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Topic Review (Newest First)
07-12-2019 04:24 AM
55 Tony I shrunk my bypass fittings and hose down to about 3/8" for that reason. Didn't seem to make any difference in cooling, but I don't have a cooling problem either.
07-11-2019 05:06 PM
billbuch
BBC Bypass Feature

Someone mentioned the bypass on a BBC earlier in this thread. Some folks plug the intake outlet and the water pump inlet in hopes of decreasing the likelihood of overheating in traffic on a hot summer day. All things being equal, plugging those holes does force most if not all the hot coolant into the radiator. You'd be amazed at how much water moves through that little BBC bypass hose, and none of it goes into the radiator to shed its heat. It goes right back into the engine just as hot as when it came out. What must be done when plugging that bypass is to replace the stock t-stat with one that has 3 3/16" holes in the top hat of the t-stat (or drill those holes yourself in a stock high flow t-stat). Stewart Components offers those drilled t-stats. Those will hold back enough coolant to bring the motor's operating temp up quicker. Of course the t-stat will fully open when the motor's temp causes it to do so, and ALL the water will enter the radiator. I run a 454 BBC in my '32 Ford roadster and a 502 BBC in my '41 Willys, both of which have those modifications. Never had an overheating problem in either, and I reside in a hellhole called Texas.
07-09-2019 01:38 PM
Tim C Some engines leave the bypass open all the time, like said above a small amount of coolant may flow but not enough to make any difference, since most will take the path of least resistance, the large radiator hose.

Some newer engines block off the bypass, that's what the extra spring loaded disc below the thermostat is for. If the thermostat is closed the disc allows coolant to flow through the bypass. As the stat opens the disc pushes against the bypass opening and seals it off.

One engine that will get a lot of folks in trouble is the old Ford 351c, 351m, or 400s. They will take what looks like the same stat as every other Ford engine or even the Chevy small blocks, but there is a bypass port just below it, and the correct stat has a small brass "top hat" on the part of the thermostat that contains the wax that moves it open and closed. If you use the regular stat it'll idle fine but run hot at speed because the open bypass only let's the coolant flow around the front two cylinders. The correct stat the top hat goes into the bypass port to close it and causes the coolant to circulate properly.
07-09-2019 11:34 AM
ogre obviously with the thermostat closed the coolant just circulates thru the motor
thermostats open as heat hits circulates around the bottom of the thermostat
it can open 0 to 100%, varies according to temps

07-08-2019 01:57 PM
BogiesAnnex1 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
07-08-2019 01:23 PM
BogiesAnnex1
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
07-08-2019 12:30 PM
64nailhead
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.
07-07-2019 08:06 PM
RWENUTS 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.
07-07-2019 07:54 PM
Timtbss308 [emoji106]

Sent from my SM-G965U using Tapatalk
07-07-2019 07:39 PM
briansansone
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.

Sent from my SM-G965U using Tapatalk
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/
Thanks
07-07-2019 07:36 PM
briansansone 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
07-07-2019 05:51 AM
55 Tony 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.
07-06-2019 09:59 PM
Timtbss308 Follows least path of resistance because the other hose is much larger. Does still circulate through the bypass also though.

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07-06-2019 09:58 PM
johnsongrass1 The pump has the bypass in it.
It’s a 1/2 passage so water goes through it all the time.
07-06-2019 09:07 PM
briansansone 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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