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Coolant Flow Direction

This is a discussion on Coolant Flow Direction within the General Help forums, part of the LSx Technical Help Section category; On the Water Pump, which is the inlet and which is the outlet? I thought the inlet was where the ...

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    Coolant Flow Direction

    On the Water Pump, which is the inlet and which is the outlet? I thought the inlet was where the Thermostat is, but the Power Steering Cooler is on the opposite opening, and it would make sense that the cooler would be on the inlet side of the Water Pump, right?

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    Senior Member Redphoenix1998's Avatar
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    The cooler is on the outlet side of the water pump. The two smaller hoses are for the heater, right next to it is the inlet where the tstat is located, and the outlet is at the top where the cooler also connects inline

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    Quote Originally Posted by Redphoenix1998 View Post
    The cooler is on the outlet side of the water pump. The two smaller hoses are for the heater, right next to it is the inlet where the tstat is located, and the outlet is at the top where the cooler also connects inline
    Ok...but that doesn't make sense...why would the outlet of the Water Pump be the cool side?

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    Redphoenix is incorrect. the outlet is where the thermostat is. the inlet is above that. Think about it. the hot coolant opens the thermostat, allowing coolant to exit block and go into radiator. the thermostat is the exit door.

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    Senior Member Redphoenix1998's Avatar
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    actually the inlet is on the Tstat side. I just did some research and second guessed myself for a minute. But the Tstat is supposed to restrict flow of coolant to the block for proper warmup. Once the coolant comes to operational temp, the Tstat opens to allow the flow of coolant to the block for circulation. Also Meziere waterpumps don't come with a T stat housing and according to Meziere it is also know as the Tstat Inlet housing.

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    Listen, i'm only gonna explain this one more time. I don't care what you read about aftermarket waterpumps or anything like that. The thermostat is the OUTLET. Period. From the general himself on gm service info. "Cooling Cycle

    Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Some coolant will then be pumped from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

    Coolant is also pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

    The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

    Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in keeping the throttle body cool.

    From the cylinder heads, the coolant is then forced to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or it will flow through the thermostat and into the radiator where it is cooled and the coolant cycle is completed.

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    Senior Member Redphoenix1998's Avatar
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    I have no idea where you got that information but obviously you do not understand how cooling systems work. That page is absolutely incorrect. My information was cut and pasted from general motors service information. What in the hell do you think a thermostat does when cooled antifreeze passes by it? It CLOSES. So how would it cool the engine if it was closed? Magic? Three wishes? sheesh. If i gotta put a clear hose on one of my cars here and run a video of how it works, i will. Not trying to get into a pissin match with ya but damn. Your page is wrong. wrong, and wrong.

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    here's a quote from GM's Service Information for 2000 Pontiac Firebird 5.7 LS1.
    The pump inlet is connected by a hose to the bottom of the radiator.
    I believe thats the hose that is connected to the T-stat, correct?
    According to GMs Service Information that hose is also called the "Radiator Outlet Hose."
    The radiator outlet has to be the water pump inlet. Get it?
    Last edited by Cutlass; 11-18-2009 at 03:33 PM. Reason: added year make model

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    Quote Originally Posted by mtspro6 View Post
    I have no idea where you got that information but obviously you do not understand how cooling systems work. That page is absolutely incorrect. My information was cut and pasted from general motors service information. What in the hell do you think a thermostat does when cooled antifreeze passes by it? It CLOSES. So how would it cool the engine if it was closed? Magic? Three wishes? sheesh. If i gotta put a clear hose on one of my cars here and run a video of how it works, i will. Not trying to get into a pissin match with ya but damn. Your page is wrong. wrong, and wrong.
    Did you copy that info from??
    That describes the coolant flow on engine design prior to the LS.
    The lower hose is coolant out of the rad. The stat is in that line of flow.. The diagram posted by red P is correct.

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    Quote Originally Posted by mtspro6 View Post
    I have no idea where you got that information but obviously you do not understand how cooling systems work. That page is absolutely incorrect. My information was cut and pasted from general motors service information. What in the hell do you think a thermostat does when cooled antifreeze passes by it? It CLOSES. So how would it cool the engine if it was closed? Magic? Three wishes? sheesh. If i gotta put a clear hose on one of my cars here and run a video of how it works, i will. Not trying to get into a pissin match with ya but damn. Your page is wrong. wrong, and wrong.
    So, I know I'm dredging up something old, but seeing as there wasn't a clear resolution on this question, I wanted to set the record straight.

    The T-stat housing on a Gen III (LS-style) engine is the engine water inlet. Or if you prefer, water goes from the outlet side of the radiator to the T-stat housing on the water pump. Please see the attached image from my '02 Camaro factory service manual, book 2, page 6-824.




    This thread helped me out a lot guys, thanks!

    Lowephoto.tumblr.com

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    The Tstat housing the outlet.

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    On a SBC, the thermostat is located on the outlet. On an LS1, the thermostat is located on the water pump inlet. Thats why GM calls it the water pump inlet. This info is also located in a book called "GM LS-Series Engines: The Complete Swap Manual" on page 147. You can preview that page of the book on Google Books and read for yourself.
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    I guess after two years, I'm still wrong...oh well.

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    its all good

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    I'm with ls1camino on this. I believe GM made a mistake on the manual and everyone quoted that. Before the ls1 almost all lower hoses were the pump inlet. I believe gm is still calling it that even though it is actually the outlet.

    Someone needs to install clear tube with a ball on a string to verify the flow.

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    It is confusing as hell and certainly makes more sense if the tstat housing was the outlet. Someone should go disconnect the upper hose on their car or truck and start the engine to see which way the coolant goes....and video tape it. Trust me, the mess will be worth it to know the answer

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    The thermostat is located in an area between the engine and the radiator. The classic small-block Chevy V8 located the thermostat on the "outlet" side of the motor, in the intake manifold. When cold, the thermostat was closed, and this prevented flow of coolant to the radiator. When the engine warmed up, the thermostat opened and coolant was allowed to flow to the radiator and back to the engine. The newer third- and fourth-gen GM V8's locate the thermostat on the "inlet" side of the motor - specifically in the inlet housing of the water pump. With this design, when cold, coolant is pumped through the rad, but is prevented from returning to the engine until the temperature of the thermostat has been reached, at which point the thermostat opens and the cooled coolant returns to the engine.

    Similar to a rad cap, a thermostat contains a spring-loaded sealing mechanism - but instead of reacting to pressure, it reacts to heat. Most thermostats do this with what is called a "wax motor". The wax motor is a cylinder containing a wax pellet that acts directly on the thermostat piston. As the wax heats up, and expands, it forces the piston to open the seal and allow coolant to pass.

    The Gen III/IV inlet thermostat location is designed to eliminate the following conditions / problems:

    With the older outlet design, an air pocket could be created under the thermostat after the thermostat was installed following maintenance or service to the cooling system. Since the coolant was prevented from reaching the thermostat's wax motor, the thermostat didn't open and allow cooling to begin until the air pocket had gotten hot enough to cause it - which would happen much later than for coolant, and often too late to prevent overheating and component damage. This excessive heat would be bad for any engine, but can be especially damaging for aluminum components. Elimination of this air pocket is one of the reasons why old-school racers would drill a small bleed hole in the thermostat's flange.
    The second problem is thermal shock that may occur at the radiator when hot coolant is released by the thermostat when the ambient temperature is near freezing. This sudden release of very hot coolant to a very cold radiator could cause thermal stress cracking in the radiator.
    Because the old-style thermostats were located at the top of the engine where coolant temperatures are highest, and because any vapour or trapped air always seeks the highest point in a system and therefore could get trapped beneath the thermostat, this design can lead to unwanted thermal cycling as the area of the thermostat heats and cools causing the thermostat to repeatedly open and close. The newer inlet location design was designed to eliminate this potential thermal cycling problem.

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    Member moesplace's Avatar
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    Pirate4X4.com is where I got this from pirate4x4.com/tech/billavista/Cooling/

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    Hmmm...thats the best explanation I've seen yet. Good info there!

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