'90 Silverado, Coolant flow thru engine and heater core


I have a 1990 1500 Silverado, 350 EFI engine, automatic trans, 220k miles on it. The truck has been slow to heat up enough to get heat out of the heater. The originally the heater core hoses were connected to the intake manifold and the radiator. Flow of coolant for the heater core was; Intake Manifold – Heater Core – Radiator – Water Pump – Engine/Intake Manifold. This configuration seemed to dictate heating of the coolant in the left radiator tank before hot water would be circulated thru the heater core. So I moved the heater hose that was connected to the radiator to a port on top of the water pump. This helped to get SOME hot water to the heater core sooner but the degree of heat that comes from the heater does not seem reflect what I think I should be getting once the engine is up to operating temp. (195 deg). I looked everywhere I could think to look for a diagram that shows coolant flow thru the engine and heater core and maybe even showing expected relative pressures. I’d like to find out if the coolant pressure at the intake manifold heater hose port is less than/greater than/or nearly equal to the connect on the water pump. I know I’ve seen heater hoses connected to these locations on other engines so I don’t know why this wouldn’t work better than it does. I know there is no obstruction in the heater hoses or heater core and there is no heat control valve to be a source of the problem and the heat/air diverter door is working properly. Do you know if the pressures at these two ports are too close for this to work right? Is there a diagram that will show me what I’m looking for?

Do you
have the same problem?
Friday, December 8th, 2006 AT 3:29 PM

1 Reply


Check the thermostat. It may be stuck open. Or try a slightly hotter one for winter use. There is no heat control valve?Most vehicles should have one.

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Friday, December 8th, 2006 AT 8:20 PM

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