It's definitely not the cap. I put back my factory cap and didn't get a leak. I also changed the overflow hose. However, when the pressure built up, coolant was spilling out of the top of the overflow bottle. Does this mean the seal is bad where the metal pipe goes in the coolant bottle? I will get some black silicone and seal it up. Hopefully that fixes it. I also had a lot of coolant in the bottle, more than full hot so I'll take some of it out too.

 

i tried a metal cap on mine and it never did work right. had to order a stock one.

 

I am not an LT1 owner, but I have read some comments about the thermostat installation not going well if it is replaced with a wrong type or is mistakenly installed backwards. I guess that is due to the reverse flow making that a common mistake. Perhaps the original thermostat was defective and the new one is either the wrong type or in backwards?
http://shbox.com/1/tstat.jpg
You could try removing it and see if that helps.

 

I didn't know there was a wrong way to put in a thermostat. I just thought you put it in and away you go? I checked AllData and there's no mention of positioning the thermostat a certain way?


I did however find the culprit I believe! The overflow metal pipe that goes into the coolant bottle was broken right at the 90 degree bend. So, having the system not closed at that point would most likely cause the issues I was having with coolant leaking from the cap. I got a replacement hose and I'll put it on today. Hopefully that fixes it! I'll let you guys know!

 

I seem to remember the conversations going about putting the SBC thermostat in backwards. So if you used the wrong one, that was possible as well.

You can try asking Injuneer at camaroz28.com. He was the source of the information that I vaguely remember (probably wrongly;-)

Any way, Good luck today.

 

Alright, I fixed the coolant overflow hose. However I still have coolant pouring out of my cap when the pressure builds up UGH! This happens after the thermostat opens so I know the thermostat is working right.


Now, I have a lot of coolant in my overflow. I'm trying to figure out a way to syphon it out. I've changed the rad cap. Does anyone have any idea what could be causing this?


Here's a video of it right after I shut off the car:

 

Just in case you have the same radiator as this guy, check this topic. Make sure to read to the bottom.
5.7 cooling problem - Firebird Nation

 

Thanks for the link GaryDoug. I also think it's my radiator neck. It's a plastic neck and the cap I used was metal. The radiator is a year old. I replaced it last summer. I only drive it in summer. Over time taking it off and on it made some scoring. I will see what I can do to make a better seal on the cap.

 

yep thats what it looks like, neck is cracked or damaged.

 

If you look at my first post in this thread, I posted a video. At operating temp the cap would actually pop. This was before I replaced my water pump and thermostat. I'm wondering if that popping somehow damaged the radiator neck and stopped it from sealing properly. I don't have the popping anymore, just the leaking.