Guys, no I have not been running without a shroud the whole time, there is a long history to this issue and this is just the latest step. I just switched it to no shroud a couple days ago at the suggestion of some car buffs, they thought the aluminum shroud I was using was blocking too much airflow. I always had a shroud before.
In my road tests, shroud vs. no shroud has so far made almost no difference in heating up while moving. That's where the problem has been all along, heating up at speed. There was never an issue with idle or slow-speed heating up, and it doesn't overheat at idle or going slow now even with no shroud. The shroud is only there to help slow speed or idle cooling.
Dave, I looked into the possibility of running lean, the O2 sensors would seem to indicate that I'm not running lean, but I also changed the fuel filter in case it was clogged. Not sure what else to do for checking that, I could do a fuel pressure test but that is a PITA since there is no Schrader valve on the fuel rail (I thought my old one had one). To be honest, I would be really surprised if the engine would run lean enough to be this hot and NOT throw a code, this isn't an old carbureted engine, the computer is constantly monitoring the exhaust emissions to detect just such a thing and would throw a P0107 if it was lean.
Ok, so you are not using any shroud at all, remember it needs one to create some king of venturi effect to force the air through the radiators to make a good heat exchange for it to work, if you can force more air through a specific spot (radiator) then you should get what you need, ok if i'm not mistaken you no longer have the factory shroud, you need one to maintain a constant air flow thought the engine, idling or driving the combination of the thermostat and fan clutch is essential to keep any engine cool, if I'm not mistaken you have a Spal fan-pwm to be honest have never used one how do you know when and how much to adjust it while driving, and from what I saw on the pictures I don't think you had enough back spacing on the aluminum fan shroud.
The shroud doesn't create a venturi effect for the radiator, it's on the wrong side of the airflow to do that. Some cars do that with air scoops and such in the bumper or grill. The shroud is to help the fan work better and the fan is for idle and slow speed, nothing else.
If you don't believe me, start looking at the CFM ratings of some of the most powerful high-performance fans. Then do some simple math estimations, divide out the area of the fan blades from the CFM and get linear feet per minute, and convert to miles per hour. You'll find that you don't have to be driving very fast at all for the air hitting the front of the car to be much greater than what a fan would move.
