If I'm interpreting you correctly...you're basically saying that the coolant is coming into the radiator at 236, and exiting at 200? And with the understanding that this is surface temp...meaning your actual coolant INSIDE the radiator at these locations is higher than that?

You can't cool an engine with 200+ degree coolant going INTO it! So I disagree entirely with whoever said "the radiator is obviously doing its job"....or maybe I am misunderstanding the location of your temp readings...a radiator that considers 200+ degree coolant to be "cooled" and ready to shove back into an engine is most certainly NOT doing its job...

But why?

Not sure what to tell you quite honestly...other than to check everything that all people are suggesting. Frankly I see the likelihood of you having more than one problem, and one feeds the other, which may be compounding the difficulty of finding a solution...like maybe it's running scary-lean and super hot, causing rapid engine temp increase, PLUS you have maybe inadequate OR too much coolant flow, PLUS a possible airflow problem thru the radiator. You may have a trifecta of issues here.

Your fan setup has me completely puzzled. I see little reason or benefit to a double fan setup like you describe, I'm even wondering if that added fan is really screwing with the airflow of the other fan, and creating some sort of strange, extremely unbalanced airflow that is causing some air to bypass many portions of the radiator. I can easily see how a setup you describe will cram all sorts of air thru the center of the radiator, which feeds plenty of air to your engine-mounted fan, which in turn prevents ANY air at all from passing thru the portions of the radiator core that are outside of your electric fan circle! Your second fan may very well be rendering a huge portion of your radiator core completely ineffective at cooling because no air is flowing thru the perimeter areas!

Have you tried a similar test with the electric fan disconnected? Or better yet fully removed? From one of your earlier comments I believe you did run it without this second fan...but want to confirm.

Your current 5 blade fan...what's the diameter? How fully does it fill your shroud? How is your spacing...fan usually should be about 50% inside the shroud, 50% out of the shroud, with reasonably tight clearance without rubbing. Big gaps between fan and shroud will cost a massive amount of airflow to skip by the radiator. Photos would be helpful here.

Let me also be first to admit out loud that I'm taking random shots in the dark here.