Coolant overflow bottle

[sammisox]

Probably a dumb question, but I’m still a bit of a newbie so bear with me. 😅
 

This is the current situation of coolant overflow bottle in my truck which was not my doing. Drove it today for 40mins straight and coolant obviously came out of the open nub next to the hose line. 
There was no overheating issue, just simply think it filled up and came out of the opening. 

 

Will taking this tank out and swapping it for a 2.5L overflow bottle solve this? Does it need a vent anywhere/somehow? 
 

 

 

[eaglescout526]

Yes, if you put the 2.5L one in, it should solve your spilling issue but I think it requires an open cooling system conversion. 

[PIKE]

Adding a Macs tank and a 2.5 expansion bottle will convert you to an open system.

 

https://macsradiatorshop.com/product/macs-1987-1990-jeep-cherokee-aluminum-coolant-tank/

[sammisox]

Okay, this little black tank is the only thing connected to the radiator. I think the person I got it from was going to or trying to convert it but didn’t get very far. The radiator that’s in it has a cap on top

[PIKE]

The 2.5 expansion bottle is all you should need then. I use the word expansion because they way they work. You will notice the connection is on the bottom. When your radiator fluid gets hot it goes into to the bottle at the bottom. Then when the engine cools down it gets sucked back into the radiator. It is not an over flow tank.

[gogmorgo]

I don’t think we know enough about this system yet to make recommendations on what does or doesn’t need done.

 

We have a radiator with a cap and a clearly unpressurized reservoir. That sounds an awful lot to me like an open conversion has already been done.

If the hose connected to this black tank is going to a fitting on the side of the radiator filler (where the cap is, take a picture if you’re unsure) and there’s no other coolant reservoir present, that’s exactly what’s going on here. An open conversion.

 

If my two above assumptions are correct, there’s three possible explanations as to why it would overflow. 
The first, and simplest, is that’s the normal function of an overfilled reservoir in an open cooling system. Heat makes coolant expand, expanding coolant leaves when the coolant level gets too high. Its pretty easy to overfill a system when there’s no recommended level on the reservoir, or any good way to check reservoir level. If it quits puking after a few warm ups after the last top up it’s probably fine. It should stop after a while at temperature once it’s had time to slosh and splash it’s way out. It’s also important to make sure there’re still coolant remaining in the reservoir once it’s cooled back down. If there isn’t, it means either the overflow reservoir isn’t big enough, or that there’s some other leak somewhere. If you can, it would be good to try to mark this maximum level when cold for future reference.

The second possible explanation for puking is your gauges weren’t accurate and your engine was in fact overheating. It’s pretty unlikely. Easy enough to confirm with some other thermometer if it starts puking again, but usually if it’s getting hot enough to boil coolant out then it’s usually obvious what’s going on. Boiled coolant pushed out under pressure, not just a gentle overflow. I wouldn’t necessarily suspect overheating, but if an open conversion was done, it may have happened in response to an overheating issue that it didn’t solve. 

 

Third reason is something tangentially related to the cooling system has failed and is filling it with something other than coolant. I wouldn’t suspect that yet without more evidence of something seriously untoward going on like fluid cross-contamination.

[sammisox]

This is what it currently looks like. Yes, this black reservoir tank is connected right at the radiator cap. 
After I have been driving a bit (20+ mins) is when it seems to start coming out of the top opening next to the hose. Then once I am parked and turn the truck off it spits out a big puddle. However, the reservoir keeps getting filled because it comes out of the radiator, but never back into it so I’ve have to re-fill the radiator because it just spills out. 
 

This morning when I had to get it back home after sitting at a friend’s house all night, the black reservoir was completely full and then the radiator took 1/3 of a gallon of distilled water to fill it back up cause that’s what I had on hand

 

 

[olddude]

[cruiser54]

Looks to me like the PO tried to go "ricky racer" with the black tank.

A generic overflow tank with the stock radiator should work fine. The root cause could be as simple as a bad radiator cap.

 

No need to go with the Mac's conversion on a 2.5 engine. 

[jdog]

11 hours ago, sammisox said:

This is what it currently looks like. Yes, this black reservoir tank is connected right at the radiator cap. 
After I have been driving a bit (20+ mins) is when it seems to start coming out of the top opening next to the hose. Then once I am parked and turn the truck off it spits out a big puddle. However, the reservoir keeps getting filled because it comes out of the radiator, but never back into it so I’ve have to re-fill the radiator because it just spills out. 
 

This morning when I had to get it back home after sitting at a friend’s house all night, the black reservoir was completely full and then the radiator took 1/3 of a gallon of distilled water to fill it back up cause that’s what I had on hand

 

 

Is there a plug under the spot where the hose connects on that black tank? It can overflow into that but unable to return it with the hose on the top. If not get a different tank

[sammisox]

There aren’t any other plugs on it. I was going to just get a closed tank like the oem one or the 2.5L reservoir (something with a hose at the bottom) so that the coolant could flow back into the radiator…I was assuming that the coolant couldn’t get back into the radiator because the hose is at the very top of this tank

[gogmorgo]

You might be on to something there. It looks like there’s a couple plugged fittings on the front of the reservoir that might be helpful? Opposite the current hose. The picture’s not entirely clear. I will say it doesn’t look like a particularly big reservoir either, and it might also be nice to have a good way to see reservoir level without pulling the cap. 

Something else that will happen, if there’s a coolant leak in the pressurized side, it will suck air back in via the leak instead of coolant getting pulled back in. Air is thinner than water so it’s possible to pull air in somewhere that isn’t losing much coolant. But we can worry about that possibility after addressing the overflow from the rad not being below the coolant level in the reservoir. I guess I sorta assumed there was some kind of pickup tube or something in there. 

[pizzaman09]

Is it possible that the little black tank is under the top height of the raildiator?  Could you simply be fighting gravity?

[gogmorgo]

Also possible. If the pressurized side of the system is properly sealed off that shouldn’t be an issue, vacuum would keep the coolant in the radiator so long as air wasn’t getting in.

But it’s definitely worth considering when replacing the reservoir.