you may be flowing your antifreeze too fast through the half size. if your antifreeze moves slower through the radiator it will be cooler and cool better. the only way to fix this is to put a washer somewhere between the radiator and the engine. you can try different size washers until you find one that flows as much as it can but keeps the car cool.

small block chevrolets have problems like this when those stupid rich kids around here buy a $300 high flow electric water pump for their stock ls1.....
the restriction always fixes the problem.

 

It's an interesting concept. The b16a has a 22 tooth water pump though, which slows down the coolant movement as compared to the standard LS 19 tooth piece. I never had any issues with the radiator in previous setups, only this one. After a closer inspection of the cooling system though it would seem that the coolant wasn't flowing fast enough through the system, via a sticking t-stat that really wasn't that old. I've since replaced every piece in the cooling system, and today will be the trial as to how it goes once I fill and bleed out the system.

 

Is the manifold touching the radiator It should be at least a inch away.

Randy

 

Nope...it had at least 4" of clearance from where the downpipe was, and the mani was even further away than that. It still did all that crap even with a 2.5" bar and plate radiator. Only thing I came up with after a datalog was heatsoak...very very bad heatsoak...intake mani and fmic.