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Radiator has 2 overflow outlets, why?

 
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Old 12-09-2009, 06:46 PM
little dutch
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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.
 
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Old 12-09-2009, 07:01 PM
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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
 
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Old 12-09-2009, 07:44 PM
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I have my second one blocked off.
 
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Old 12-09-2009, 07:49 PM
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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.
 
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Old 12-09-2009, 07:51 PM
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Pretty sure they both have holes, but will double check it.

Volvo, what did you work out to block the second one?
 
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Old 12-09-2009, 08:02 PM
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The second one (lower) goes to the intake as a preheater of sorts.. The line for it is below where the big hose(s) come from the air cleaner.
 
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Old 12-09-2009, 08:04 PM
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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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Old 12-09-2009, 08:17 PM
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Originally Posted by White 97 xlt View Post
The second one (lower) goes to the intake as a preheater of sorts.. The line for it is below where the big hose(s) come from the air cleaner.
Now that is interesting, my thermostat housing has a plug in it that might be for that.

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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Old 12-09-2009, 08:22 PM
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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
 
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Old 12-09-2009, 08:24 PM
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Originally Posted by fmr9 View Post
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
I have a 300 and mine is blocked off. I have a C6 so the tranny thing would not pertain to me either.
 
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Old 12-09-2009, 08:28 PM
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On my truck it goes to the throttle body and then from their to the intake... (probly for models that have the heated throttle body)
 
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Old 12-10-2009, 11:03 AM
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My 91 F250 with a 351W and E4od has the lower one going to the upper intake. My 89 has a T in the heater hose going to the same place.
 
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Old 12-10-2009, 11:41 AM
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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.
 
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Old 12-10-2009, 12:20 PM
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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.
 
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Old 12-10-2009, 09:37 PM
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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.
 

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