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How low would the radiator go after turning the water pump on? How much room should be left for expansion? I am assuming you are telling me not to fill it to the top. Wouldn't the excess when the water heats up just flow into the overflow tank? Did the car run warmer when it was filled to the top? Thanks for responding.

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My radiator does just about the same as yours. I usually fill mine and then turn on the pump and when the level goes down add water until it's about 2 to 3 inches down from the neck and put the cap on


Russ

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Here is a trick I learned when I was racing flatheads. Jack the car in the front as high as the jack can go. Turn on the electric water pump and circulating the water and watch for air bubbles. You should be able to add about a quart extra this way but fill it up to the top of the neck and watch the bubbles dissolve. You are getting the excess air out and doing away with a lot of hot spots in the heads. It will take awhile to do it so don`t get in a hurry.

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If your level drops down when you turn thr pump on, you have air trapped in the system somewhere. No 2 ways about it. Run the pump and fill the rad to the top. If you are running an overflow tank and the correct cap to go with it, the rad should stay filled to the top at all times. The overflow tank is not just to keep the fluid from running out on to the ground, but it is also to keep the rad full all the way to the neck at all times - for better cooling and to eliminate hot spots. When your system is right, there should be no air in it at all. Fliud should go back and forth between the over flow tank and the rad tank as it heats and cools.

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73 dartsport, i have the same system as u. i run my pump with engine off, top off to the neck. i have a closed system. u need a pickup tube in ur puke tank. when ur engine cools it will pull water from tank. i never touch my system. also u can make ur own sight glass on ur tank, 2 90' fittings & a piece of clear hose from the hardware store. stay safe, seeya.

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You need the proper style cap also with a return type
system to go along with the pick up tube

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Here is a trick I learned when I was racing flatheads. Jack the car in the front as high as the jack can go. Turn on the electric water pump and circulating the water and watch for air bubbles. You should be able to add about a quart extra this way but fill it up to the top of the neck and watch the bubbles dissolve. You are getting the excess air out and doing away with a lot of hot spots in the heads. It will take awhile to do it so don`t get in a hurry.

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If your level drops down when you turn thr pump on, you have air trapped in the system somewhere. No 2 ways about it. Run the pump and fill the rad to the top. If you are running an overflow tank and the correct cap to go with it, the rad should stay filled to the top at all times. The overflow tank is not just to keep the fluid from running out on to the ground, but it is also to keep the rad full all the way to the neck at all times - for better cooling and to eliminate hot spots. When your system is right, there should be no air in it at all. Fliud should go back and forth between the over flow tank and the rad tank as it heats and cools.

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Is this true even with an electric water pump and a cross flow radiator? I've heard in the past about needing the right overflow tank with a tube in it, and the proper cap and everything. I don't know much about that stuff, but I was told that a cross-flow radiator will drop when you turn the electric pump on.
I filled my system with a special tool to eliminate any air pockets and left the level 1.5" from the neck and it didn't run hot. But I had no clue if the overflow bottle was working correctly or not.

I can tell you that last summer I filled mine to the top in the purple 69 Dart, don't know if it was coincidence or if a head gasket was leaking but on the 1st pass with it filled up I shot a freeze plug out in 2nd gear and almost hit the wall.
After that I dropped the level and installed a 7 pound cap and raced the rest of the year.

Then, last week, the guy I got the 64 from thought he'd be nice and top off the radiator for me, after a long cruise at only 185 degrees the overflow bottle decided to spray fluid out of the top of the bottle(16 pound cap), right out of the fitting somehow?? I dropped the level and it's been fine.

I'd really like to learn more about the proper way to use an overflow bottle and how to pick the right radiator cap.

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Here is a trick I learned when I was racing flatheads. Jack the car in the front as high as the jack can go. Turn on the electric water pump and circulating the water and watch for air bubbles. You should be able to add about a quart extra this way but fill it up to the top of the neck and watch the bubbles dissolve. You are getting the excess air out and doing away with a lot of hot spots in the heads. It will take awhile to do it so don`t get in a hurry.

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If your level drops down when you turn thr pump on, you have air trapped in the system somewhere. No 2 ways about it. Run the pump and fill the rad to the top. If you are running an overflow tank and the correct cap to go with it, the rad should stay filled to the top at all times. The overflow tank is not just to keep the fluid from running out on to the ground, but it is also to keep the rad full all the way to the neck at all times - for better cooling and to eliminate hot spots. When your system is right, there should be no air in it at all. Fliud should go back and forth between the over flow tank and the rad tank as it heats and cools.

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Is this true even with an electric water pump and a cross flow radiator? I've heard in the past about needing the right overflow tank with a tube in it, and the proper cap and everything. I don't know much about that stuff, but I was told that a cross-flow radiator will drop when you turn the electric pump on.
I filled my system with a special tool to eliminate any air pockets and left the level 1.5" from the neck and it didn't run hot. But I had no clue if the overflow bottle was working correctly or not.

I can tell you that last summer I filled mine to the top in the purple 69 Dart, don't know if it was coincidence or if a head gasket was leaking but on the 1st pass with it filled up I shot a freeze plug out in 2nd gear and almost hit the wall.
After that I dropped the level and installed a 7 pound cap and raced the rest of the year.

Then, last week, the guy I got the 64 from thought he'd be nice and top off the radiator for me, after a long cruise at only 185 degrees the overflow bottle decided to spray fluid out of the top of the bottle(16 pound cap), right out of the fitting somehow?? I dropped the level and it's been fine.

I'd really like to learn more about the proper way to use an overflow bottle and how to pick the right radiator cap.

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Just to clearify things a bit, we are talking about 2 different systems here. An overflow bottle is just that. When the coolant heats up and expands, fluid dumps in to the top of the overflow bottle ( IE. puke tank ). What ever is lost from the rad, stays lost - and that space is replaced by air. If you have a big enough cooling system, no problem. The other system imploys a "coolant recovery" tank. When coolant heats up and expands, it dumps in to the coolant recovery tank, When it cools back down, it is drawn back in to the rad, thus keeping the rad full to the top of the filler neck. Benefit: You utilize all of the rad. You lose very little coolant over time. You eliminate air pockets in the entire system as long as it remains closed. Puke tanks just need a hose from the rad neck to the top of the puke tank. Coolant recovery tanks need the same hose, but the hose must connect to a line in the tank that goes to the bottom of the tank so it remains submerged in coolant all the time. The coolant recovery system also requires a rad cap that will allow coolant to run from the recovery tank back to the rad ( through a vent in the cap ) as the coolant cools. - and thats too cool or two COOLS Don't know why more racers don't use the closed ( coolant recovery ) system?

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Thanks everyone for your help. I will try jacking the front end up and see if I can get any bubbles and air pockets out. The only reason this was even posted was the car was running about 8-10 degrees hotter than last year (last year it was hard to get it above 160 degrees and this year it would run about 170). We are going to the track tomorrow night. I will let everyone know whether the additional water and trying to purge the air has any effect.

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You guys gonna hang around for Sat this time?

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Just to clearify things a bit, we are talking about 2 different systems here. An overflow bottle is just that. When the coolant heats up and expands, fluid dumps in to the top of the overflow bottle ( IE. puke tank ). What ever is lost from the rad, stays lost - and that space is replaced by air. If you have a big enough cooling system, no problem. The other system imploys a "coolant recovery" tank. When coolant heats up and expands, it dumps in to the coolant recovery tank, When it cools back down, it is drawn back in to the rad, thus keeping the rad full to the top of the filler neck. Benefit: You utilize all of the rad. You lose very little coolant over time. You eliminate air pockets in the entire system as long as it remains closed. Puke tanks just need a hose from the rad neck to the top of the puke tank. Coolant recovery tanks need the same hose, but the hose must connect to a line in the tank that goes to the bottom of the tank so it remains submerged in coolant all the time. The coolant recovery system also requires a rad cap that will allow coolant to run from the recovery tank back to the rad ( through a vent in the cap ) as the coolant cools. - and thats too cool or two COOLS Don't know why more racers don't use the closed ( coolant recovery ) system?

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To add to this.... each system has a different style
of cap... a recovery style cap has a disc that will
dangle down when held in the normal upright position...
a NON recovery cap does NOT have it dangling down...
that disc opens when the coolant isnt closing it and
as the engine/radiator is cooling it draws a vac
which pulls the coolant back in from the recovery tank

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Actually, that little metal disc that Bill is referring to should not be dangling down. If it is, the spring that holds it against the rubber rad neck seal is broken. You won't be able to build pressure in the system and you could blow coolant out the vent in the coolant recovery bottle - or puke tank. Dump the cap for a new one if yours dangles . Vacuum created in the system as the coolant cools will pull that little disc off the rubber seal and allow coolant to flow fron the tank to the rad. Almost all caps sold these days are ment to be used with coolant recovery systems. You will be hard pressed to find a cap without the little disc in it. BTW, a cap ment for coolant recovery systems will work just fine with the old puke tank system - but not the other way around.