I have a question, how does the water circulate in a GMC 270 or 302 engine? I'm putting a turbo on a 270 and its water cooled. So does the water flow through the block then up through the head and on into the radiator through the thermostat? I need to catch the water, thinking at the rear of the head (pipe plug on top at the rear) plumb through the turbo then out to the water neck where the temp sender is below the thermostat. I'm wondering if that will have good circulation? Or should one go in above the thermostat? Also my wastegate is water cooled but its minimal. Jay D.
Last edited by Gdads51; 03/15/20259:48 PM. Reason: add detail to title
Water circulates as you said above. Rear of the head is near the hottest point in the system. 270 and 302 engines in some large trucks had a "bypass" tube from through top rear of the head to the engine side of the thermostat housing to provide extra water flow in the rear of the head. It also prevents the air pocket that occurs in that area when the coolant is changed.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Picture below is of the cylinder 6 of the 2193983 head that came to me on my military 302. That casting number was also used on 302 engines from 1952-62.
The fitting with the green tape on it is where the "bypassed" coolant leaves the head and travels through a metal tube to the bottom side of the thermostat housing. The "boss" (hope that's the right word) in the head for the fitting is in all the GMC heads that I've seen (even my 228), but is is not drilled and tapped for the fitting.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
thanks, my head is taped for pipe threads. so i think i will come out of the rear of the head and into the turbo. then back out of the turbo to the inlet in the water neck just below the thermostat. that should create a good flow of coolant i hope!! NOW i need to find coolant for the wastage, its also water cooled. i thought about just running it inline with the turbo, but its very restrictive only like a 3/16 hole in it for circulation. thought it might be to restrictive for the turbo flow. there is a plug on the block at the rear no. 6 cyl. could i get water from there and dump it in the thermostat neck also?? Jay D.
The plug on the block driver's side low near cylinder 6 usually has a drain cock in it. Water would be fairly cool as it hasn't been to the head since it left the radiator.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
so i'm thinking the outlet on the passenger side of the thermostat housing is for the hot or return for the heater? where does the other line from the heater go?? Jay D.
The water flows from the thermostat housing to the heater then to the water pump. The bypass tube goes to a tee off the thermostat housing then down to an elbow on the water pump (by-pass).
