Ls swap coolant system help

[sherm6413]

Ive searched threads and cannot find a specific answer I'm looking for. Its a 2003 5.3 in a 69 swb. just finished installing harness from bp, ls motor, and harness for truck from aaw, all is well, mostly, as it starts up runs fine has plenty of fuel and oil pressure. My problem is my radiator overflow starts pouring out antifreeze once it gets up temp around 190 and yes my fan is kicking on like its supposed to be. Do I need an overflow tank or "surge" tank as ive read about? My radiator is a crossflow from speedway. Should I just plug my overflow or add a tank it can blow in to? Help please

[Daaaanz67]

Was this your initial start up? I read some where that without a surge tank one should fill through the upper radiator hose on initial because the location of the t stat on these engines an air pocket is developed and cause over heat or the problem you are having. Surge tanks allow the air to travel backup to it on fill up. Basically burping the system. My 69 with 4.8 was filled through the upper rad hose on initial fill with no problems no surge tank at all.

[sherm6413]

Interesting I didn't know that, yes initial startup, but I've already filled it now .....

[SoMsippi_B-tie]

I filled my block thru the upper hose and then filled the radiator. Left the cap off radiator and let engine warm up, thermostat opened, fans running, and coolant flowing, shut it down, and put the cap on the radiator. No coolant overflow or surge tank.

[mongocanfly]

Does your water temp climb rapidly to the 190 mark if it does then you probably have a air pocket in the engine and its not circulating...I've done a couple of the swaps and the only way I can get them to circulate is to fill the engine thru the top radiator hose. I would say not to plug the overflow/bypass,,you may create a radiator bomb,, its there for a reason..add the tank if you have to.

[sherm6413]

Thanks guys , some stuff to try anyhow!

[crazy longhorn]

Where I crack the steam line, is at the top hose.....no top tank, but I do agree with Mongo......air in the system longhorn

[sherm6413]

So since I already have filled, should I from here, take top hose off , fill up until full then proceed.. To start and leave cap off radiator and keep topping off? Thanks guys

[mongocanfly]

The way I did mine was remove top hose from radiator, , fill radiator full,,put cap back on,, then holding up the top hose fill the engine full reattach hose,, mine has a overflow tank on it so I added some in there as well. From there I just cranked it up and let it idle until it got up to temp and thermostat opened,, you can tell for sure it opens when top hose suddenly gets hot,, fans kicked on,, I made sure I didn't have any leaks so I drove it down the road,, let it cool down then checked radiator level..if I didn't do it this way the water temps would climb very fast and it wouldnt circulate due to air pocket in engine..

[crazy longhorn]

Its like a sore dick.....you just cant beat it....well you could, but it would hurt! Crapp, I think I will get into trouble, on this one.....all jokes gone, yes I do beleive that you have air in the system....Longhorn