I've fought a over heating problem since I got my 28 sedan running. I'll give you all the low down and maybe somebody can think of something I haven't. 427 BBC, 425 HP square port heads, fresh rebuild, block was decked, heads have had a clean up cut on them. Hyd roller, tunnel ram with 2 600 Holleys, brand new alum water pump, clockwise rotation, 160 new thermostat, ended up cutting the center out and trying that, didn't help. Large electric fan with shroud, even took it off and installed a manual 17 inch with a full shroud didn't help. I had a stainless screen in front of rad, took it out, I have standard size pullies, not under driven. First new water pump leaked, tried a moroso I had and then bought this one that is supposed to move coolant 40% better. I can drive it or just let it run for 15 minutes and all at once it starts creeping up and in no time it's on 240, plus it takes forever to cool down. When I had the electric fan, I'd let the fan run for 10 minutes to cool what was in the rad and restart it. The temp wouldn't drop at all. Normally it should drop at least 20 degrees. I thought maybe I had installed Mark V head gaskets by mistake, grabbing at straws now, so I pulled the heads and it had the right gaskets. They are felpro and run over a $100 a pair. The weird thing was the heads wasn't stuck, they slid off like nothing, I don't even have to clean the block or heads. Also there was coolant droplets all over the surface and I drained the block on each side before I tore it down. You could wipe the gaskets off and almost pass them off as new ones. This is the car in my aviator, open, no hood and it also has a 3 core champion rad, brand new. Sorry for such a drawed out post but htis thing is driving me crazy, the only time it will loose coolant is if it pukes out the over flow and I run a pressure test, it held 15 psi for 30 minutes and didn't drop.. Timing has been at anywhere from 30 to 42 total, at 42 it runs the best and even if it's 200 degrees it starts soon as you hit the key. So if there is anything I'm missing, please speak up, I'd like to drive this thing.