water circulates inside the block when running. There is a bypass hose usually at the front (or rear in the case of the bx's), that's where it bypasses, recirculates until the t-stat opens. Most engines have something like that. Some have it built into the water pump housing or front cover. I don't remember on the 782's and 902's which they have, and I'm not going out to the shop to look right now.