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Old 07-06-2019, 07:22 PM
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where does the coolant go?

I have always had questions on exactly how coolant circulates through an engine.

What happens before the thermostat opens?
If the coolant is pulled from the bottom of the radiator, but does not return to the top.... Whats going on. How does the coolant circulate around the engine
before it is allowed back to the radiator by an open thermostat?

I will be bypassing the rear heat on my chevy van, and I realized I dont quite know which way the coolant is moving through the various hoses.

Sounds like a beginners question, but I bet not all working mechanics know exactly the movement of coolant. I have never had a problem fixing anything
with a cooling system. I know the basics. But I realized if I look at any one
hose, like the little line coming out the top of the pump, I dont know what the purpose is , or which way the coolant is moving ( i assume its some type of bypass related to the flow with a closed thermostat. )

All right pros. Whats the deal?

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Old 07-06-2019, 07:55 PM
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Ignoring the oddball Chevy motors with reverse flow cooling, the water pump inlet is the lower radiator hose. Coolant flows rearward in the block and up into the head, then forward to the crossover at the front of the intake. If the t-stat is open, the coolant flows from there to the top of the radiator. When the t-stat is closed, the pump simply circulates the coolant already in the block in the same manner. The fact that the lower radiator hose is open to the pump doesn't mean that there is any flow in it. The closed t-stat prevents any flow in the radiator, so there is no flow out of the radiator into the pump either.

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Old 07-06-2019, 07:57 PM
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Except for the built in bypass.
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Old 07-06-2019, 08:46 PM
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The bypass is what completes the loop when the thermostat is closed.

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Old 07-06-2019, 09:07 PM
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Yup , I have the odd ball chevys . 3 of them.
Ive got me an old f150 too.

So with the Thermostat closed, there is no flow at the main inlet, and whatever
coolant is presented through bypass , goes back through the vanes and into he block.

When the thermostat opens, what makes the coolant empty to the radiator instead of just running through the bypass?
Pressure? Does some of the coolant run through the bypass, even when the thermostat is open? Or is the bypass, bypassed when the therm is open.

Thanks Yall
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Old 07-06-2019, 09:58 PM
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The pump has the bypass in it.
It’s a 1/2 passage so water goes through it all the time.
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Old 07-06-2019, 09:59 PM
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Follows least path of resistance because the other hose is much larger. Does still circulate through the bypass also though.

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Old 07-07-2019, 05:51 AM
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If it's a BBC the bypass in external with a short hose. When I first put mine together I didn't know what those ports were for and plugged them. The temp would go up and up until finally the t-stat opened. So I ran the heater hose in a loop. That worked until I learned about the bypass that I bypassed (did away with). Fixed that and everything worked smooth again.
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Old 07-07-2019, 07:36 PM
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Final Question. I see the light.

Im working on a 2001 chevy v6 vortec.

The pump has the main input, and 2 smaller connections on top.
It looks like the coolant leaves the intake by a hose that heads to the heater core, then to one of the small connections on the pump.

and the other small connection is a hose from the front of the intake. I assume thats the bypass?

Do those two small lines empty right into the vanes of the pump, and then into block again?

So all the tubes on the pump are inputs, and the only output is there at the block? I think I got it
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Old 07-07-2019, 07:39 PM
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Quote:
Originally Posted by Timtbss308 View Post
Follows least path of resistance because the other hose is much larger. Does still circulate through the bypass also though.

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Like electricity.
So it all works in tandem. its not one path this way, then switched that way when the therm opens. Its all flowing together. I think I can see it now/
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Old 07-07-2019, 07:54 PM
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Old 07-07-2019, 08:06 PM
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Yup!
The newer vortec motors don’t have the bypass in the block connected to a hole in the head. They use the bypass from the intake back to the water pump.
The water pumps are centrifugal type. The fluid is pulled into the vanes at the outside edge and discharge in the centre of the impeller.
The return line from the heater core sometimes goes to the rad instead.
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Old 07-08-2019, 12:30 PM
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Quote:
Originally Posted by RWENUTS View Post
Yup!
The newer vortec motors donít have the bypass in the block connected to a hole in the head. They use the bypass from the intake back to the water pump.
The water pumps are centrifugal type. The fluid is pulled into the vanes at the outside edge and discharge in the centre of the impeller.
The return line from the heater core sometimes goes to the rad instead.
Do these style pumps have the same exterior appearance? Asking due to I had an overcooling issue with a high mileage 4.3 that created a no cab heat condition in the winter. Restricting the coolant return from the heater core resolved the issue 'somewhat'. This motor was a 300K+ unit that was definitely not on the original or OEM waterpump. It looked the same as any SBC pump.
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Old 07-08-2019, 01:23 PM
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Quote:
Originally Posted by RWENUTS View Post
......The water pumps are centrifugal type. The fluid is pulled into the vanes at the outside edge and discharge in the centre of the impeller......
Actually this is backwards, fluid enters at the hub and is flung to the outside by the spinning impeller.

Bogie
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Old 07-08-2019, 01:57 PM
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To te OP.

Coolant is pulled from the bottom outlet of the radiator through the larger hose into the pump. The rotation of the impeller throws the fluid to the outer perimiter of the pumping chamber. In the case of a 4.3 Chevy V6, like the Gen I SBC it is derrived from the exit from the pump is by the two horns bolted to the block.

When the thermostat is closed to speed engine warm up the coolant in the block is recirculated using one of several types of bypass arraingements which do not cycle coolant through the radiator. So in this condition although the inlet hose from bottom of radiator to pump is not restricted, the return from engine to radiator at the top is stopped by the closed thermostat. The Gen I SBC form engines use a bypass thruogh the heater core or with AC a bypass valve that shuts off the heater core when the AC is operating and shunts the coolant through the valve back into the heater return line. The return line connects to a fitting on the pump that connects to an internal passage that feeds the impeller at its hub cavity. The pre 96 Vortec engines included a small balance bypass on the passenger side below the block feed hole intended to correct pump output that over feeds the passenger side bank with coolant with the clockwise turning pre serpentine pumps. This was eventually eliminated as the counterclockwise turning serpentine pump doesn't need it, but this is somewhat inconsistant with the 96 and 97 V8 engines. Generally the 4.3 moved into the Vortec changes a little earlier than the V8's so these are inconsistent in the 95 and 96 model years.

The SBC V6 and V8 have some variation in the return side of the bypass hose that range from connection at the pump to the radiators cold side tank (the side the pump bottom feeds from) or to a tee fitting in the lower hose.

The Vortec engines vary from the TBI engines in that the return is also used to feed heated coolant to the throttle body so there is some extra external plumbing. It is possible to substitute the 87 through 95 TBI pump and do some changes to the plumbing as that pump bolts up. If converted to vee belts the older long pump can be used but it is a very little different in length so belts don't exactly line up but unless you've got eagle eyes most people don't notice it.

Bogie
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