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4 chevys and a ford
614 Posts
Discussion Starter · #1 ·
Im wondering if anyone has tried this for access to the cooling system;

Id like to add two brass ball valves to the system. Three way valves that can be spliced in.
So I can redirect flow out of the engine, and add coolant into the flow.
Maybe an inlet on the way back to the water pump from the heater core, and an outlet where the coolant leaves the engine, heading to the heater core.
Is that something anyone has tried?
Could that be a way to exchange coolant?
Im wondering if it would even be sufficient flow? Or would you just be able to capture some coolant, because its not a single circuit?
Im trying to understand coolant flow. Its not a single path is it? With the heater core open, does only some coolant flow through, while the rest circulates through
the engine/pump rad?
When the therm is open, does some coolant still bypass, back into the pump? Probably, i'm guessing.
Maybe someone can enlighten me on which way coolant flows. Specifically, i'm working on a 99 5.3 vortec.

15,316 Posts
The factory designs (sizes) the components around the heater bypass. The bypass is intended to provide sufficient flow through the engine when it is cold and before the thermostat opens such that the typical hot spots of exhaust valve seats and spark plug bosses receive sufficient coolant so as not to overheat and go into nucleate boiling. This drys the immediate surface allowing it to overheat which leads to cracks in the casting. This has nothing to do with bulk coolant temps the gauge reads, this is what happens in micro climate zones inside the engine but mostly around exhaust seats and spark plug bosses. One doesn’t need to take too many engines apart before discovering the results from this.

The heater in this circuit is simply a convince to the cabin designer to pick off hot coolant for cabin warming. Given this recirculating coolant is the first to get warm it speeds getting hot air from the heater which otherwise would wait for the entire bulk of the coolant to get hot enough to produce usable occupant heat.

The return is also used within the engine to dampen the temperature gradient of coolant entering the engine after the thermostat is open so as not to shock the front most cylinders with icy cold coolant off the radiator. The LT1 and 4 took a lesson from highway and heavy equipment engines to use a double thermostat one for hot return the other for cold intake to feed a mixer that holds the return coolant in a very tight temperature range so the engine coolant temperature is more uniform throughout the engine. This has a big effect on getting more uniform power from each cylinder. Where the typical auto engine over cools the front most cylinders and under cools the rear most. So in comparison the standard passenger car with a simple bypass while performing a similar function to the upper end engine’s coolant mixer, it is much cruder in design and function.

To the end of a steady state bypass the radiator is designed for this, where problems start to occur is with aging or modification to the radiator that has the effect of reducing heat transfer, then you get overheating problems.

Typically for air condition models the factory uses a three way valve to stop coolant flow to the heater core but maintain the bypass in that condition. This is done to take the heater core heat load off the A/C equipment thus allowing a smaller A/C system.

As for using ball valves to manually achieve this except for the inconvenience of having to reconfigure them to changes in the weather, there is no reason such a set up wouldn’t work.


More for Less Racer
20,941 Posts
Since it isn't a single circuit, you can't just open one valve to pump out all the old while introducing all the new through another valve at the heater lines.

Since the engine block just becomes a big mixer bowl basically, there is no way you can do a simple in/out complete fluid change in any way other than dump it all via radiator drain or lower rad hose removal, flush until clear, and add new coolant.
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