Which heater hose nipple goes where? 5/8 in the intake or water pump? My car seems have both 3/4.

can never remember either, at least without looking at it.... but... The "upper" on the heater core goes to the water pump, should be able to match it up from that.

If this is for a big block (guessing from your handle), there's two 3/4 on the water pump, one to the core, one to the short bypass hose into the front of the intake. then the 5/8 goes into the top of the intake.

Jim's memory is correct though. The top nipple on the heater core is 3/4 and gets hose from the pump, and the lower nipple on the core is 5/8 and goes to the intake.

From what I remember the 3/4 on the heater core is the inlet side. If that is true the intake fitting seems like it's a water exit since it is by the thermosthat and the lower is an intake since it is next to the lower radiator hose. Looks confusing.

If I understand what you wrote correctly, you are thinking backward. The water pump suction is the lower hose. The upper hose is the return to the radiator.

Here's a big block routing. Small block would be the same, minus the bypass hose.

http://img.photobucket.com/albums/v239/ekammerer/Orig_396_underhood_1.jpg

Thanks Eric. :beers: In other words the hoses should criss cross.