What do consider overheating? You haven't told us yet, is it boiling over, or what temp are you getting, and where and how are you getting the temp reading?
A temp of 200-220 is not high for a idling engine.
First, go back to a 180 or 190 thermostat: Beleive it or not, your radiator fluid needs to be exposed to the radiator itself for it to cool, and a 160 will allow the fluid to flow thru the radiator core without the real time it takes to radiate the heat from the fluid as it flows thru the rad And yes, a 180 will not open to about 200, thats normal
Also, I really doubt the heat prob, if you really have one now, was, or is now caused now but the recent rebuild: Again, if the coolant system is good to go, you should not exp. overheating
The problem, at least to me, can only lie in four areas:
1. Radiator: I'm not a big fan of aluminum radiators. Frankly, for a mild build big block, there is not need for one, and the stock original rad did the job just fine. I have never had luck with an aluminum radiator cooling as well as a stock one, just me
2. Shroud: You need one
3. Coolant flow: Ensure there is no blockage or constriction anywhere in the coolant circuit: Anywhere in the block, heads, radiator or hoses
4. Timing (maybe) But if your engine is "running good" that prob isnt a factor
If indeed the rebuild is the cuase, you have a serious prob outside of the coolant system
Finally, I dont use a temp IR gun to see if I have a cooling prob. Get a reliable temp gauge, preferable digital, and get the reading from where it should be: from the temp sensor in the block Again, anything reading 220 at idle is just fine
First, lets go back to basics:
Let us know what you consider "overheating" in temps: If it really is high (to me above 220 at idle)
Put the 180 or maybe a 190 stat back on
Try a shroud
If no joy, try a stock radiator
\\Again, what temp reading do you consider "overheating"
