The Thermostat Housing Functions

[Dynomite]

Some Thoughts regarding the Thermostat Housing:
1. It does not make any difference if you use a 160 deg thermostat or 180 deg thermostat....they both are fully open at 185 deg.
2. I makes no difference if you drill small 1/8" holes in the thermostat flange as the additional flow area (.0123 square inches) is only 1.5% increase per hole over the Thermostat Full Open area of .785 square inches.
3. The Heater Circuit is open at all times even on a cool engine after start as the heater will be the first to get warm coolant.
4. On a very cold day with the heater on and Interior Fans set at Ten, the Heater Core with significant coolant flow could cool the engine for a significant amount of time before the main temperature controlled end of the Thermostat on the radiator side opens. The engine coolant mixed with some air would still expand into the radiator and to the coolant over flow below the passenger headlight.
5. If you want to cool your engine below the temperature controlled thermostat on a cold day or cool your engine a bit more on a very hot day, run your Heater with Interior Fans set at Ten using Outside Air (not recirculate) with windows open. The additional Coolant Flow through the Heater could be as high as 14% of the total coolant flow with 3/8 inch ID Heater Hoses.
6. The bottom of the thermostat on engine side opens at differential pressure of 5psi when open 1/2 inch allowing coolant to bypass the radiator (Marc Haibeck Testing).
7. When the thermostat has not reached opening temperature (175 deg) the coolant recirculates through the bottom of the thermostat at a pressure of 5psi since the coolant flow through the radiator is blocked.
8. Always use original green coolant GM 1825M.

Heater Hose Connection on Thermostat Housing

See Item #2 Replacing the Heater Core and Heater Hose Connection




See Item #8 The 180 deg versus the 160 deg thermostat or no thermostat

[QB93Z]

Thank you for the detailed analysis. You have laid to rest some mis-conceptions about the coolant system.

Using the heater to cool the engine when you are stuck in traffic on a hot day has saved me from over heating the engine many times. It makes the people uncomfortable but it might save the engine.

Turning off the AC when the engine temperature is too high will also help the situation because the air passing through the radiator is not pre-heated by the AC Condenser.

Jim

[Dynomite]

Originally Posted by QB93Z

Turning off the AC when the engine temperature is too high will also help the situation because the air passing through the radiator is not pre-heated by the AC Condenser.

Jim

Excellent observation........yes....with AC on and Interior Fans set at Ten the AC Condenser will heat up with the air passing through the AC Condenser also passing through the radiator resulting in less engine cooling by the radiator

[QB93Z]

In your drawing, you show the coolant flow path from the Injector Housing Coolant Manifolds to the Hot side heater hose and mention the "Recycled Coolant opens at 5psi over pressure". That feature is a small disc and spring on the "back" of the thermostat. The disc is what creates a differential pressure across the heater so that there will be flow. That disk has a notch (opening) in it so that there is always some coolant flow in the system. I believe that notch will affect the engine temperature at low engine rpm and low car speed.

Jim

[Dynomite]

Originally Posted by QB93Z

In your drawing, you show the coolant flow path from the Injector Housing Coolant Manifolds to the Hot side heater hose and mention the "Recycled Coolant opens at 5psi over pressure". That feature is a small disc and spring on the "back" of the thermostat. The disc is what creates a differential pressure across the heater so that there will be flow. That disk has a notch (opening) in it so that there is always some coolant flow in the system. I believe that notch will affect the engine temperature at low engine rpm and low car speed.

Jim

Yes....I calculate the notch areas to be about the same area as heater hose area or about 14% of full Thermostat open area. Each of two notches being about 1/4 inch x 1/4 inch. That disc does create the differential pressure to force hot coolant through the Heater Core. According to Marc's test the differential pressure created by the disc is 5psi at a disc opening of 1/2 inch.

As some may not know.....that disc is what keeps the radiator pressure at acceptable limits at high rpm. As the head loss through the radiator and thermostat increases with coolant flow the disc will open further at pressures over 5psi to a point that coolant recirculating flow path is completely open. You do not want to operate in that condition at very high rpms on HOT days as the coolant flow passing through the radiator is diminished compared to coolant flow recirculating (actually more coolant flow through radiator because of higher water pump flow but more coolant recirculating within the engine which overall is less engine cooling).