I've had to replace the cam and lifters in my 455. Installed SS headers. It overheats. I have replaced; Aluminum radiator, hoses, Water pump. Ive tried no thermostat, 180 and a 195. Added electric fans and shroud. I've tried retarding the timing somewhat. AFR is 14 at idle. Any suggestions would be appreciated. Thanks.

What was the original fluid like when you drained the system? Rusty brown? Did you try a backflush? forcefully running the fluid in the wrong direction? Might have to do some looking to find a shop that still does this. Did you notice any jelly like substance in the pan? Last time I rebuilt my motor the heads were completely plugged with JELLO after sitting for a couple years. Now we all know NOT to mix antifreeze, this is why. But I didn't mix.....oh I did use water wetter. Additive that reduces overall temp 20 degree's + and it did work. RED or green can't mix. Can mix or Justa use Yellow that mixes with all. There are cleaners you add and run then change fluid. Or use this to backflush. If you were using stock type fan, Flexalite fans move more air then a jet airplane. OK ya get what I mean. Run em in both my cars. $35-$40. Last, is there anything mixed with your oil?.....Headgasket? If it was overheated bad, that's one of the side effects. Good luck, let us know what you find out. You might be able to pass on the knowledge to someone else. That's how we roll round here.

Thanks. The fluid was clean. No gunk anywhere. 8500 miles on the engine when a lifter failed.

Water pump !

Check it’s backing plate clearance

We have had discussions about them before

As Kiwi has said, also you said you replaced the water pump already, what type of impeller is on the new pump? Most inexpensive rebuilds use a stamped impeller, they do not work well in a Pontiac engine makeing 300hp or more. If it has stamped impeller I would sugest replacing it with one with a cast impeller, check the spacing on the backing plate, and I would replace at least the seals on the transfer tubes, if not the transfer tubes also. after 50 years the parts do wear out.

Also what year timiong chain cover oare you running? I see you car is a 65, a 455 would come with the last Pontiac timingchain cover and water pump design, 69-79. The later design does flow more coolant.

Other tings to consider

1 - Does your radiator have a shround installed?

2- If so how far in does the fan stick in the shroud?

3 - what type of fan are you running?

make sure the water pump sleeves are in and the rubber is in good condition. easily left out.

Thanks everyone. I tried an electric water pump. 36 gpm. Didn't help. New aluminum high flow water pump with sleeves and backing plate. I went from a horizontal 2 wide tube aluminum radiator to a vertical 4 tube. I'm going back to the two tube today and see if it makes a difference. BTW, 4 tube has built in trans cooler, 4 tube does not.