What's the advantage of running a pressurized cooling system

Billions of dollars......

 

A radiator coolant expansion system is a closed system. Once the system is full, it works whether the system is pressurized or not. It must remain air tight, though. As long as the radiator is filled to the top, the tube end in the expansion tank is covered with coolant when the system is cold, and there are no air leaks in the system, it works...pressurized or not. There must, of course be an exit for air to exit/enter, as the coolant enters/leaves the tank. To answer the question...a pressurized system raises the temperature at which the coolend starts to boil off. Modern cooling systems run at around 210-212 or so. This allows the engine to more completely burn all the fuel. I will be running a non pressurized cooling system, and an expansion tank with 50/50 mix, on the engine in my Avitar. My reasoning is that if the coolant boils with a 50/50 mix, then the engine will be running too hot, and somethings wrong...

 

Fix the leak and install a new recommended poundage pressure cap for the year and engine that you have. They are cheap and they do go bad. If it came with a pressure cap, there is a reason for it. If it didn't come with a pressure cap it isn't needed. Trying to outsmart the engineers gets people into trouble. IMHO. They were pretty smart cats.

 

WOW. Alot of responses. I will get it fixed and continue to run the 4# cap. I was not certain on how the whole thing worked and was not sure of why most cars run a pressurized system. Now I know more. Thanks, Todd

 

A few years back I wondered why guys at the track would start to panic when the gauge started past 180. After all, stock modern engines run at much higher temps for hundreds of thousands of miles without seizure. Then I realized that the tracks aren't allowing racers to run coolant because of clean-up h***les and the slippery factor not to mention flammability.

 

Agreed.

However, does a zero pressure radiator cap allow for that? I've never used one. My thinking is that if the cooling system does not allow for pressure to build up, it also would not allow for any kind of siphoning action. Of course, if the cap has some kind of backflow valve that seals the system when cool down is occurring, then the siphoning action would result. Does the cap have such a set-up?

 

This guy built the one of the first waterpump dyno and does a lot of R&D for racing
http://www.stewartcomponents.com/tech_tips/Tech_Tips_2.htm

 

You couldn't be farther off the mark. I didn't see one person address optimum operating temp. In the last 60 years we have learned a lot about combustion and how to control flame propogation to maximize efficiency (read that as max btu release from fuel), to say nothing of emmisions. We are getting more power from every pound of fuel than ever before. We are doing this with better fuel control, better spark control and better temp control. One of the things we have learned is that combustion efficiency depends on adequate temperature and anything below 180* oil temp, and 200-220* water temp is often hurting combustion. This is why a modern engine runs 14+ lbs of pressure and has a 190* thermostat to maintain normal water temps around 210*.
Why would that matter today in your 40-60 year old powerplant? The fuel has changed. You may be clinging to that old reliable dizzy, 6 volt coil and non-resistor wires, your strombergs and open cooling system, but you can't get the same fuel all those parts were designed around. You are lucky to avoid 10% ethynol blends, especially in summer. You need to adjust your entire set of operating parameters to suit today's fuel if you want that old mill to work at peak efficiency. That means jetting and tuning to the gas, heating up the spark, considering compression ratios AND getting it all to the right temp.

Don't believe me, go read what Smokey Yunik, Carol Shelby, and few lesser known folks with years in the performance game have to say about engine temps. You have to get it hot to burn it all, you have to burn it all if you want all the energy stored in those poorly atomized droplets your feeding that otto cycle compressor.

 

For every pound pressure the cap is, it boosts the boiling point by 3 degrees. So a 15 lb cap will boost the boiling point by 45 degF. Water boils at 212 so with a 15 lb cap you have a boiling point of 257 degF. Most 50/50 mix cooling systems need to have pressure for it to work properly, there are exceptions, downside is boiling point is much lower and prone to boilover.

 

Some years ago there was experimentation with ceramic blocks because it was recognized that lost heat was lost energy.

My fear with low boiling points would be cavitation. I've worked on more high pressure piston water pumps than engines and have seen how those little tiny steam explosions in water can eat through a cylinder wall.

 

Wow, great thread, as I am currenty working out the bugs in a new moter, its runnin hot 212-220-230 as per what I thought, but maybe its not IDK

 

i have a headache after reading this thread!

 

The reason for a pressure system is, water boils at 212 at 0 pressure, adding a pressure cap, say 13 lbs, raises the boiling point of the water to about 240-250 Deg depending on how far up the mountain you are. If you need proof, try to remove the cap on a hot engine, and you gona get burned, cause you got 240 deg water and 0 pressure, and 240 water is doing a good boil at 0 pressure. So you can run higher temps and not loose your coolent, plus you can now run a closed system with a puke tank and everything stays nice and clean, cause you eliminate the oxygen in the water, and oxygen is bad for ANY cooling system. Oxygen is corrosive, and it also has 0 capisity for removing heat molocules. Dead water (water with out air) is excellent for heat transfer. Iceman

 

The short answer is yes.

Long answer:

If you look at a radiator cap from a pressurized system, you'll see that the cap seals to the very top lip of the radiator neck, and then there is also a seal with a spring between it and the underside of the cap. This lower seal fits agains that smaller-diameter opening about an inch or so down into the radiator neck. The seal right under the cap is what seals the radiator from leaking out the neck, and that spring-loaded seal is what determines the pressure rating of the cap. In other words, if there's a light spring there, then it doesn't take much pressure to push open that seal and let coolant flow to the overflow reservoir. If it's a heavier spring then it's a higher pressure cap. Note that there is also a check valve (little loose disk in the center of the lower seal) which closes once the system begins to build pressure, but also lets coolant flow back into the radiator when it cools off.

You can turn one of these into a "zero" pressure cap that will still seal, by just tearing off that little check valve disk. This will allow coolant to flow back and forth to the overflow reservoir without having to build pressure in the radiator first, and it will siphon back once things start to cool off.

 

Ok so this is all very interesting, but here is another question that comes to my mind, If optimum power comes from a hotter engine, then say like mid 60's ford that call for a 160* thrmostat, should we all be replacing them with like 180*'s or higher and running a higher # cap, or do we risk the chance of blowing the rad and heater core with a higher # cap?

 

I just returned from the radiator shop...my core was leaking at the corners...its a US radiator thats about 8 months old..it had about 6 leaks in it and the guy said it was due to not enough solder when they made it..they guy also told me to run a 16lb cap (the same one that it had on it)...

 

so it sounds like it's ok to use a stop leak such as alumiseal ....right? I have a small seapage at the core to one side tank (plastic) on my beater daily driver. Great thread btw....

 

The actual reason for running a pressurized cooling system is to keep the engine from damaging itself.

Water boils at 212*F, 100*C. Do you think the coolant circulating around the exhaust ports in your head sees temps higher than this? YES IT DOES!!!

When zero pressure encounters these "hot spots", it flash boils... Not un-like a pot of water on your stove just before it reaches a rolling boil.

Those small bubbles on the bottom of the pan, that stay there and never rise to the top are actually insulating the water from the pan.

Similarly, inside your engine, the coolant will make those same kind of bubbles around the hottest parts... Those bubbles "insulate" the hot spot from the coolant, preventing the coolant from doing it's job of picking up the heat and carrying it to the radiator where it can be disapated to the atmosphere.

In a worst case scenario, the entire inside of the engine could be so hot, that steam bubbles form on all the surfaces, and the coolant cant pick up any of the heat... It's theoretically possible for an engine to overheat to the point of warping or cracking components while the coolant and/or temperature guage is telling you that everything is fine...

Pressurizing the system keeps the insulating bubbles from forming, keeping the coolant in contact with the hot spots, allowing the coolant to do it's job of keeping the engine from overheating and damaging itself!!!!!!

Look up the web site to Evans Coolant for a more in depth explination.

 

Hello, I am putting 1966 caddy 429 into my 1937 packard business coupe, my existing radiator is designed at no pressure, do I need to go to pressurized system to cool this beast? Appreciate any advice. Rich