Radiator overflow tank cap ?

[WranglerMan]

First off I’m sure this is going to be a stupid question but I’m going to ask anyway.

In a quest to learn more about my Wrangler I popped the hood and just started checking things out and reading what is stamped on a lot of stuff, anyhow the radiator overflow tank cap has 21psi stamped on it so I took it off to just look at the plastic cap and now comes the question, when putting it back on it screws down and stops but if you turn it just a little harder it pops past the stop and goes another 1/2 turn more and bottoms out so when putting it back on what’s the correct position, turn just until it stops or turn past where it first stops and go until it bottoms out.

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[Rhinebeck01]

First off I’m sure this is going to be a stupid question but I’m going to ask anyway.

In a quest to learn more about my Wrangler I popped the hood and just started checking things out and reading what is stamped on a lot of stuff, anyhow the radiator overflow tank cap has 21psi stamped on it so I took it off to just look at the plastic cap and now comes the question, when putting it back on it screws down and stops but if you turn it just a little harder it pops past the stop and goes another 1/2 turn more and bottoms out so when putting it back on what’s the correct position, turn just until it stops or turn past where it first stops and go until it bottoms out.

Stop when it first stops. That extra bit would be an over tightening.

Also, no question is a stupid question..

I did verify this on my JL.

 

[WranglerMan]

Stop when it first stops. That extra bit would be an over tightening.

Also, no question is a stupid question..

I did verify this on my JL.

What does going the extra bit do,it almost seems like it two pieces. At first I was thinking that the inner part needs rooms to lift like a safety relief cap or does have that extra room allow it to just vent without leaking as the gasket has a seal.

 

[homerun]

Are you sure you are looking at the overflow tank, or the radiator cap itself? The overflow tank should just be a plastic snap as it is not under pressure, however the radiator cap is under pressure and should have psi rated spring that will open as the temperature increases which causes the coolant to expand, the exapanding coolant pushes out the spring and the excess is released to the overflow tank. There should be a rubber tube that sucks extra coolant back to the radiator system as the coolant cools down.

 

[WranglerMan]

I’m pretty sure this cap is not the radiator cap



And this is tank I am looking at

 

[homerun]

That indeed looks like to the coolant overflow reservoir cap. I am surprised it has a PSI rating on it. Don’t have a JL as I am impatiently waiting for the JT. So what I thought might be an easy question has me stumped. I would need a Chilton or Haynes to figure that out.

Here is some extra info on the radiator system that you might be interested in.

https://www.cruisingworld.com/understanding-coolant-recovery-bottles

 

[WranglerMan]

Here is a better pic/vid of the cap, like I said it screws down and then hits like an internal stop but if you twist it a little hard you can go past that and then it bottoms out, I am guessing as stated by @Rhinebeck01 your supposed to stop when you hit the first stop, I screwed it back down just until it hit the first stop and ran a 20 min errand and no leaks out of the top and the coolant temp was running 195-205 and the level in the tank while running and stopped was at the max mark so maybe it’s some type of pressurized system

 

[Rhinebeck01]

@WranglerMan

Was just over at a local Jeep dealership. As usual I was poking over some of the new JLU's there. Anyway, ALL 4 that I looked at, had that cap tightened to the first stop as my new JL's was. So, I'll assume that first stop is where you would leave it. Ahhhhh, until told otherwise by somebody that knows for sure... ho, ho, ho.

For the record, that is equivalent to a radiator cap it seems .......... daaaaaah, but the radiator itself does not have a radiator cap.. not like what most of us are familiar with, that we saw on say a 2007-2014 JK. The JL has the cap that @WranglerMan gave us a pic of, and it is marked 21psi as it is a system that is pressurized. So, new to me and I don't know nomenclature, etc.. Looks like you would remove this cap to add additional coolant if needed.

 

[WranglerMan]

@Rhinebeck01 thank you so very much for taking the time to not only check on this but report here, I was out in the garage a little while ago and had the hood up and was searching and searching for a radiator cap that I am used to seeing on the radiator that’s metal and not plastic and besides that the overflow tank that I along with lots of others are seeing is plastic like what I have but does not a cap that has a pressure rating on it.

In the past with other vehicles when I have needed to add just a little coolant I have used the overflow tank as this was an easy way to add just a little and it had the plastic snap cap that one could easily open and just pour in coolant and then when the vehicle cooled down it would draw it into the radiator with a vacuum and n the early days of those tanks there were no min/max line you just kept them about 1/2 full, I do believe the ones with markings came later but could be wrong.

It still amazes me how much things have changed from the old days with all the new technology especially have the radio as a brain that controls a lot of what a vehicle does, like a close friend told me it’s all grand when it all works but when it breaks you need an Electrical Engineering degree to fix it.

Thanks again for taking time, I am sure as I go along with my new Wrangler I will learn more and more everyday but it’s not as simple as the only days when you could pull your vehicle under a shady tree or into a garage and pretty much pull the while motor and rebuilt it with some fairly simple tools.

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