Last year I installed a 383 sbc in place of the cadillac 472 that blew up in my 65 Chevy truck. The heater has not worked since and its getting cold here again so I need to figure out why. Here is what I have done/checked. Heater core is newer and has no restriction in it water flows easily through it. Water pump is new and the motor runs between 190 and 215 degrees in any situation. The heater hoses are hooked up the same way as on the cad motor. The system is bled of air pockets. Water pulled off the top of the intake manifold and returned to the side of the block where the drain plug would go. I tried routing 1 heater line from the front of the manifold and the other returning to the rear of the manifold. Nothing helps. If you let the engine idle long enough you can feel some warmth through the heater vents. So it almost seems as if the coolant is not really flowing through the heater core. The radiator does not have a provision for a heater line to return there. Anyone have any ideas? Thanks Blair

remove the return line from the heater core to make sure its really getting the flow, with the truck/car running and a constant water feed to the radiator (this is to prevent it from loosing to much water) you should be able to find out if its really getting the flow, also check your vacume lines, if one is off of the valve for opening and closing the heater core line you wont get much heat

I had a similar problem many years ago in a Range Rover.

Winter came and I needed the heater, but nothing came out. The engine was running normal temp and everything seemed ok. I flushed the system and the heater circuit was fine.

Eventually, the second time I removed the water pump, I noticed that the impellor wasn't as tight on the shaft as it should have been, and when the engine got to temp the pump shaft was spinning but the resistance of the water was enough to stop the impellor.

A new pump fixed it.

Dave

Yeah I did your first check and with the return off it runs plenty of water. Its when I hook it back up to the block (or wherever) that it seems to not flow. As for vacuum valves this thing is so old and primitive that it doesn't have any valves to shut off the water flow so it can't be that. Thanks though!

If there is no valve to shut the water flow to the core there must be a flap in the heater unit to stop the air from going through the core. Need to control the temp somehow. Only two things can be happening, either there is no hot water through the core or no air through the core and into the cab.:smokin:

If there is no valve to shut the water flow to the core there must be a flap in the heater unit to stop the air from going through the core. Need to control the temp somehow. Only two things can be happening, either there is no hot water through the core or no air through the core and into the cab.:smokin:


Yes I agree. But what I need some help with is the coolant flow path. I know the heater part works fine its just not getting the right flow of coolant. Can anyone comment on the best way to plumb a small block chevy cause somehow I think mine is screwed up. Thanks

On my sbc that was in a toy chassis, I hooked one heater hose to the water pump, (mine had a port coming out of the pass side) and the other heater hose to the top front port on the intake manifold. The heater worked very well this way.

Ok thats one variation I have not tried. I will hook it up that way and see what happens. Thanks

sounds like you may be running the water from the cooler side of the radiator rather than the hot side. Need to make sure the water running to the heater core is hot. if it's cool ie coming from the bottom of the radiator after it has cooled the air will not be hot.

yes you need to run a hose from a presureised area to a lesser presureised area.

ei.
water pump-core-intake
water pump-core-rad
water pump-core-block
intake-core-rad
block-core-rad

intake-core-block is like blowing on 2 starws into a sealed container. blow on one straw and water will spurt out the other, blow on both and you wont have any flow, preasure but no flow.