I have a GM 430 hp 5.7 (350) in my '37 Ford. GM recommends installing a bi-pass in the water pump circuit, but says to be sure you have the correct rotation pump "Bypass Hose and Plugs *Note: Before installing bypass hose be sure you have the correct rotation water pump installed on your engine. The correct water pump is supplied with the Serpentine Belt Accessory Drive Package. Install 1 bypass hose fitting into intake manifold and one into water pump. Take the supplied bypass hose and cut to size, to fit between the water pump and intake manifold fittings. Install bypass hose and secure with supplied hose clamps" I changed the pump to a short V belt type pump for fan clearance. I have a Vintage Air heater/AC with a control valve in the heater cifcuit. How critical is it to have the bypass. I've put about 1500 miles on the engine so far and haven't noticed any issues. Thanks for your input. Bill
bill3337
you would need the bypass to flow water while thermostat is closed, and purge air from system.
A v-belt pump is designed to rotate with engine direction, a serpentine will rotate opposite engine rotation, because it drives off the back side of belt. The impellers would be different.
A v-belt pump is designed to rotate with engine direction, a serpentine will rotate opposite engine rotation, because it drives off the back side of belt. The impellers would be different.
So does that mean I can't hook up a bypass, or that I need to hook it up differently? I've never noticed any issues when the engine is warming up.
The bypass serves to circulate coolant when the thermostat is closed. It is serving several functions.
- One, is by constantly recirculating coolant when the engine is cold the engine warms up faster.
- Two, this gets the moving parts to proper clearances sooner, if you're running forged pistons and aluminum bearings on the mains and rods this is big time important.
- Three, it gets the oil hot sooner which drives the waters of combustion blow by out reducing sludge and varnish buildups.
- Four, this provides fast cabin heat in cold weather.
- Five, the coolant circulation provides temperature control on the very hot spots like the exhaust valves and their seats and the spark plug bosses. This greatly reduces head cracks by caused by large heat profiles across small distances by providing a more uniform temperature profile between these very hot places and cooler places like the adjacent intake valve and seat.
- Six, as the thermostat opens the cooler coolant flowing in is diluted with the hot coolant preventing a larger engine wide thermal shock.
There are guys who argue that this is an unregulated hot coolant leak when the thermostat is open are missing the fact that the cooling system is sized with this “leak” in mind. I would proffer that if you are having heating problems the root cause is not the bypass circuit but somewhere else in the radiator sizing or the engine tune.
Bogie
- One, is by constantly recirculating coolant when the engine is cold the engine warms up faster.
- Two, this gets the moving parts to proper clearances sooner, if you're running forged pistons and aluminum bearings on the mains and rods this is big time important.
- Three, it gets the oil hot sooner which drives the waters of combustion blow by out reducing sludge and varnish buildups.
- Four, this provides fast cabin heat in cold weather.
- Five, the coolant circulation provides temperature control on the very hot spots like the exhaust valves and their seats and the spark plug bosses. This greatly reduces head cracks by caused by large heat profiles across small distances by providing a more uniform temperature profile between these very hot places and cooler places like the adjacent intake valve and seat.
- Six, as the thermostat opens the cooler coolant flowing in is diluted with the hot coolant preventing a larger engine wide thermal shock.
There are guys who argue that this is an unregulated hot coolant leak when the thermostat is open are missing the fact that the cooling system is sized with this “leak” in mind. I would proffer that if you are having heating problems the root cause is not the bypass circuit but somewhere else in the radiator sizing or the engine tune.
Bogie
Good information thanks. I haven't had any issues with overheating or any other symptoms as far as I can see. When I bought the crate motor from GM, there was nothing with it that mentioned a bypass, but found this information on line this week, while looking up some other facts.
A question often asked is how to plumb the bypass.
The bypass flows from a point of higher coolant pressure to a point of lower pressure. The engine side of the pump is under greater pressure than the radiator and pump inlet side.
A most common source of high pressure for the bypass is somewhere on the block, heads, or the return on the intake ahead of the thermostat. Where the intake is concerned GM has sourced typically from the back side of the intake from a fitting that sits over one of the head’s return ports. Another common place is at the coolant passage on the front that ties the returns of the left and right head together and is before the thermostat.
Hose from one of these points typically goes first to the heater core, but a summer hot rod might return without using a heater. The return architecture would be a hose coming from the heater core or directly from the manifold or other pressure source to the low pressure side of the pump or the radiator. Here typically the return is a fitting on the top of the pump that is internally cored with a passage to the impeller inlet. Other configurations you can run into is the return hose going to a fitting on the cold side tank of the radiator which is where the pump intake hose originates from whether this is a cross flow or down flow radiator. Another configuration you might see is a tee in the inlet hose to the pump. Here I’m talking the classic Chevy pump whether a short or long pump and whether it is of clockwise rotation typical of 1955 thru 1986 using V-belts or the counter clockwise rotation of 1987 thru 1995 using the factory serpentine belts. Note that there are aftermarket serpentine belt systems that use the clockwise turning pumps. Also, note the fan needs to match the direction of pump rotation if you are using a pump driven fan.
These pre-1996 engines use or have a small bypass hole under the right side (passenger side) mounting boss to the engine. This is cored up to the right side head using about a quarter inch hole. There are those that feel this bypass is sufficient without the external hose bypass, I’m not a supporter of this idea, it’s a pretty small hole compared to the hose diameters.
The 1996 L30, 305 and L31, 350 Vortecs use a different pump, though related to the 87-95 pump it has different ancillary passages that use the bypass coolant for other functions that earlier models do not, so unless you are using a full up L30 or L31 Vortec with its factory fuel injection these are not a pump you want for an earlier engine or a Vortec not using the factory EFI. Also, these things never being easy the 1996 block casting may or may not have the traditional internally cored bypass and for sure the 97 and up blocks it is gone. Now you can use these 96-2002 production and the Vortec crate block with the older pumps but if the internal passage is not there then you need to put a plug into the pump passage, a screw plug being the best answer.
This I know is big data dump, make a copy and put it in a book, if you start playing across the years of these engines, this info will make life a lot simpler. And this is just cooling system data; there’s crankshafts, seals, flat tapes or factory roller cam differences, carburetors to EFI and different types of EFI that drive a lot of other changes.
Bogie
The bypass flows from a point of higher coolant pressure to a point of lower pressure. The engine side of the pump is under greater pressure than the radiator and pump inlet side.
A most common source of high pressure for the bypass is somewhere on the block, heads, or the return on the intake ahead of the thermostat. Where the intake is concerned GM has sourced typically from the back side of the intake from a fitting that sits over one of the head’s return ports. Another common place is at the coolant passage on the front that ties the returns of the left and right head together and is before the thermostat.
Hose from one of these points typically goes first to the heater core, but a summer hot rod might return without using a heater. The return architecture would be a hose coming from the heater core or directly from the manifold or other pressure source to the low pressure side of the pump or the radiator. Here typically the return is a fitting on the top of the pump that is internally cored with a passage to the impeller inlet. Other configurations you can run into is the return hose going to a fitting on the cold side tank of the radiator which is where the pump intake hose originates from whether this is a cross flow or down flow radiator. Another configuration you might see is a tee in the inlet hose to the pump. Here I’m talking the classic Chevy pump whether a short or long pump and whether it is of clockwise rotation typical of 1955 thru 1986 using V-belts or the counter clockwise rotation of 1987 thru 1995 using the factory serpentine belts. Note that there are aftermarket serpentine belt systems that use the clockwise turning pumps. Also, note the fan needs to match the direction of pump rotation if you are using a pump driven fan.
These pre-1996 engines use or have a small bypass hole under the right side (passenger side) mounting boss to the engine. This is cored up to the right side head using about a quarter inch hole. There are those that feel this bypass is sufficient without the external hose bypass, I’m not a supporter of this idea, it’s a pretty small hole compared to the hose diameters.
The 1996 L30, 305 and L31, 350 Vortecs use a different pump, though related to the 87-95 pump it has different ancillary passages that use the bypass coolant for other functions that earlier models do not, so unless you are using a full up L30 or L31 Vortec with its factory fuel injection these are not a pump you want for an earlier engine or a Vortec not using the factory EFI. Also, these things never being easy the 1996 block casting may or may not have the traditional internally cored bypass and for sure the 97 and up blocks it is gone. Now you can use these 96-2002 production and the Vortec crate block with the older pumps but if the internal passage is not there then you need to put a plug into the pump passage, a screw plug being the best answer.
This I know is big data dump, make a copy and put it in a book, if you start playing across the years of these engines, this info will make life a lot simpler. And this is just cooling system data; there’s crankshafts, seals, flat tapes or factory roller cam differences, carburetors to EFI and different types of EFI that drive a lot of other changes.
Bogie
It should be noted that 87 (TBI) did not have a serpentine setup. It used a small 5 rib on the crank, water pump, alt. It used V belt(s) for the power steering and A/C if equipped.
88 is the first year of the GM V8 serpentine with automatic tensioner.
Below is what the pulleys look like.
www.bbkperformance.com
88 is the first year of the GM V8 serpentine with automatic tensioner.
Below is what the pulleys look like.
GM 5.0/5.7 F-Body/GM Truck 3 Pc Underdrive Pulley Kit (85-87)
Free SHipping on GM 5.0/5.7 F-Body/GM Truck 3 Pc Underdrive Pulley Kit (85-87). Order Now and Save!
www.bbkperformance.com
Does your radiator have a heater hose fitting near the top on the passenger side? My stock ‘75 SBC cooling has a hose from the Edelbrock intake to the heater core and another hose from the core to that fitting on the radiator. It flows regardless of thermostat being open. It seems you could just run a hose from the intake over to the radiator and and bypass the heater core.
Bruce
Bruce
I have a dart shp block small chevy build and it does not have the bypass hole made into the block and its like the 96 and up vortec that like Bogie said the hole is not there. I have a hose going from my water pump to my heater core then a hose going from my heater and drill a bypass hole in my thermostat and that is basically how mine is setup.
I don't know if that is good enough or not but that is how I read that is one way a bypass is done when the block does not have that hole in the block. I myself have had no difference in that setup vs the older GM 350 that I had that included the hole in the block and I also still drilled the bypass hole in the thermostat. I actually have three holes drilled as my engine gets real hot in traffic in the summer time and I need all the extra flow I can get and going without the three holes it runs even hotter and I have no choice. S10's are hard to cool at idle with v8 swaps.
Bogie has the best info above for a bypass option list.
I don't know if that is good enough or not but that is how I read that is one way a bypass is done when the block does not have that hole in the block. I myself have had no difference in that setup vs the older GM 350 that I had that included the hole in the block and I also still drilled the bypass hole in the thermostat. I actually have three holes drilled as my engine gets real hot in traffic in the summer time and I need all the extra flow I can get and going without the three holes it runs even hotter and I have no choice. S10's are hard to cool at idle with v8 swaps.
Bogie has the best info above for a bypass option list.
You can see in this photo, I have a hex plug in the top of the water pump and another in the front of the intake manifold. Could these be connected as a bipass? The stainless tubing showing on the left also connects to the intake and is connected to my heater.
![Image]()
I might be wrong but I do believe that is how the 96 and up vortec is hooked up on a lot of street rods using that motor without a heater core and they have a special tube or something with the 3/4 on one side and 5/8 on the other end and you hook the water pump up to the front of the intake like you stated.
When I first got my 96 chevy s10 back in the day it already had a 5.7 vortec in it and it had the water pump with the whole factory setup and was not hooked to my heater box and they had the water pump hooked up to a pipe fitting going to the front of the intake manifold just like you said and it never gave me any problems with any issues and I kept it that way but did not have the engine in very long as a rod bearing was going out and I put a different build in it.
When I first got my 96 chevy s10 back in the day it already had a 5.7 vortec in it and it had the water pump with the whole factory setup and was not hooked to my heater box and they had the water pump hooked up to a pipe fitting going to the front of the intake manifold just like you said and it never gave me any problems with any issues and I kept it that way but did not have the engine in very long as a rod bearing was going out and I put a different build in it.
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