Got your email and thought I would respond here-
When I had my sbc with the Fiero 5 speed I only had the 2 rear Griffin rads in the back with Spal fans plus 1 electric waterpump on the motor and one in between the 2 rads and it cooled great. Now with my LS4 it was cooling just fine but once I added a/c and now a turbo it was having trouble staying at 180 degrees in heavy traffic during hot days. It would also get hot if I was driving it hard, it would climb up to 200-210 and not ever come back done until I stopped the car and let it cool back down.
I like this car to run no more than 180 degrees, the heat soak thru the cabin just gets too much even with Fatmat everywhere. What I have done is put a intercooler (like people use for turbos) between the rear cabin firewall and the motor down a little bit low with 2 small 7" electric fans. This is the one I used:
http://www.ebay.com/itm/140584269021?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649I hooked it up to my heater core lines (dont need a heater in the summer) and wired the 2 small fans to a couple relays and have it coming on via my brake light switch. That way it only comes on when Im sitting in traffic/stop light/ect basicly when my airflow is low. Plus I have a master switch/button that I can turn it on at anytime I need, but havnt needed to yet. I run a 180 degree thermostat with a small 1/4ish" hole drilled in it, my car will run 160ish degrees in the mornings when its cool outside (fans are set to come on at 160) and never over 185 in heat no matter how I drive it. I just tried to take a pic of this small rad/intercooler but it was too dark, I will take one tomorrow. I no longer run the 2nd electric waterpump only the factory LS4 waterpump, but I might hook up the 2nd inline electric waterpump to my intercooler/rad thing if I see it starting to run any warmer once the Texas 105+ degrees summers kick in.
Depending on how much money you want to spend you could change to 2 rear mounted rads, I might provide better cooling but personaly I would just keep the front mount for now.
I didnt read all the responces to your post but this is what I would do if it were my car:
A: First find someone who has a temperture gun, go over everything. Check to see if the rad/each cylinder/different parts of the motor to make sure there isnt a big temperture difference.
B: Get a second temp gauge (harbor friengt has them around $15.00) put into the motor somewhere, either the heads or intake. You will have to remove a plug somewhere to do this. When I first put in my sbc it was running hot, but come to find out the temperture sending unit wasnt the right one for my gauge.
If none of that works-
#1. Make sure I got a real good rad up front, made for a V8, preferable a aluminum rad.
#2. When the car is cold (not started that day) I would jack up the car on the waterpump side of the as high as I could get it. Remove the the thermostat housing and the thermostat, fill the motor thru the hole in the intake as much as you can.
#3. remove the rad cap and fill as much as you can, till the coolant starts coming out of the thermostat hole in the intake..
#4. Let it sit for 30 minutes and refill again while the car is still jacked up.
#5. Put back the thermostat and housing and rad cap, get your water hose turn it on a little and fill the upper hose as much as you can and quickly attach it to the thermostat housing. Try to get as much coolant/water in the the hose to get in the cooling system.
For sure you need to put that electric fan on the back of the rad, make sure the fan is turning the right way. You should be able to put a piece of heavy cardboard on the front of the rad and the electric fan should hold the cardboard in place while on.
I couldnt tell from your description what kind of waterpump you have, electric or belt driven. But if your running a electric waterpump- Make sure you have good 12v to the pump. Make sure its wired to come on with the key. And make sure there is a small hole drilled into the thermostat so coolant can pass thru even if the thermostat is closed. Drop the car off the jack and take it for a test drive.
If you have a belt driven water pump- I would go ahead and change it out to a good name brand performance high volume water pump. Cant hurt... Another thing to check is the wiring on the fan itself. you want a heavy gauge wire for the main power feed. Sometimes people/builders will use smaller wire and a cheap relay for the fan... You also need to check the airway to the rad, making sure you have good, unblocked airflow directly to the rad. Second you need to make sure the air has a good way of getting out. Airflow in and OUT is super important. Its best if you have some kind of wind deflector on the bottom of the rad to push air upto the rad.
If all this fails to improve your cooling, next do a leak down test on the motor to check for a bad head gasket. Also with the car running check the back of the exhaust to make sure no kind of moisture is comming out.
After you do all these test/replacing/checking and your still over heating get back to me and I will try to come up with something else.
