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Discussion Starter · #1 ·
OK. On a BB you have water (from the radiator) coming into the lower hose and into the water pump. The water pump is pumping water into the block, through the heads and ..............

If the thermostat is closed, a small portion of the water from the engine goes back (uncooled) into the pump where it is pumped back into the engine. This is a closed system but I can see that you might want to do this to reduce cavitation.

Here is the point that I get to that seems confusing. When the thermostat is open, isn't some portion of the heated water being reintroduced into the engine (through the bypass hose)? Sure seems like it would be better if all went through the radiator. :huh:

Paging Noonie
 

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Discussion Starter · #3 ·
That article describes how the bypass hose works and I can certainly see how it would help with cavitation when the thermostat was closed. When the thermostat is open, it seems like some percentage of the hot coolant that was just in your engine is being pumped back into your engine without having gone through the radiator.

I guess it all works out in the end. The combined (heated and cooled) fluid would eventually make it through the radiator.
 

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That article describes how the bypass hose works and I can certainly see how it would help with cavitation when the thermostat was closed. When the thermostat is open, it seems like some percentage of the hot coolant that was just in your engine is being pumped back into your engine without having gone through the radiator.

I guess it all works out in the end. The combined (heated and cooled) fluid would eventually make it through the radiator.
It ALSO states that if you drill holes in the stat mounting flange, the hose can be blocked off. Something Noonie and I both advocate. The Robertshaw stat also fails open. A nice feature.:thumbsup:
 

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The bypass function makes perfect sense to me while the engine is cold. It not only reduces cavitation, it helps promote even water temperature distribution during the warm up. I agree that it would be nice if the bypass function closed off when the thermostat opened, but it seems to me the small amount that gets recirculated is compensated for by the thermostat opening up a bit further to allow more coolant to flow into the radiator for cooling, thus compensating (temperature wise) for the uncooled portion.
I'll confess I'm not sold on the drilled thermostat and bypass hose delete method. This just seems to be a step backward in reducing warm up times.
 

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OK. On a BB you have water (from the radiator) coming into the lower hose and into the water pump. The water pump is pumping water into the block, through the heads and ..............

If the thermostat is closed, a small portion of the water from the engine goes back (uncooled) into the pump where it is pumped back into the engine. This is a closed system but I can see that you might want to do this to reduce cavitation.

Here is the point that I get to that seems confusing. When the thermostat is open, isn't some portion of the heated water being reintroduced into the engine (through the bypass hose)? Sure seems like it would be better if all went through the radiator. :huh:
Paging Noonie
You are absolutely right.

Just for kicks, sometime, take off the bypass hose at the manifold and run a few feet of heater hose over the fender, then fire up the motor and you will be amazed at how much coolant is being diverted back into the pump, whether or not the tstat is open.

For my location and temps, I always close off the bypass and use the pressure balanced full flow tstats with holes. Grant it , it rarely gets below 70° here and is usually above 85 or 90. The additional time it takes for warmup is only a few minutes. Tstat open for me is only 5 minutes.

The holes in the tstat really don't prevent cavitation, but do help in reducing hotspots before the tstat opens. Of course, you don't want to rev high when the engine is cold either. Pump cavitation at idle won't hurt anything.

A few weeks ago, I fired up an engine with the water pump off and could feel the water jacket side of the cylinder walls and also of the combustion chamber and after only 30 seconds of run time, the metal was so hot that I could no longer keep my finger on it. It heats up very fast.

A fair number of BB people run hotter than they would like to and this can be a viable solution.
First off I would use a Stewarts pump hands down. God only knows where and how well made even the GM branded pumps are these days and with Stewarts you know what you're getting.:D
 

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Discussion Starter · #7 ·
You are absolutely right.

Just for kicks, sometime, take off the bypass hose at the manifold and run a few feet of heater hose over the fender, then fire up the motor and you will be amazed at how much coolant is being diverted back into the pump, whether or not the tstat is open.

For my location and temps, I always close off the bypass and use the pressure balanced full flow tstats with holes. Grant it , it rarely gets below 70° here and is usually above 85 or 90. The additional time it takes for warmup is only a few minutes. Tstat open for me is only 5 minutes.

The holes in the tstat really don't prevent cavitation, but do help in reducing hotspots before the tstat opens. Of course, you don't want to rev high when the engine is cold either. Pump cavitation at idle won't hurt anything.

A few weeks ago, I fired up an engine with the water pump off and could feel the water jacket side of the cylinder walls and also of the combustion chamber and after only 30 seconds of run time, the metal was so hot that I could no longer keep my finger on it. It heats up very fast.

A fair number of BB people run hotter than they would like to and this can be a viable solution.
First off I would use a Stewarts pump hands down. God only knows where and how well made even the GM branded pumps are these days and with Stewarts you know what you're getting.:D
I guess I am having a hard time understanding how a couple of small holes in your thermostat could actually replace the bypass hose. It really seems like the flow rate (through the holes) would be an insignificant fraction of the flow rate that would be needed to eliminate/reduce cavitation at the pump.

Maybe in reality, the cavitation issue is overblown?
 

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I guess I am having a hard time understanding how a couple of small holes in your thermostat could actually replace the bypass hose. It really seems like the flow rate (through the holes) would be an insignificant fraction of the flow rate that would be needed to eliminate/reduce cavitation at the pump.

Maybe in reality, the cavitation issue is overblown?
My best guess. The cast in bypass holes in the SBC pump are only like 1/4". The size of the BBC bypass hose might be that large out of pure ease/availibilty of materials. A 1/4" rubber bypass hose would be structurally weak. :D
 

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I have not ran a bypass hose on my BB sense I first fired it. I also do not have the T stat drilled. I also removed all of my heating and AC stuff sense I am replacing it at a later date with an aftermarket system. So are you guys saying that I maybe running higher temps without the bypass or the holes drilled? I live in SC and we realy never get cold enough to worry about warm up time not to mention this is a 1 day a week good weather car so I don't really have to worry about warming it up. MY BB does run consistently between 200-210 with an Edelbrock WP, Dewitt radiator and spal fans.

Wade
 

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I have not ran a bypass hose on my BB sense I first fired it. I also do not have the T stat drilled. I also removed all of my heating and AC stuff sense I am replacing it at a later date with an aftermarket system. So are you guys saying that I maybe running higher temps without the bypass or the holes drilled? I live in SC and we realy never get cold enough to worry about warm up time not to mention this is a 1 day a week good weather car so I don't really have to worry about warming it up. MY BB does run consistently between 200-210 with an Edelbrock WP, Dewitt radiator and spal fans.

Wade
Results are all that matters. It works for your set-up. I would not lose sleep over it.
 

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An additional reason to keep the bypass hose: Reduced thermal shock. When the thermostat opens, and coolant then starts its circulation from the radiator, there is now a large supply of relatively cold water trying to come in contact with the hot metal surfaces internal to the block. As long as the bypass function is operable, this cold coolant will be diluted with hot coolant, reducing the thermal shock to the engine metal. This reduced thermal shock would seem to promote head gasket longevity.
 

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I guess I am having a hard time understanding how a couple of small holes in your thermostat could actually replace the bypass hose. It really seems like the flow rate (through the holes) would be an insignificant fraction of the flow rate that would be needed to eliminate/reduce cavitation at the pump.

Maybe in reality, the cavitation issue is overblown?
You're right again.:laughing:

As far as pumps go, these aren't very efficient and are designed to cavitate at times. Going from 650rpm to 6000rpm pretty well dictates that. It also has to be all things to all people that drive cars under all conditions. Pretty impossible.

The holes in the tstat are for 3 reasons.
-to eliminate trapped air when filling the system.
-when the bypass is closed off, it allows a little amount of circulation until the tstat opens so as not to create hotspots in the heads. It allows essentially the same purpose as the bypass, but when the tstat is open, no more bypass and more efficient cooling. The pump will cavitate, but it doesn't matter, because you shouldn't be revving until the tstat is open.
-the holes relieve a little pressure from the backside of the tstat to help it open easier.

It is also important to use a pressure balanced tstat such as the Robert Shaw when using a higher flow pump or bypass blockoff.
Even the Super Stants are not pressure balanced.

The Robert Shaw tstats are only 9 bucks at Advance Auto.:D
 

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Discussion Starter · #13 ·
You're right again.:laughing:

As far as pumps go, these aren't very efficient and are designed to cavitate at times. Going from 650rpm to 6000rpm pretty well dictates that. It also has to be all things to all people that drive cars under all conditions. Pretty impossible.

The holes in the tstat are for 3 reasons.
-to eliminate trapped air when filling the system.
-when the bypass is closed off, it allows a little amount of circulation until the tstat opens so as not to create hotspots in the heads. It allows essentially the same purpose as the bypass, but when the tstat is open, no more bypass and more efficient cooling. The pump will cavitate, but it doesn't matter, because you shouldn't be revving until the tstat is open.
-the holes relieve a little pressure from the backside of the tstat to help it open easier.

It is also important to use a pressure balanced tstat such as the Robert Shaw when using a higher flow pump or bypass blockoff.
Even the Super Stants are not pressure balanced.

The Robert Shaw tstats are only 9 bucks at Advance Auto.:D
Thanks for the info. One more question, how many holes and how big? Ok (I lied):laughing:, what does "pressure balanced" mean in reference to a thermostat?
 

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Thanks for the info. One more question, how many holes and how big? Ok (I lied):laughing:, what does "pressure balanced" mean in reference to a thermostat?
I use 1 - 1/8" hole if the bypass is still operational for filling purposes and 3 - 1/8" holes if it is closed.

Here is a pic from Stewart's site. Shows where to drill the hole in this type.





The standard tstats use a flat disc that is perpendicular to the flow of water, so the increased flow at rpm will tend to put more pressure on the disc in the direction to close it.

The RS tstat has the sleeve that opens and is parallel to the flow and position of the opening is such that the flow will help to open it more if anything, hence the term " pressure balanced".

The oem stuff was adequate for millions of cars for many years, this is just an improvement.
 
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