Do you know if AM3 coolers will fit on the new AM4 socket?
The answer is Yes and No. Those coolers that use the standard motherboard provided mounting bracket will work. But if the cooler comes with a custom backplate for attaching the cooler it will not work unless the company offers a new bracket for the AM4 socket. The mounting holes for the backplate on the AM4 socket are in a different place than they were on the AM2/AM3/AM3+ it is a slight difference but enough to make all the mounting kits for those coolers incompatible with AM4.
Do you know if AM3 coolers will fit on the new AM4 socket?
The answer is Yes and No. Those coolers that use the standard motherboard provided mounting bracket will work. But if the cooler comes with a custom backplate for attaching the cooler it will not work unless the company offers a new bracket for the AM4 socket. The mounting holes for the backplate on the AM4 socket are in a different place than they were on the AM2/AM3/AM3+ it is a slight difference but enough to make all the mounting kits for those coolers incompatible with AM4.