Miatav8,MstrASE,A&P,F wrote:
I hear what you are saying Chuck and agree that it is best practice to put the upper neck at least as high as the top row, but it can be bled without a hole in the top of the rad. From empty,the system is filled through the expansion tank to minimum, the engine is started to start the pump which fills the pocket due to it's capacity and the delta p across the core, the system is topped, and the cap is installed. The rad would need to create a vacuum to drop the coolant out of the top of the rad.
Many oems have the upper neck lower than the top row as a compromise and no bleed port. 90s Ford explorer and ranger, 02 camaro/firebird, s10, and 02 celica to name a few. The most severe I've seen is the 96 olds achieva but they added a bleed port to that one.
On the oil coolers, the temp differential is much greater between ambient air and the oil than the coolant so the potential temp reduction is much greater plus the radiator capacity is not diminished as much by having to cool the oil too. It will preheat air across the rad if the cooler is mounted directly in front of the rad.
I agree with your description, if the delta P in the rad core is high enough to raise the input tank level to the top. I could see a situation where the core flow is less restricted and there might be air trapped. Who knows what really is happening? Of all the OEM radiators that I have seen (I googled cross flow radiators and looked at >100 different ones), I didn't see any on where the I/O ports were mid height and opposite each other. All were with the input at >80% high and the output was @ <20% height, forcing the full use of the rad core and evacuating any trapped air in the radiator as you mentioned.
I am no expert in automotive cooling, but understand some of the physics. Best Practices often are not implemented. Good Enough seems to work most of the time.
_________________
Chuck.
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