possible. Cold engines waste fuel.

The thermostat opens fully at its specified threshold, but it cannot regulate how hot the coolant gets. A lower rated thermostat, in good working order, will NOT lower the ultimate operating temperature. How hot the coolant gets is a function of how much heat the engine generates vs. cooling system capacity to remove it.

A sticking thermostat, however, can cause overheating.

The thermostat opens fully at its specified threshold, but it cannot regulate how hot the coolant gets. A lower rated thermostat, in good working order, will NOT lower the ultimate operating temperature.

I guess I disagree, with reservations. A lower temperature thermostat can lower the operating temperature as long as the radiator/cooling system has the capacity to remove that amount of heat. The issue to consider is that at colder coolant temperatures the efficiency of the radiator is itself reduced, i.e. the higher the differential temperature between the coolant in the radiator and the surrounding air temperature, the more efficient the radiator becomes.

Great information. You all have confirmed much of my thoughts on the subject and brought to light some things I hadn't considered.

With one exception all the cars I've owned had pressurizes cooling systems. The model A was the exception. Always had boil over problems with it on 90 plus days.