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.

because one wasnt enough:-missingt lol :-X15 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:-roll

I have my second one blocked off.

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.

Pretty sure they both have holes, but will double check it.

Volvo, what did you work out to block the second one?

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.

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.

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.

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.

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)

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.

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.

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.

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.

Just an update on this if anyone is interested.

I got a small piece of hose (probably leftovers from the parts yard) and clamped it on the second, unused, overflow outlet. I just plugged the other end with a piece of brass I had lying around and put a clamp on it as well. Worked great, thanks for the information on it.

Raising this from the dead. My 1985 F150 4.9 I6 has this "second" port just below the radiator cap.

I discovered it because when I over filled my coolant, it came pouring out on the ground.

Does anyone know what to plug it with? Do you seal it with a gasket sealer or something?


What scares me is I've been driving it with the hole unplugged since I've owned it. :'(

My guess is some mechanic replaced the radiator and didn't realize there was another hole. That's what she said

Did you read the previous post to see what he did? Maybe there is a rubber cap in the “HELP” section at the parts store that will work. Every replacement radiator that have purchased came with a cap to block off that port if you didn’t use it in your application. Don’t forget to use a hose clamp. It is below the seal on the cap and is pressurized.

They sell a bypass cap assortment in the Help parts. That's what I used to plug mine.

https://cimg4.ibsrv.net/gimg/www.for...edcd50be3e.jpg
That’s where it goes now🤷‍♂️

I dont know why you revived this thread, but if you must know what its for, it T-s into the heater core line(not sure if it was inlet or outlet, I believe inlet...) and its purpose is to reduce gurgling noises and potentially help with flow. The noise I think was the primary. I dont think its really necessary, but thats what it does.
https://cimg0.ibsrv.net/gimg/www.for...bde62577c4.jpg
here is a 4.9 with the outlet, i think, to the heater core
https://cimg3.ibsrv.net/gimg/www.for...308f81363c.png

I always thought you use the top one with an overflow tank or the bottom one with an expansion tank.

that may be true somewhere but the function of expansion tank sometimes is the only thing on a vehicle, sometimes only overflow, sometimes both. depends on how its all setup. It is ostensibly just a place that allows coolant to return to the radiator the reason isnt really that huge. the top one is controlled by the cap spring/element which will expose or block the opening based on pressure

Not on v8's that bottom port connects with a pipe, going all the way back to your throttle body, to keep it from icing up in cold weather.
https://cimg5.ibsrv.net/gimg/www.for...318b544580.png
https://cimg5.ibsrv.net/gimg/www.for...1f9d6748a0.png

The lower connection allows air to be purged from the system. It's easier to purge than trying to get the system to push the air through the heater core and back down through the water pump. Notice it connects to the highest hose in the cooling system.

Damn
 

Sure is a lot of discussion for a dead topic, huh?

not at all, if you had read then you would have noticed that its a lot of discussion because it was in response to a recent inquiry.

now, it was not related to the OPs subject, however it was easy/simple enough that it didnt warrant making a thread about it since no one needed help