Radiator has 2 overflow outlets, why?
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Junior User
Joined: Dec 2009
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From: Colorado
Radiator has 2 overflow outlets, why?
My radiator has two overflow outlets.
The top one is the smaller of the two, and sits right below the radiator cap. I have this one hooked up to the overflow.
The lower one is larger, and sits on the tube between the cap and radiator. This one goes to nothing currently. The problem is when the radiator builds pressure it sprays coolant into the engine compartment. Does anyone know what this second overflow outlet is for? Can I cap it and call it good?
I haven't checked the Hanes yet...it is also 0 degrees outside right now so no picture unless it is absolutely necessary.
The top one is the smaller of the two, and sits right below the radiator cap. I have this one hooked up to the overflow.
The lower one is larger, and sits on the tube between the cap and radiator. This one goes to nothing currently. The problem is when the radiator builds pressure it sprays coolant into the engine compartment. Does anyone know what this second overflow outlet is for? Can I cap it and call it good?
I haven't checked the Hanes yet...it is also 0 degrees outside right now so no picture unless it is absolutely necessary.
Posting Guru
Joined: Nov 2009
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because one wasnt enough
lol 
no are u sure the one u have hooked up is actually a hole i had a radiator that had 2 prongs once and it looked like they was both over flows but one of them was just a well extrution that resembled an over flow pull ur line off and make sure it has a hole in it and if it dont... move ur line and if it does go get a T- and put the 2 together and run it to the reserve tank
lol no are u sure the one u have hooked up is actually a hole i had a radiator that had 2 prongs once and it looked like they was both over flows but one of them was just a well extrution that resembled an over flow pull ur line off and make sure it has a hole in it and if it dont... move ur line and if it does go get a T- and put the 2 together and run it to the reserve tank
Senior User
Joined: Nov 2007
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From: Los Angeles, CA
My brand new radiator also has two. The lower one is capped with a fitting and hose clamp. The upper one was hooked to my overflow by my mechanic. I have no idea about what the lower one is used for. This is a four row heavy duty radiator.
My old radiator only had one.
My old radiator only had one.
Posting Guru
Joined: Jul 2009
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From: Toledo, Ohio
There is a small piece of hose, or maybe one of those vacuum line plugs, and it has a hose clamp on it as someone above stated. I didnt do it personally, but I know its plugged.
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Junior User
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From: Colorado
Wait, I just re-read what you said. Got to think about this. I will try to get a picture up tomorrow.
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The upper opening is for the overflow tank.
The lower opening is used by the 300 engine. The 1990 version of this engine uses a T in the heater hose to return part of the flow to the radiator. I don't know about other years. In junkyards, I have seen this nipple plugged with a rubber cap and hose clamp.
I have a theory about why the 300 uses this set up. First, there doesn't appear to be a water pump bypass hose on this engine. I think this T back to the radiator, serves as a water pump bypass and allows some water to circulate even if the thermostat is closed.
The second possible use is to warm the tranny fluid. The e4od will not lock up the converter until it reaches some internal temperature. In really cold weather the warm coolant flowing around the radiator internal heat exchanger may speed up getting the tranny fluid up to temp.
Just a theory.
Frank
The lower opening is used by the 300 engine. The 1990 version of this engine uses a T in the heater hose to return part of the flow to the radiator. I don't know about other years. In junkyards, I have seen this nipple plugged with a rubber cap and hose clamp.
I have a theory about why the 300 uses this set up. First, there doesn't appear to be a water pump bypass hose on this engine. I think this T back to the radiator, serves as a water pump bypass and allows some water to circulate even if the thermostat is closed.
The second possible use is to warm the tranny fluid. The e4od will not lock up the converter until it reaches some internal temperature. In really cold weather the warm coolant flowing around the radiator internal heat exchanger may speed up getting the tranny fluid up to temp.
Just a theory.
Frank
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Joined: Jul 2009
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From: Toledo, Ohio
The upper opening is for the overflow tank.
The lower opening is used by the 300 engine. The 1990 version of this engine uses a T in the heater hose to return part of the flow to the radiator. I don't know about other years. In junkyards, I have seen this nipple plugged with a rubber cap and hose clamp.
I have a theory about why the 300 uses this set up. First, there doesn't appear to be a water pump bypass hose on this engine. I think this T back to the radiator, serves as a water pump bypass and allows some water to circulate even if the thermostat is closed.
The second possible use is to warm the tranny fluid. The e4od will not lock up the converter until it reaches some internal temperature. In really cold weather the warm coolant flowing around the radiator internal heat exchanger may speed up getting the tranny fluid up to temp.
Just a theory.
Frank
The lower opening is used by the 300 engine. The 1990 version of this engine uses a T in the heater hose to return part of the flow to the radiator. I don't know about other years. In junkyards, I have seen this nipple plugged with a rubber cap and hose clamp.
I have a theory about why the 300 uses this set up. First, there doesn't appear to be a water pump bypass hose on this engine. I think this T back to the radiator, serves as a water pump bypass and allows some water to circulate even if the thermostat is closed.
The second possible use is to warm the tranny fluid. The e4od will not lock up the converter until it reaches some internal temperature. In really cold weather the warm coolant flowing around the radiator internal heat exchanger may speed up getting the tranny fluid up to temp.
Just a theory.
Frank
Hotshot
Joined: Sep 2001
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I don't know why it is there, but it is not a 2nd overflow/expansion tank connection. It is below the radiator cap, so it will not work for that.
Mine has it as well. I have seen some trucks that have the TB lines connected to it.
Mine has it as well. I have seen some trucks that have the TB lines connected to it.
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Junior User
Joined: Dec 2009
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From: Colorado
Interesting stuff. This is definitely not something I have ever seen before. Based on what you are telling me I will have to make a trip to the parts yard and see what I can find for this. Even if it is just a rubber cap for it.
Thanks for the replies, having the 300 in my 90 I would like to get it hooked up properly if possible.
Thanks for the replies, having the 300 in my 90 I would like to get it hooked up properly if possible.
Fleet Mechanic
Joined: Mar 2005
Posts: 1,603
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From: St Louis
As far as I knew, it was for the throttle body heater hose return, which was intended to keep the throttle body from freezing up in colder climes. Carburated engines would have this return port plugged as it would not be needed. The return hose on my 351 has rubber ends that connect to a metal pipe that served as the back side clips to hold the radiator fan shroud to the radiator. It looks like it will rust away someday anyway so I doubt you will find many, if any, good ones for you to use from the boneyard.