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-   -   Big Block By-Pass (http://www.hotrodders.com/forum/big-block-pass-115774.html)

waykoe 05-10-2007 12:50 PM

Big Block By-Pass
 
I'm in the middle of changing the water pump on my 454 BB Chevy. Is it nessesary to run the by-pass hose? I would like to leave it off. It's ugly and a pain to put on. Would this cause any problems and why is there in the first place. The new pump is a long style aluminum pump. I do not run a heater. What can I do to make this work? The car, a 65 Shelby Cobra, is only for cruising and good looks. Need help fast. This is an Edelbrock pump. Wayne

oldbogie 05-10-2007 01:51 PM

The bypass prevents pump cavitation when the thermostat is closed and it allows water circulation inside the cooling passages preventing steam pocket formation before the thermostat opens.

Eliminating this hose risks pump life as cavitation shakes the daylights out of the impeller, shaft and bearing. Steam pocket formation allows local overheating, mostly of and around the exhaust valves with heat stress cracking of the castings, possible loss of hard seat inserts if the heads are aluminum, and reduced valve life because of overheating being some outcomes.

It may be small, it may be ugly, but it is important.

Bogie

waykoe 05-10-2007 07:23 PM

Oldbogie, This is not good news. If remove the thermostat that will only cause other problems! I read someplace that you can drill small 1/8" holes in the thermostat housing to help this by-pass problem. Is this true or just an "old wives tale"? Thanks for the fast reply Oldbogie.
Wayne

Classix_Lover 05-10-2007 07:42 PM

Quote:

Originally Posted by waykoe
Oldbogie, This is not good news. If remove the thermostat that will only cause other problems! I read someplace that you can drill small 1/8" holes in the thermostat housing to help this by-pass problem. Is this true or just an "old wives tale"? Thanks for the fast reply Oldbogie.
Wayne

I heard that was mainly for helping to bleed any unecessary air from the system.

Bryan59EC 05-10-2007 07:47 PM

I have tried with it off, holes drilled in the t-stat, >>>overheat in 10 minutes unless I open the heater valve.>>>>>close valve, car overheats again.

Leave it on

Bryan

matt167 05-10-2007 07:47 PM

yep, just lets air out. some stat's are pre drilled with them

CptKaos 05-10-2007 08:20 PM

I run a 496 with 11 to 1 comp, aluminum pump and no bypass hose with no problems.

Larry

Classix_Lover 05-10-2007 08:25 PM

Quote:

Originally Posted by CptKaos
I run a 496 with 11 to 1 comp, aluminum pump and no bypass hose with no problems.

Larry

Lucky bastard... :D

CptKaos 05-10-2007 08:43 PM

the bypass hoses job is to let warm water flow to the heater core before the thermostat opens, that is all, no magic, no mystery.

Larry

Bryan59EC 05-11-2007 06:06 AM

That is what I thought too----
My 454 will overheat without it
Another gent on this board (in the same city as me) has a 454 that will run okay without but also has a 396 that has to have it :confused: .

When I ran a cooler T-stat with holes drilled----it got hot>>cooled down>>heated up>>>cooled down, several times before settling to an even temp.

With the bypass and a hotter t-stat/no holes---the car will warm up to temp and stay right there----no up and downs.

Bryan

BBCMudbogger 05-11-2007 09:42 AM

gotta love a guy who puts a big chevy in a Ford!!!!!!!!!!!!!!!

oldbogie 05-11-2007 10:32 AM

Quote:

Originally Posted by waykoe
Oldbogie, This is not good news. If remove the thermostat that will only cause other problems! I read someplace that you can drill small 1/8" holes in the thermostat housing to help this by-pass problem. Is this true or just an "old wives tale"? Thanks for the fast reply Oldbogie.
Wayne

You can eliminate the hose and provide a by-pass by drilling a couple small holes in the thermostat. This will provide a bleed of coolant which will allow a little circulation. As long as you don't start to wind the revs up before the motor is warmed to the point where the thermostat is opening, this would be OK. The other side effect is the leak past the thermostat to the radiator will increase the time for warm up.

I would think that a couple/three 1/8th holes would do it.

Bogie

k-star 05-11-2007 10:49 AM

by pass
 
I also run big blocks with-out the by pass hose and have zero issues with it.. You do need the 1/8" holes in the t-stat..

One big reason for most cars that over heat is incorrect ignition timing... I would bet that the big blocks that have heating issues do not have enough timing on them.

Keith

oldbogie 05-11-2007 12:09 PM

Quote:

Originally Posted by k-star
I also run big blocks with-out the by pass hose and have zero issues with it.. You do need the 1/8" holes in the t-stat..

One big reason for most cars that over heat is incorrect ignition timing... I would bet that the big blocks that have heating issues do not have enough timing on them.

Keith

Here's whats going on, or not, inside an engine with out any form of coolant return when the thermostat is closed. Coolant is not circulating! Therefore, the pump is in cavitation which aerates the coolant and causes vibrations of the impeller, it's shaft, bearing and seal that they are not designed for. This increases the potential for failure of these components, which you see as reduced life not so much a catastrophe like the pump blowing off the front of the engine or something exciting like that. More likely the seal suddenly leaks on a holiday weekend when you're a hundred and fifty miles from home. This might me more of an engineers than mechanics issue where engineers worry about things that might be where mechanics worry about things that are. Who knows? If your going to do this you probably should know whether your water pump has a metal or plastic impeller. I'd bet on metal putting up with cavitation for a longer period, but transferring more of the forces to the shaft, bearing and seal. Plastic probably absorbs more punishment without secondary transfer of forces, but won't do it for long. The second big issue with no by-pass during closed thermostat is no coolant flow in the block and heads. This means localized hot spots form around the usual super hot places which is the exhaust valves and seats. This forms steam pockets and steam is not a very good conductor of heat, therefore, the metal in these areas gets very hot and expands. Expansion against colder adjacent metal results in cracked castings for cast iron and will often allow the hard seat insert of an aluminum head to fall out, now that's a real mess. In any casting the valve seats will distort and the valves will leak gasses past these distortions. These results can be a bit expensive to repair.

These aren't just theoretical ramblings this is what's happening. The possibility of damage is a function of how often and how hard you push, all that does is establish when it does damage, nothing for if.

Now the fellow that started this thread stated he had no heater. The heater connection is also a coolant bypass when the thermostat is closed. So normal factory engines really have two bypasses, one being pump to block in the case of the BBC a hose to the manifold, the SBC uses a passage cast into the block and pump under the right side pump horn. The second is the heater core circuit which routes from various places on the engine to various schemes to the intake side of the water pump. This may be to the pump itself or to the cool tank side of the radiator or into a fitting in the coolant pump inlet hose. All of these are used by different years on different models. So if your system includes a heater, you also have a bypass beside the crummy hose between the manifold and the water pump.

Now I've had a few Ford FE engines in my life and owning one of them really makes you insensitive to the whinnings of BBC owners. If you want a bypass that's ugly and is a real pain to repair when it fails, get yourself and FE (332, 352, 361, 390, 391, 406, 410, 427, 428) and find out what real hardship is!

Bogie

waykoe 05-13-2007 07:24 PM

k-star, Your right about the timing issue. If I have too much advance it will run hot when I run the engine past 3000 RPM, If I turn the timing back it will overheat in traffic. It took a long time to find out what was the best setup. I understand what Oldbogie is saying. This car is strickly a summertime car. No top, no side glass, a true roadster. Having said that, the car is driven only when the air temp is over 60 so cold starts and long warm-ups are not a problem. The cast iron pump went "south" because the car was not run for all most a year, a heart attack will do that to you. Now I'm ready for the summer. The by-pass hose (the one on my car) is more ugly than it's a pain. This is a hi- dollar pump and I'd like to get the most of the looks dept. or I would of got a stock replacment from Autozone. I have all ready collapsed the upper rad. hose once on warm up with the by-pass connected. I appreciate all the response. It all helps.

BBCMudbogger, If Chevy would not of had the Corvette, the Cobra WOULD of came with a Chevy.

Thanks everybody. Your all good people! Wayne


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