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EFV-8 Club Forum / General Ford Discussion / Radiator cap

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Posted By Discussion Topic: Radiator cap     JayChicago 09-06-2020 @ 6:27 PM reply profile send p.m. Member Posts: 480 Joined: Jan 2016 I don't understand why there is so much thought being put into a higher boiling point. If my car gets above 212 degrees I have a problem, and I will stop driving, weather it boils or not. The only reason for using a pressurized cap that I have heard that made sense to me is one put forward by TomO: A cooling system under pressure may prevent the coolant from developing steam bubbles (boiling) at certain hot spots throughout the water jacket. Maintaining the liquid state provides better heat transfer at those hot spots. sarahcecelia 09-06-2020 @ 9:03 AM reply profile send p.m. Senior Posts: 1183 Joined: Mar 2013 If my memory serves me right, every pound of pressure raises the boilimg point 3 degrees. That being said- A 4 pound cap would raise the boiling point to 224 degrees. (212+12=224) Regards, Steve Lee silverchief 09-06-2020 @ 8:38 AM reply profile send p.m. Senior Posts: 520 Joined: Oct 2009 Thanks for the education guys. I live 3,000 feet above sea level. therunwaybehind 09-06-2020 @ 8:17 AM reply profile send p.m. New Member Posts: 180 Joined: May 2019 The most important effect of a pressurized coolant system is in mountains where other wise the coolant would boil at lower temperatures and run out the overflow. Atmospheric pressure at sea level is 14.7 psi so with a 4 psi cap one would be OK to 10.7 psi since 10.7 + 4 = 14.7 would give a boiling point the same as sea level. Permanent antifreeze is what elevates the boiling point of the coolant when mixed with water from water's 212 to 230 or so as well as lowering the freezing point. I realize that folks enamored with chemistry will find this meaningless. The ethylene glycol does not form a bond with the water to create a new chemical compound. When the mixture finally boils the water will boil off first like in still or oil refinery fractionating tower where the volatile gasoline comes out the top of the tower and other denser fraction like fuel oil and eventually residual oil come off lower at their individual boil offs. Where does my insight come from? Commercial airline coffee pots. The airplane cannot fly if the coffee pots are damaged so at the cabin pressure the percolation yields coffee that is luke warm. They are part of the minimum equipment list (MEL) just like the constant speed drives for the alternators for the electrical bus. 51woodie 09-06-2020 @ 8:01 AM reply profile send p.m. Senior Posts: 510 Joined: Jan 2017 Silverchief. I have a 4# cap on my stock '46 Super Deluxe Coupe, and have never had an issue of high temp or overflow. Lucky I guess, if compared to other posts I have read. As trijford posted, these gauges are not the most accurate. I installed mechanical temp and oil press gauges, prior to getting all my dash gauges working, and 180 deg. on the mechanical gauge is about midpoint on my dash gauge. You can check the temp of the engine at the temp sensor in the head and rad inlets/outlets with a thermal heat gun (cheap to buy), and compare those readings to your dash gauge. The only time my engine gets above 180, is to 185 in stop and go traffic, or to about 190 deg. a few minutes after I shut the engine down. One thing that can cause overflow, is the coolant level being too high in the rad. My coolant level cold is only about an inch over the tubes. cliftford 09-05-2020 @ 8:42 PM reply profile send p.m. Senior Posts: 845 Joined: Jan 2014 water boils at 212 degrees, at atmospheric pressure. Using a 4# pressure cap raises the boiling point to about 240 degrees, if I recall correctly. Its basically the same principle a pressure cooker works on. trjford8 09-05-2020 @ 5:07 PM reply profile send p.m. Senior Posts: 4214 Joined: Oct 2009 The 4lbs means that when the pressure in the radiator reaches over the 4 lb mark the cap will allow the radiator fluid to escape out the overflow. Sounds to me like your car is just fine. The gauges are not exactly accurate. I have found that at the 3/4 mark on the gauge the actual temp is 180. Sounds like you may have been in the 190 category. Today's new cars are running almost 220. silverchief 09-05-2020 @ 12:50 PM reply profile send p.m. Senior Posts: 520 Joined: Oct 2009 Besides keeping the. coolant from splashing out .- exactly what does a radiator cap do? What does the 4 lbs refer to? I ask because I had my garage replace the coolant and do a reverse flush on my 46. Outside temp was 80. When I picked it up they advised my oldd radiator cap was not performing as it should, and they put on a new one. En route home I ran into a construction detour that took me the long way, through a lot lot stop lights and stop and go traffic. My temp gauge was moving past 3/4 toward Hot and I felt sure my car was going to quit on me. However, it never reached the Hot mark, and I got home without incident. Can I assume the new cap made the difference in keeping the coolant in a satisfactory range?

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