The 350 V-8 in my FJ40 had a Flex-a-lite #1316 16" Flex Fan installed with a 1" spacer. (Radiator is stock.) The cooling was OK, but the temp would go up when in heavy traffic or wheeling. I replaced it with a #1318 18" fan (actually 18-1/4"), and a 2" spacer. Now you can actually feel air being pulled through the front of the mesh grill at idle. Couldn't feel that before. And when driving you can hear the fan noise quick clearly as the fan sucks the air in. There's a noticable increase in airflow in the engine compartment at all RPMs, and you can feel a lot more air coming out of the hood vents. The 18" fan now covers the core area from top to bottom, and side to side. It only missed the corners. The 19" fan, #1319, which is actually 19-5/16", would almost completely cover the corners as well. I was really tempted to install this fan, and there is enough clearance for it. It does come close, though, to the stock radiator fill cap neck, about 1" away, while the 18" fan is 1" away and 1" down. I'm not sure if severe body flex could cause the 19" fan to ever hit the filler neck, so I finally weenied out and went with the 18" fan. Ran the FJ40 around today. It was slightly hotter out today than yesterday. The cruising temp was slightly better. But the idling and slow speed temp was much better. About a good 10 to 15 degrees better, because the temp would just climb. I'm not sure if the fan size was that significant. It's possible a 16" might have been adequate, but I don't like to do the job twice, so I swapped it out. I think the main culprit was that the fan was simply too far away from the radiator, and was pulling some air in from the sides. In other words, it was partially recirculating hot engine compartment air.