Lesson Learned: at least on my 1997 528i sedan, the radiator shroud can be removed, and replaced, with the fan still installed on the fan clutch. I had to replace a leaky thermostat housing/radiator hose connector on my 1997 528i sedan. RealOEM.com indicates that two different radiator options were available on this vehicle. Mine is the one with the separate overflow tank on the passenger side of the radiator.
To access the thermostat housing, the fan shroud and fan blades must be removed. The preferred procedure is to loosen and remove the fan clutch from the water pump, and then remove the shroud and fan together. Unfortunately, my fan clutch would not move when I tried to loosen it. The next alternate approach is to remove the three socket head cap screws (female hex drive in screw head) that holds the fan onto the clutch. They can be accessed if the shroud is lifted a few inches, and you can sneak in an allen wrench.
However, I could not spot those screws. They were there, I just could not find them for some reason. So, after a number of minutes and attempts, I incorrectly assumed that I had some different fan assembly with no screws to remove. So I had to remove the fan shroud with the fan still in place. Surprisingly, this can be done. The belly pan has to be removed, since one needs to get underneath to determine which way the shroud has to be shifted to clear about three obstacles on each side. If possible, remove the lower radiator hose from the radiator, to gain a fraction of an inch more clearance for the lower tabs on the shroud. The fan blades have to flex about 3mm to squeeze the shroud between the fan and the radiator, but gentle pressure accomplishes that. Then the shroud has to be shifted to one side, then angled a bit to get one tab past the various obstacles on the back or the radiator. Then the shroud has to be shifted to the other side, and tilted slightly again, to clear the obstacle on the other side.
It took me about ten minutes, with about a dozen trips under the car to view things from below, but the shroud finally slipped out. With the shroud removed, I finally found the three socket head cap screws, and remove the fan blades. I then attempted, for about an hour, to remove the clutch, since I now had better access.
I should point out that I had dripped penetrating oil on the fan clutch fitting the night before, and had added more during my attempts to loosen it, with no luck. I confess that I did not have the special tool to hold the fan pulley, but I did have a 32mm end wrench for the clutch. I applied a lot of pressure, with no success. I hit the wrench with a hammer a few times, attempting to shock it off. I was concerned about breaking off a water pump cover bolt. So then I applied heat. A Smith oxy/acetylene micro torch is my favorite thing for such efforts, since the flame is very small, but gets a lot of heat into a small space. Even with heat, penetrating oil, and great access, the fitting would not budge. I elected to leave the fan clutch in place, and replaced the thermostat, housing, and radiator hoses.
I figured that since I now knew where the socket head cap screws on the fan were, I would install the shroud with the fan blades partially, and then screw the fan blades to the clutch hub. I could not make that happen. I could not get the fan blades aligned on the clutch straight enough to start even the first screw. In retrospect, I might have been able to do it if I had used extra-long machine screws to align the fan on the hub, and then replace them one at a time with the correct, shorter, screws. It did not occur to me at the time. Instead, I decided to install the fan blades, and then slip the shroud back into place. I reasoned that I managed to get it out, so I should be able to get it back in. And I was right. It took a little longer to replace the shroud than to remove it – about 20 minutes. The main problem was that the lowest tab on side of the shroud on the driver’s side kept snapping down under a narrow lip on the side of the radiator core. I finally figured out that I had to be under the car with a long screwdriver to guide it onto the top (rearward, on the car) of that lip as it was sliding down. Since the radiator was empty, I also removed the lower radiator hose from the radiator, to get that extra 2mm of clearance. Then it was just a matter of fiddling with the shroud, and sneaking it past the fan into position.
I do not recommend this procedure. It would have been a lot easier if I could have removed the fan clutch. But the car is decades old, and this is a large diameter thread, which has probably corroded pretty badly. It could also be a good argument for not attempting this unless you have the special tool to hold the fan pulley in place while loosening the fan clutch.
I would also suggest that you purchase a replacement radiator drain plug if you are working on your cooling system. Mine snapped off when I re-installed it. I had not over-torqued it. It is a plastic M10x1.5 plug with a drain hole through its center. Mine was over twenty years old, had experience thousands of thermal cycles, and been immersed in coolant for all that time. It was weak when new, and got brittle and broke. That required drilling out the broken shaft and removing it with an EZ-Out. It was plastic and easy to drill, and the threads were in good shape, so it was not too hard. But, even though the plug is way overpriced (between $8 and $18, depending upon where you buy it), it should be replaced if you still have the original in place.
For what it is worth, I replaced the original plastic thermostat housing with an aluminum URO aftermarket unit. I was pleased with the quality of the casting and machining, and the fit was very good. The aluminum unit was actually cheaper than aftermarket polymer units (not the reason I bought metal), which surprised me.
Thank you Brian from Ohio for this insight!