I have a FED with a VW radiator and a remote water pump and I am having trouble keeping water in the system. It has a SBC with a weiand 144 and the fill neck is at the manafold, I will fill the cooling system and let the pump circulate till full after I made a pass the temp never got over 210 and the overflow can was full. I figured that was just the extra after expansion and left it alone, after second pass on the way back to the trailer the temp gauge would sit around 205 then jump clear up then back down like it was low on water and my overflow was full again and it took 3 bottles of water to get the water level to just be able to see it at the bottom of the neck on the intake. I put a new #20 cap on and let it warm up and it puked a little out then stayed so I figured I was good then made a pass and overflow was full again. any ideas what I'm doing wrong?

You may have lost a head gasket.

^^^ Yep, you are pushing compression into the coolant. Head gasket or head issue. If its a return style overflow it should suck the coolant back when it cools off. If it doesn't then you have pressure still in the system. Fought this a few years ago with a porous head.

Exact same thing happened to me when I cracked two cylinders. I found it by removing spark plugs and turning it over. Water came pouring out of the spark plug hole of the cracked cylinders.

Tony, what fill neck are you using ? I had an issue with cap not going far enough down in CSR filler neck on mine. Had to go thru 5 caps that would seal correctly against base, inside.
Mine would fill the overflow tank in a few minutes, driving to lanes.
a 25 lb cap finally fixed it.

If it was from expansion only then it would only push a certain amount over then it would stay at that level. If it keeps pushing more and more over then like stated above head gasket. I would pull the plugs and use air in each cylinder with cooling system full and cap off and see if it starts bubbling. This will tell which cylinder is the culprit also.

Barring any head/gasket issues, You have any fans on your radiator. I know its open body, but still..... 2 Of the guys i race with have alterds,
Both run fans. One is a lay down radiator, the other is up rite.

Thanks for the feed back, the radiator lays flat and has a fan on it, I have used a couple different caps and feel like they are sealing up good the last cap I put on was a 28-31 on the crs fill neck then found out the screw on cap on the radiator was a #20 lol. I will defanetly check into the head gasket

I suspect you are have a compression leak into the coolant system, However it could also be that you are not getting all the air out of the system by the way you are filling the system.

This^^^^^! Dude knows his stuff

I used a radiator pressure check pump and pumped it to 20psi and it held it for 30 miniuts till I released it. I then fired it up again with the gauge on ant it started building psi past 20#. My question is if it's a head gasket wouldn't it loose psi when I pumped it up and let it sit with the tester?

I had a similar issue once that turned out to be a cracked cylinder head. The crack was hidden under a valve seat.

You could have a small leak that takes more than 20 psi to push water through. If that is the case, pressurizing the cooling system won't show anything, but air will get pushed through from cylinder pressure in excess of 20 psi, when the engine is running.