[Jeepman]

Y connectors only apply if you have rear heat. They are near the back, closer to the firewall. Horizontal one is very visible, and it hides the vertical one behind it. (on my 2016 DGC)

If your reservoir empties on cool down, coolant is being sucked back to the engine. A leak in the system, unless very small, would not normally allow that to happen. Air would be sucked in through the leak instead. That's why one can't trust only the reservoir to determine coolant level in the system.

What work has been done on the coolant system recently? What engine and normal operating range? 234 is within the operating range, I believe. 180F to 235F/240F possibly.

A previous Thread that relates:

2011 town & country

What can be done to make cooling run when temp is over 200?

www.chryslerminivan.net

Plan your analysis, fill it up and see what happens. Hose clamps in good shape? Sometimes they lose all strength.

 

[Jeepman]

I changed the thermostat in late August, the bleed was good afterwards and the temps have been pretty good since. It runs between ~205-221 most of the time, will drop to 190s on long descents and go to about 123 on ascents with the AC on. This time it just kept climbing, even with the fan operating, until I got moving again and jumped as soon as I stopped.

What would it mean if it gets sucked back into the engine on cool down? Bad head gasket?

Not necessarily, head gasket could be a small leak. Recent experience with that on a 2004 Acura TSX. Coolant is sucked back on cool down (radiator stays full). Can't find leak using pressure test. Shop says leak to engine. Less than a jug full of premixed has leaked out since January.
A hose, hose clamp or radiator seam leak may be sufficient size to allow air to be sucked back into the system. When engine is hot and just turned off, can you hear a hissing sound under the hood? Do you have a Mechanic's stethoscope to do some probing? Might work.

 

[Jeepman]

A pressure test will tell you two things about the leak:

• its location, maybe
• how the leak is responding to the pressure (watch the pressure drop)

 

[Jeepman]

What engine are we talking about? On my 2007 GC 3.8L, the lights and alarm went off when a lower radiator hose clamp (OE spring type) let go. Got some water in there eventually and nursed it home (about 7 minutes from where I stopped). Replaced the clamp after that.

No leaks for years after. Eventually 3 or 4 years later, the radiator sprang a leak and we replaced that.

For the Pentastar engine, I believe the normal range is up to around 230 although Jeep JK Owners are mentioning 240, even 245. The engine tends to like higher temperatures. Well, maybe not so much when it comes to the needle bearings in the rockers.

3.6 pentastar overheating

Hi, i am newbie in this forum. i have done my homework regarding 3.6l engine running hot. the problem i live in harsh environment which is 125f+ in the summer time and 45f to 60f in winter time. so let me tell you what i have done to fight the overheating on my 2014 JKU robicon Auto trans...

www.jkowners.com

230 is definitely not overheating for the 3.6L, even seeing 240 is pretty typical. A lot of us (including myself) don't really like seeing the numbers so high, but there's no choice but to accept that the engineers designed the engine to operate at this temperature range. When it's hot weather I try to monitor it and back off the throttle to keep it below 230 because I feel it might stand a chance of increasing engine longevity, but that's far from actually overheating for this engine.

Air in the system will present some weird temperature fluctuations though. Back in the days of the Bricklin.

TECH TIP: Overheating

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A bricklin with a 15 pound radiator cap will not boil the water in the radiator until the coolant reaches approximately 250 degrees temperature. With anti-freeze, the boiling point is 250 to 260 degrees. You can run your car at 240 or 250 degrees without hurting anything, as long as the water in the radiator doesn't boil. Once the water boils, it will immediately push water out the overflow, lower the coolant level in the radiator, and give you air bubbles circulating through the cooling system. Air bubbles do not cool an engine, so the engine temperature will immediately skyrocket. Your main concern should be to keep your engine below the boiling point of your coolant. If your radiator cap is no good, it will lower the boiling point of your coolant to 212 dgrees. A leak of any type anywhere in your cooling system will have the same effect. That is why you must have a good radiator cap on your car
Many people get worried if their car gets up to 220 degrees. On a hot day, going up a hill with your air conditioner on, that is a normal temperature, and is nothing to worry about, as long as you aren't losing coolant. You can safely operate to 240. Above 240 you are nearing the boiling point of your coolant, so start being concerned.

So, 234 was ........not so bad??

 

[Jeepman]

That's useful info. Thanx. Sorry, 2015 with the 3.6.

I replaced the thermostat about 2 months ago and it seems to have gone bad. I got everything dried off, refilled and bled sufficiently and as it warmed up over ~190° it started dripping from under the radiator cap so I let it go for a minute that way. When I shut it off the radiator level dropped immediately but the reservoir is now about an inch above the max level. I let it sit and cool down below 100° while I wiped it down again and restarted. Immediately it was dripping out of the thermostat, it looks like it has a small crack so it's getting replaced and we'll see where it goes after that.

My thinking is the stat can't do it's job because it's leaking there and letting it get hotter than usual and it's spewing out at the cap. Sound right? I will get a new cap too and maybe the 2 hoses also if the store that has the new thermostat has them. Is there anything else that would cause enough pressure to blow out at the cap that I should be concerned about?

Sounds like you are on the right track to me.

Air bubbles do not cool an engine, so the engine temperature will immediately skyrocket.

!6 psi isn't much. It's about equivalent to a 7 kg turkey perched on top of your radiator neck.