Time for an update including an important fundamental understanding of how the factory thermostat works in LS motors.
So I've been chasing an electrolysis issue which wiped out my AFCO radiator. It was still functional but had a pinhole leak that would show up after a track day or other high heat event.
Since I haven't fully cured my electrolysis but wanted a new radiator before this weekend's Optima event I bought the cheapest one I could find. The Griffin 8-00009-LS from Summit.
A couple of notes about the radiator.
- Has the 23" core but very narrow tanks so the driver's side mounts in the SBC location
- core isn't as centered in the core support openeing as the AFCO was
- Claims to use the correct sized inlets & outlets but the lower hose uses a 1.5" outlet where the AFCO used 1.25" I think factory on a lot of LS cars is actually 1.25"
- Core is about .5" taller than my old AFCO
The narrower side tanks also caused the outlets to move slightly and required new hoses. After several trips to the auto parts stores I finally found hoses I could cut and make fit without resorting to the universal hoses. I used the following:
Lower - Gates 21585
Upper - Dayco 71576 (length code D)
I also took this opportunity to install the 75-79 Chevy Nova coolant recovery tank in the passenger fender. Learned about this from Vince on this site. The older I get the more I appreciate function over form. I was tired of my billet tank which I could never accurately tell how full it was and it was catch can style rather than recovery. I wanted something I could see the level at a glance. Here is the pic Vince shared. I haven't taken one of my own set up yet but it looks pretty much the same.
So once I got everything mounted I thought I was chasing an air bubble due to low coolant flow at idle. This had happened to me before where at low engine speed the car would run warmer. This is regardless of vehicle speed or the fan being on/off. Rev up the engine and it would cool right down.
Well after lots of research online I stumbled on a bunch of threads at LS1tech.com talking about the need to have coolant flow through the heater hoses because that is how the thermostat senses when to open. Because the LS thermostat is on the lower radiator hose but has the sensing component on the back side of the thermostat it won't open based on the temp of the coolant coming from the radiator. The Factory Thermostat has a "bypass valve" on the back side of it that will allow hot engine coolant to hit the backside of the thermostat when it opens but the reading I've done online says this only opens with 5+ PSI of pressure. This would explain why at idle my car hits 210* and stays there but as soon as I blip the throttle it would drop below 200* fairly quickly. That blip of the throttle is likely opening the bypass valve which allows hot coolant to wash across the back of the thermostat and triggers the thermostat to open more fully.
The bypass valve on the back of the t-stat looks like this:
To test this I got the car nice and hot and then switched my heater valve open and within in a few minutes I could notice a huge difference in the behavior of the thermostat. Watching the coolant flow from the upper radiator hose I could see the Thermostat opening at a lower ECT and opening much farther (saw a lot more flow). I could actually see the temps cycle consistently.
Here is a video of the the behavior of temps with the valve open and then the valve closed all at idle with a fully warmed up engine (oil temps over 200* too).
Final note. This issue runs 50/50 on LS1tech.com between those who claim you can't block the heater ports and those who have blocked off the heater ports and notice no problems. But if you are ever fighting low engine speed/idle temps this might be one to check out.