Purge tank set up
 

When I bought this tank and had 2 vent holes. One on the passenger side of the tank and one off of the radiator cap opening. I noticed that some tanks do not have vent on the passenger side of the tank. I connected this to the top of the radiator. I am now trying to expel a air bubble somewhere in the system. I have the holes drilled in the appropriate place on the thermostat. If an air bubble escapes through this hole I don't understand how it gets out of the system. Does the pressure open the seal of the radiator cap and escapes through the vent line. It seems like the way I have it set up that if a bubble gets into the top of the purge tank it just recirculates to the top of the radiator. Should the line going to the top of the radiator be eliminated.Thanks
http://www.clubcobra.com/photopost/d...diator_001.jpg

The air pocket that you speak of is acceptable if it is totally collected into the tank. The air will seek the highest point in the system thus allowing coolant to displace it and contact the surface of the block or head and provide cooling to the contacted surface. The small hose from the radiator to the puke tank allows trapped air in the top of the radiator to be purged while coolant is filling the radiator.
I will go out on a limb and say that the Overflow tank as we know it was originally developed by Ford because the styling of the cars and radiator design incorporated in vehicles that had hoods that hinged at the front. It may have been that the heads in the "NEW" FE 332 in 1958 were higher than the top of the radiator and was necessary to allow the air to be purged. The tanks were not used in pickup truck applications maybe because of the ability to install taller radiators (?).

The air bubble is circlating through the system. My temp will run 185-190 then jump to 220 and go back.

The tank was Fords early attempt to eliminate air which causes foam in the coolant system while allowing for coolant expansion when hot. They have since gone to coolant recovery systems to make the coolant system a continous flow of liquid and and eliminate air. With the surge tank the air would just seperate from the liquuids flow at the coolant systems highest point. Points to remember are the head gasket coolant passages are blocked at the front . Coolant goes rearward in the block and forward in the head. The little hose between the intake manifold and coolant pump is your thermostat bypass . It will circulate coolant within the engine and pump. Once the thermostat opens the tank and radiator get involved. The modern thermostats with the small bleed hole are a great help. It lets a small quantity of fluid and air escape at the thermostat outward to the tank. This helps eminimate trapped air early in the filling proscess. I'm using a closed system cap (the one with a double seal ) intended for use with a coolant recovery system beyond the pressure cap on the surge tank. I have another colection botttle beyond the pessure cap at the surge tank to try allow for coolant expansion and keep the tank full of liquid to elminate any air that may cause foam. My bottle is actually a 1 qt. water bottle and holder intended for a bicycle. When the coolant in the system cools and contracts coolant is pulled back from the collection bottle keeping the rest of the coolant system full and preventing a colapse of the system hoses , tank and radiator due to vacume.

Mike, where did you mount the bottle?
Thanks, John

Are you saying your bottle is attached to the overflow hose below the radiator cap. So this bottle can be below the surge tank. When cooling is the fluid pulled back through the radiator cap seal. What pressure radiator cap are you using. Thanks for your help

Micheal, Are you there? I am really interested in your response.

I have the bicycle water bottle bracket clamped to the X frame in front of the engine. The clear plastic 1 qt. bottle just slides into it with a little effort. I kinda removed the nozzle and have the hose stuffed through the cap to the bottom. I have a piece of reinforced urithane hose that I can kinda see through, running between the bottle and vent tube under the pressure cap. My radiator is a cross flow with tanks on the sides and no fill cap. Coolant goes in top left and returns from bottom right. I have a metal tube on the bottom that crosses back over to the coolant pump inlet. Radiator pressure caps originaly had one rubber seal to seal off the pressure in the system down inside the filler neck. At pressure it would vent to the tube which may or maynot be connected to a hose(usually directed to a place where coolant wouldn't cause a problem.. A small metal disk in the middle of the cap seal would open to let outside atmosphere back into the system when cooling.
Pressure caps are designated for open or closed system. The newer style being the closed system . They have the original seal and a second seal that seals against the top flange on the filler neck. The vent tube on side of the surge tanks filler neck ( or radiator filler neck ) is located between the lower system and the top flange surface. If the seal are doing there job the inside holds pressure up to the rated pressure. Excess pressure will push that seal off its seat letting presure vent into the cavity below the top seal. That is where the metal vent tube is. That hose is connected to another tank or bottle by hose. Exscess fluid is then pushed from the main cooling system into the recovery tank or bottle. When the cooling system cools and shrinks. That metal disk in the main seal opens. Rather than pull a vacume that would crush the radiator and tanks and such ,coolant is sucked back into the main system. Keeping the systen full of fluid no air that would form foam. Oh, I have metal spring inside the hoses so they won't suck flat. Also when examining a pressure cap the lower rubber seal should not be swollen out beyond the large metal reinforcement disk. Oils will do that. I installed a closed system cap similar to the one you have shown. The hose in between the vent tube and coolant recovery bottle pretty much stays full of green fliud. When system is hot fluid level in the bottle is high. When cool fliud level in the recovery bottle is lower.
Have I helped or confused you.?

That extra vent tube on the surge tank is a great idea it gets any air bubbles out of that side of the radiator through the surge tank.