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Coolant Bypass on 454 BB Chevy

07/01/2010 6:12 PM

Is it neccessary to use the bypass from the front of the intake manifold to the top of the waterpump. Short curved hose. This is a '96 or newer stock BB in a streetrod. Don't know whether to hook up or not.

Tk's, jim, 33vicki

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#1

Re: coolant bypass on 454 BBchevy

07/01/2010 6:35 PM

Yes, I have a 1986 truck with a 454, I'm not positive this is a bypass, but it does circulate water through your manifold to assist in engine cooling, I wouldn't try to outsmart the people that designed it. It is a pain to put it on, I boil mine in water first to soften it up, then put a little dish soap on it. It'll slip right on.

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#2

Re: Coolant Bypass on 454 BB Chevy

07/02/2010 6:17 AM

Lets hope I get this right.

The purpose of the by-pass is to allow coolant to circulate through the engine before the thermostat opens. This allows you to heat the engine quicker and possibly obtain needed heat for the heater if you need heat in the winter. Once the thermostat opens, coolant is circulated mostly through the radiator and back to the engine. In certain circumstances where the outside temp is extremely low the engine would take much longer to heat up and not provide heat to the passenger compartment also it allows the coolant to circulate and prevent development of HOT SPOTS near the cylinders and heads with the help of the water pump. Would anyone care to add to this?

h

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#3
In reply to #2

Re: Coolant Bypass on 454 BB Chevy

07/02/2010 7:09 AM

I popped the hood yesterday after I posted. It's been awhile since I've had my engine apart. This has nothing to do with the heater core, just from my external visual, it looks like it provides a path of less resistance, than all coolant going through the thermostat. Since you seem determined to fight this, I have a factory manual for this engine, it covers everything, I will have a look and get back to you.

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#4
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Re: Coolant Bypass on 454 BB Chevy

07/02/2010 8:29 AM

It is a thermal bypass, and it is specific to the 7.4 l engine. I can't tell you precisely why it is there, but, it obviously runs into the coolant channels on your intake manifold. Since it is only on the 454, we can assume that some issue came up, in which they deemed it necessary. My educated guess would be that there may have been an issue with cracked/warped heads. If you think about it, that bypass would allow preheated coolant to mingle with cold coolant as the thermostat opens, allowing all of the coolant to warm gradually, rather than sending a rush of cold coolant to a hot engine all at once. To summarize, I can see absolutely no benefit to dismantling it, and potential problems if you do. Hope this helps.

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#10
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Re: Coolant Bypass on 454 BB Chevy

07/02/2010 11:11 PM

I don't believe it is unique to the BB Chevy. The system is present in some fashion on all engines I can think of. SB Chevy's have no separate bypass hose, but rout through the heaters core. But I am not sure why thay can use a heater control valve. Any one have any ideas?

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#13
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Re: Coolant Bypass on 454 BB Chevy

07/03/2010 4:52 AM

a rush of cold coolant to a hot engine all at once.??

Thermostats opens very gradually. h in 2 is right...preventing hotspots and cylinderhead cracking or headgasket failure.

jurie sa

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#16
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Re: Coolant Bypass on 454 BB Chevy

07/03/2010 12:10 PM

Not all of them. I've always tested thermostats in a pot of water before installing them. The newer ones do open gradually. But back when I first started doing this, I routinely got thermostats that would pop open all at once. I don't know if they all open gradually now or not. If they do, that was not always the case.

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#9
In reply to #2

Re: Coolant Bypass on 454 BB Chevy

07/02/2010 11:01 PM

You are correct.

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#17
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Re: Coolant Bypass on 454 BB Chevy

07/03/2010 12:14 PM

Ga, Sorry about that guest. It looked like I totally dismissed you. When your post came up, I thought it was the OP for some reason, and didn't give it a close enough read. Good job.

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#5

Re: Coolant Bypass on 454 BB Chevy

07/02/2010 10:03 AM

Thanks to both who replyed, I didn't mention that it is an aftermarket Edelbrock manifold. However the outlet is there in the front. My question stems from the fact that I had plumbed the heater directly to this outlet in the manifold and I hated to backtrack. I have yet to start this engine so now is the best time to make changes.

Based on your replys I will plumb as designed.

Thanks, Jim

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#6
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Re: Coolant Bypass on 454 BB Chevy

07/02/2010 3:46 PM

Hold on there. Is there not a heater connect just to the left of your thermostat cover. If not, I think you can have it both ways. Put in a hose connection on the right top of your water pump, as your looking at it from the front of the truck, run this to the inlet of your heater core, run the outlet of the heater core to the hole in the front of your manifold. Everything will be functioning as if you had that little nub of hose in place, you'll just have your heater in between. That won't pose any problem at all.

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#7
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Re: Coolant Bypass on 454 BB Chevy

07/02/2010 4:05 PM

I have to add though, that I try to keep everything as close to factory as possible, that way next time I'm in there I'm not trying to remember all of the little frankensteins I've created in there.

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#8
In reply to #5

Re: Coolant Bypass on 454 BB Chevy

07/02/2010 10:46 PM

As posted, the purpose of this is to allow water to circulate before the thermostat opens. There are a few ways to work with this. One is to block both ends, and use a flow restrictor in place of the thermostat. These are common in NASCAR. Another option is as posted to use the heater as a bypass for the thermostat. BUT, you can not use a heater control valve in that line. The last option I can think of is to leave the set up you have there, and run the hose from the top of the water pump to the unused manifold fitting that would have normally had the heater. Send pictures. Good luck.

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#12
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Re: Coolant Bypass on 454 BB Chevy

07/03/2010 1:34 AM

For street applications, I caution to not use a flow restrictor, or run without a thermostat. In race engines, the need is to keep coolant flowing so heat is always being transported away to be cooled. If a thermostat were installed, the water would "stagnate" and temperatures would rise and fall sharply. With all the severe thrashing about of the moving parts at the extremes of rpm, the last thing the engine wants to see is unnecessary cycling of expansion and contraction of the cylinder block and heads. There is plenty of constant air flow through the radiator to keep coolant race cars use only water with sometimes a heat transfer additive temperatures relatively constant, as long as it isn't restricted by a car in front spewing hot exhaust. When I used to ride, on a cool night I would look for a big car, Lincoln or Caddy was best, to follow to keep warm.

Street engines, with thermostats, need to have the coolant reside in the engine until it has absorbed sufficient heat to be removed and replaced by cooled fluid. The hot fluid then resides in the radiator to be cooled. In stop and go traffic, air flow is not constant, even with a fan, due to the variation of engine speeds from idling to going through the gears when accelerating. If there were not "stagnated" water in the radiator, coolant temperatures would keep rising until overheating occurred.

The bypass allows a small amount of water to move through to create movement of water in the block, enhancing the absorption of heat, while not greatly affecting the cooling of the coolant in the radiator. In some cars that do not have an obvious bypass, the thermostat may have a small hole in the valve plug/plate.

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#11
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Re: Coolant Bypass on 454 BB Chevy

07/03/2010 1:23 AM

I would stick with the original configuration for this by-pass hose. Reason if the by-pass is there to enable circulation of coolant from the upper cylinder areas before the thermostat opens why would you choose to create and uneven heating scenario in the upper cylinder area?

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#14
In reply to #5

Re: Coolant Bypass on 454 BB Chevy

07/03/2010 9:45 AM

On any car engine, and even big industrial diesel engines, there is what is called a Thermostatic Valve that allow the cooling water to go back into the engine block without passing through the cooling radiator. This is done at the start of a cold engine to accelerate the heating up of the engine to normal operating temperature for the particular engine. When that temperature is reached, the valve will snap or move gradually to close the bypass and send back the hot water to the radiator for cooling. The regulation and mixing of bypass water and radiator water allows the temperature of the engine to be controlled and kept within the narrow range that is best for the engine (reduce wear and tear etc...).

This valve and its bypass branch should never be removed especially in climates where the ambient temp are low (cold winters...). Since you are rigging a heater it means that the outside temp can be low in your area...therefore don't remove this bypass! Make sure it is working properly!

You need a heater and want to use the hot water from the engine, then tap the hoses as advised by previous entries.

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#15

Re: Coolant Bypass on 454 BB Chevy

07/03/2010 9:57 AM

Post number 2 has it real close. The main reason for the "bypass" is to circulate the water though the block at a sufficient volume to prevent hot spots. It is possible to have a real big efficient radiator that will slow the movement of water though the engine because the thermostat only "reads" the temperature of the water right under the thermister in the thermostat and still have hot areas in the cylinder heads that can lead to uneven cylinder to cylinder power, leaking head gaskets and finally cracking of the heads. You would also possibly notice rapid changes in gauge reading as the thermostat finally reads that the water is real hot and sends a charge of cool water through the engine and it cools of and then the thermostat again reads a cool engine and then the cycle begins again. And as someone else stated, all engines have this "bypass" in some fashion. The small block chevy has that small hole under the passenger side of the water pump that is hidden from view until you remove the water pump to see it, always check to be sure that those "bypass" holes are clear. I guess that the thing we refer to as a "bypass" is not really a "bypass" but a real NESSESARY part of the cooling system.......

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#18
In reply to #15

Re: Coolant Bypass on 454 BB Chevy

07/03/2010 12:44 PM

Thank you. I could not think of the system on the SB Chevy.

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#19

Re: Coolant Bypass on 454 BB Chevy

07/03/2010 11:02 PM

The pupose of the water flowing through the manifold spacer plate, between the carbeurator and the intake manifold is to heat the air-fuel vapor mixture for increased atomization. This was popular on the Quadra-jet, which had tiny primaries and HUGE secondaries. When the operator put his foot in the accelerator, a stream of fuel is injected into the secondary venturi for increased power. If the air-fuel mixture is not preheated, prior to passing into the combustion chamber, the engine floods and hesitates or stalls with a giant cloud of very black smoke. That's why you have to let the engine temperature stabilize, prior to accelerating. It was common, in the '60's to let the car stand at an idle, for about 5 minutes, prior to driving. It was called, "warming up the car."

This is not a by-pass, I repeat, "This is not a by-pass."

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#20
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Re: Coolant Bypass on 454 BB Chevy

07/04/2010 1:40 AM

I do not choose to reply to "guests" often. But For your post, I will make an exception.

I spent from 1971 till 1975 in GM dealerships. There were no water spacers used under Quadra-jets. Ford had EGR spacer plates for a number of years. There may have been a spread bore EGR spacer plate in the years that they used the Quadra-jet. But never water spacer plates.

If a Q-J had a bog it was because the choke pull off had a ruptured diaphragm in it, or the choke was not set properly. By design, the secondary throttle plates would not open until the choke system had fully opened. When the driver did put his foot into it before warm up, it would just act as a 2 bbl. After warm up and the choke was off, the throttle plates would open up as soon as the driver demanded more throttle. The air valves on the top were restricted by the choke pull off from opening faster than a restrictor in same would allow. Some even had a secondary choke pull off just to assure no bog. There was no accelerator pump on the second half of these carbs. As the AVS started to open, there would be vacuum at a point just in front of the upper blades. This vacuum would draw raw fuel from 2 separate wells that were designed specifically for this purpose.

You were wise to hide behind the "guest" posting after a post like that. Good day sir.

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#21
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Re: Coolant Bypass on 454 BB Chevy

07/04/2010 2:31 AM

I think you have the Q-Jet mixed up with the popular Widebeast V-9 of about the same time frame, about 1965 to 1988. these engines were used in the Phragalini, (proninced frag-A- leney), autos that were imported from Greenland for use in the cold weather areas of the good old USA. These cars failed to perform very well on American Gas. And they also had a cog wheel drive that required the road to have holes spaced exactly 3.75 inches apart all along the highway to have the necessary traction to propel the car down a slick highway. Of coarse the American road builders refused to punch the holes in the road surface and the rest is history. The carburetor they used was a W-Jet. This used frozen ice cubes to cause the choke to close in warm weather. Ice was hard to find in Death Valley on a warm day, rendering these cars useless on most places in the USA. Also when the driver put his foot in the carburetor it would and it would bite the drivers toes off. This was the days before OSHA and the EPA, so these occasional occurrences were pretty much overlooked. Oh, by the way the Phagalini's did not have a water pump "bypass".

Don't believe everything you read on the internet.......

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#23
In reply to #21

Re: Coolant Bypass on 454 BB Chevy

07/04/2010 1:22 PM

Right, I remember them, The spare tires for them were hard to inflate.

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#24
In reply to #19

Re: Coolant Bypass on 454 BB Chevy

07/05/2010 4:49 AM

Hi there quite an idea but you're confusing the spacer plate with a separator plate beneath the plenum

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#22

Re: Coolant Bypass on 454 BB Chevy

07/04/2010 11:36 AM

The bypass provides a continuos sample of the water from the block to the thermostat,allowing it to function more proportionately,provides heating of the intake manifold to prevent frosting of the intake due to evaporation of the fuel, prevents the pump from cavitating due to the closed thermostat, forcing it to open prematurely,and prevents damage to the impeller due to cavitation damage, provides water circulation to lubricate and cool the water pump seals,increases engine efficiency by warming the fuel(boiling point of gasoline is 195F), prevents hot-spots and premature wear of the back cylinders.Besides all of the above, it is not very important.

Remember this: A very important lesson I learned many years ago as an apprentice in a manufacturing plant:

You will not see a hole, a bolt, a flange,a lip or any other part of a machine that does not serve a function worthy of it's cost.It either is serving a current funtion, or served to assist the manufacture of the part.You may see an unused threaded hole, but it is there for an optional attachment, and it was cheaper to drill and tap than to set up a separate line for the operation for every option, (like air conditioner bracket holes in head and block).

Every piece of the machine was vetted for cost vs benefit before it was implemented into the manufacturing process.

It is too expensive to make a useless part.Therefore, I am very hesitant to bypass or modify an existing design until I have analysed all of it's functions.Most of the time,the original design has it right, but there are always a few exceptions to every rule, but for the majority of the time, in the last 40 years, my mentor has been right.

HTRN

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#25
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Re: Coolant Bypass on 454 BB Chevy

07/05/2010 5:11 AM

I agree with most of your post but please enlighten me of the path the coolant runs to and from the pump a full loop please something doesn't jive.

This by-pass as we've termed it exits the front center of the intake manifold directly to the water pump housing.

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#26
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Re: Coolant Bypass on 454 BB Chevy

07/05/2010 11:04 PM

The water pump is always pushing water into the front of the engine block at the lower part of the cylinders. The water flows around the cylinders and also up into the cylinder heads. From the cylinder heads it travels into the intake manifold, where it is blocked by the thermostat until it opens. Until that happens, water is able to travel through the bypass hose back into the suction area of the water pump. Is that easier to picture now?

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#27
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Re: Coolant Bypass on 454 BB Chevy

07/06/2010 7:09 AM

Thanks bob c,

yabadaba-doo

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