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Old 09-12-2007, 07:50 AM
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Plumbing a coolant surge tank - need help

The top of my cross flow radiator w/cap (20lbs) sits below the level of intake manifold. The fill point is an additional cap (16 lbs) that is mounted directly over the thermostat on the intake manifold. I have been told that the pressure from the water pump can actually push coolant out of the cap at the fill point which seems to be the case. The solution suggested is to install a regular neck for the thermostat and a surge tank higher than the engine. I have identified a location and the hose from the bottom of the surge tank to the inlet side of water pump will be no problem. I have a question about the "bleed" line to the highest point of low pressure side of radiator. Before I have a bung soldered in can I use a cap from a pressure testing kit and plumb the "bleed" line to the top?

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Old 09-12-2007, 08:01 AM
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What kind of car/engine is this? I just can't visualize it.
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Old 09-12-2007, 09:15 AM
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If you install a surge tank and connect the hose from the bottom of the surge tank to the bung at the radiator fill cap, which is the overflow outlet, then install a new style radiator cap on the radiator the overflow bottle will feed into the radiator when the engine cools down. That will top off the radiator.

The additional step is when doing the intial fill to warm the engine up to operating temp with the radiator cap off. When the thermostat opens have someone rev the engine up to around 2000 RPM and fill the radiator to the top. Then install the cap and lower the RPM. That will insure a full fill. Fill the surge tank half full and you are done.
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Old 09-12-2007, 10:46 AM
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Quote:
Originally Posted by MI2600
What kind of car/engine is this? I just can't visualize it.
39 willys w/bbc 396
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Old 09-12-2007, 11:18 AM
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Quote:
Originally Posted by Rick WI
If you install a surge tank and connect the hose from the bottom of the surge tank to the bung at the radiator fill cap, which is the overflow outlet, then install a new style radiator cap on the radiator the overflow bottle will feed into the radiator when the engine cools down. That will top off the radiator.
Thanks for the input - this is a setup that came with the car and hard to explain. I forgot to mention that the radiator being well below the top of the engine does not have an overflow outlet just a cap. That is why I put a 20# cap on it and run a 16# on the fill point cap. The overflow is connected to the fill point. The problem is that water pump pressure at higher rpms is forcing coolant through the cap and into the overflow so I have been toldThe surge tank at the highest location will solve this but I need a way to plumb the bleed line. Pulling the radiator to have a bung soldered in is quite a chore and that is why I asked if I could just use a radiator pressure tester with the line coming out of the cap on the radiator.

Quote:
Originally Posted by Rick WI
The additional step is when doing the intial fill to warm the engine up to operating temp with the radiator cap off. When the thermostat opens have someone rev the engine up to around 2000 RPM and fill the radiator to the top. Then install the cap and lower the RPM. That will insure a full fill. Fill the surge tank half full and you are done.

Fine for a conventional setup but my setup has the radiator well below the level of the engine. My fill cap is on the intake directly above the thermostat. When the thermostat is open and the cap is off the coolant is forced straight up and not into the radiator.
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Old 09-12-2007, 11:58 AM
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All you will need is a puke tank tank, The 20# cap at the thermo is fine. You are experencing expantion, I beleive.
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Old 09-13-2007, 05:01 AM
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Quote:
Originally Posted by wildman1932
All you will need is a puke tank tank, The 20# cap at the thermo is fine. You are experencing expantion, I beleive.
No! The water pump pressure is forcing more coolant out of the cap than my puke tank can hold. I need to eliminate the cap that is on the high pressure side of the system (over the thermostat on the intake manifold).

Here is a link explaining radiator cap location.

http://www.stewartcomponents.com/tec...ech_Tips_2.htm
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Old 09-13-2007, 07:00 AM
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If you have a true sealing 20# cap, ( one that actually seals up to 20#s) it is not going to leak before the 16# cap opens. I thought you said, it leaked under pressure. Maybe I missed some thing. The pressure from the coolant system comes from heat not the water pump. As the heat goes up, the pressure go up. When it cool you can run it with the cap off, and it should stay in the system.The water pump moves water, but not under pressure. It is not a pressure pump. The design of these pumps do not create pressure, they move water.
If all else fails, take off the fill cap at the trermo, and put a fill on the firewall. Like a remote fill.
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Old 09-13-2007, 05:04 PM
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Quote:
Originally Posted by wildman1932
... The pressure from the coolant system comes from heat not the water pump. As the heat goes up, the pressure go up. ....
I am not losing coolant due to heat - less than 200 degrees by 3 different temp units. See the above link to Stewarts. They explain how the pump pushes coolant pass the cap better than I can.

Basically the surge tank I want to install is a remote fill. I just wandered if I can plumb the "bleed line" through the top of a pressure test cap rather than pull the whole system to have a bung soldered into the rad.

Guess I will just try it and see. Will post the results when I get back into town.
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Old 09-13-2007, 05:58 PM
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look at any 63-67 corvette, thats how the factory solved the same problem, plumb yours the same way. while the pressure tester cap thingie would work i think eleminateing the cap and soldering a bung on top is a far better solution.
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Old 09-13-2007, 07:31 PM
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The way a radiator cap works is that it allows water out into the overflow tube when the pressure in the radiator reached its rated pressure (water expands when it gets hot BUT the pressure keeps the water from boiling) it then allows water to bleed out of the system. then after the motor cools down the water contracts back, causing a vacuum and a small valve in the radiator cap allows the water to be sucked of the overflow tank back into the radiator. This is why the overflow is ported to the BOTTOM of the tank.


I have never seen a water pump that would push a 16lb cap up, most of the time you could hold the pressure back with your hand. Remember water is not compressible. So if there is a restriction in the system THAT bad it would be sucking the bottom hose closed. Also its easy to have 8-12 lbs on the system at 160*, so 200* could easily have 16 depending on the system.

Get a tank off of a small GM car that has a PRESSURIZED over flow tank and route a 3/4" heater hose from the top of the intake to it and then back into the input of the water pump. The cap on the tank will hold 16lbs and if you have a problem with the cap on the radiator you could have it brazed up.
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