Pic of my fans. Having a hard time getting these sized correctly. As you can see, dual fans, shroud looks good. I think I still have air in the system. Last night I jacked up the front end and ran the engine, this is the first time the lower hose was as hot as the top hose.

Better pic of the shroud...

Took my car to a local rod shop. They hooked it up to an air lift and they have all of the air out of the coolant system now. They also drilled a small hole in the thermostat? Not sure what that will do, but he said it is running nice and cool now. Thanks for all the help. You guys prevented me from pulling my water pump and doing a ton of unnecessary work.

hole in the t stat body will help release trapped air from behind it. Its an ole school trick.

Remember, if you are ever unsure what your tech is doing please exercise your right to know and ask.

Glad you got it sorted out!

My question is --- did they find air in the system?? From your post I assume they did...


So the small hole in the thermostat was a trick that even some OEM manufacturers did ("high performance thermostats") - but in "most" older motors (SBC and BBC etc) the thermostats where the high point in the system... AIR wants to rise.

The LS thermostat location is LOW.... so unless the air was pushed thru the system to the thermostat - it would be pretty useless IMHO - but certainly doesn't hurt anything.

Regardless of all that -- I'm glad you think you now have it sorted out and it wasn't that big of a deal.

Greg, they did find air in the system. Everything is working as it should now. Chad, thanks for getting me on the right track. Revving to 2000 rpm and seeing the temp drop let me know that I had either air in the system or a weak water pump. Your input on your experiences prevented me from wasting time on pulling the pump etc. So, free beer to all who posted on this thread. SEMA???

I've been struggling with this one myself and so I drilled a small hole in the thermostat(I actually drilled a hole in each section as the LS1 has 2 flat areas that change with the temp). Seems to work fine now but will know for certain after a track day of course! Thanks for posting a real problem and seeing it through.

That was an old school trick to solve for pump cavation.... in other words - it was a bypass to allow some water to flow but also for air to be able to escape. Back in the day the cooling systems weren't "closed" like they are today.

Not saying this isn't something you can do... just saying there was a reason behind it "back in the day". The LS motors have the "steam vents" that are recirculated into the flow.. and the system should be closed to atmosphere via the use of the overflow can. That can should have enough coolant in it to cover the input - and be able to expand and contract without exposing the input tube. When cold - the input tube should be covered with coolant so that it doesn't draw air in as the motor cools down.


The other thing I've seen -- is the use of a radiator design where the return (to the radiator) hose inlet is near the radiator cap. There's a lot of pressure on that cap when the system is in full flow mode!