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Yer might put a clutch fan on thanksIs this an eBay rad set up? If yes, there lies your problems. The clutch fan pulls a stack more air than cheap twin thermos. Plus those eBay alloy rads if that's what you have are not great. I installed one in my V6 and even though it held more water it didn't perform like I thought it would.
If you're dead set on thermos then you will need some that can pull a lot more air than those you have and you will probably need to upgrade the alternator to cope.