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Discussion Starter #1
Just checking my fluids before a trip and the coolant looked low-ish. I haven't sweated this stuff much yet since I got the Jeep new and it's only 2-3 years old. It's a 2011. The coolant reservoir just says "min" and "max". Is that hot or cold? The level is below min when cold, but if it were actually at max cold there'd really be little/no room for expansion, so I guess it must mean hot?
 

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Below is the direct quote from the 2013 owner's manual. The coolant level should be checked at normal operating temperature with the engine idling.

"The coolant bottle provides a quick visual method for
determining that the coolant level is adequate. With the
engine idling, and warm to normal operating temperature,
the level of the engine coolant (antifreeze) in the
bottle should be between the ranges indicated on the
bottle."
 

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More specifically the hotter the engine is the more coolant will be pushed into the recovery bottle. So on an engine at operating temperature the level will be close to max, on a cold engine the level will be lower, close to the cold mark.

If your engine overheats coolant may be pushed out of the bottle overflow and will need to be added when cool.

The radiator cap controls the pressure the coolant is allowed to be released into the bottle, as well as allows coolant to be pulled back into the radiator as it cools. A bad radiator cap can cause the coolant to overflow even when the engine is not overheating.


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Discussion Starter #4
Thanks. I understand the fundamentals, I'm just used to it saying "min cold" or whatever so you know what they are talking about with the calibration marks. I take it in this case that you don't have any indication until it's heated up, except popping the cap and looking to see if it's way low - which incidentally is how at least some radiators were supposed to work up into the 60's, before they had overflows. I learned this the hard way when I thought the coolant was low in my Scout...

For my Jeep the radiator was full, as well as the plumbing to the radiator, but it was below min when cold. It was still below min after a long drive on the interstate, so either coolant has disappeared in the last 3 years or the factory underfilled it. I never have any drips on the ground, but I'm going to look closer now for indications of a slow drip from (hopefully) a hose or cap.

Any parts stores carry the stupid specialty mopar coolant? I checked O'Reilly but they didn't have it. They had Dex-Cool and "Asian car" stuff. All the manufacturers claim their generic green stuff can mix with everything else, but I don't feel like risking it.
 

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In the case of the JK the coolant bottle is vented to the atmosphere so some evaporation will take place. After several years adding some coolant is normal.

Check for small leaks around the back of the intake. While common on the JK they usually go unnoticed since they are under the firewall. Best place to look is on the sides of the transmission for signs of dripping.

If your coolant level is under the lower mark when the engine is hot add to the full mark when hot. If the level does not change when hot or cold something is wrong. You never want the coolant bottle to go empty and allow air to enter the radiator, this is especially important in reverse flow systems like the LS since air can circulate and get trapped at the top of the heads; even with the steam vents at the top of the heads allowing air in will cause an air bubble and subsequent overheating.

The JK coolant bottle is simply a hopper for coolant, so as long as there is coolant in the bottle the radiator should be full. A bad radiator cap that does not hold pressure can cause to much coolant to purge into the recovery bottle and allow it to overflow. Radiator caps are only good for a few years especially in hot climates and should be replaced regularly. I test a lot of caps here in Vegas and more than half fail the pressure test. Do not run a cheap cap, run a Stant, OE or equivalent. Most early radiators were a downflow design and the upper tank provided an air gap similar to modern fuel tanks. Most modern radiators are crossflow design and are designed to remain full with no air in the system.

Just be glad you don't have that stupid closed loop cooling system the XJ's had with the pressurized bottle.

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Discussion Starter #6
If the level does not change when hot or cold something is wrong.
Like hugely wrong, right? That coolant volume has to go somewhere. If not into the bottle, then out a ruptured hose or something. I take it caps seldom fail closed?

Is it a feature of the newer coolant formulas that they expand less with temperature? I don't think I have a major problem, and, for that matter, the distance between the max line and the vent is not much. It's not consistent with what I'm familiar with on my old fashioned vehicles, or at least it doesn't seem that way.
 

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Discussion Starter #7
Anyone know why there is no listing anywhere for a radiator cap for a 2011 JK? I checked Amazon, Rock Auto, Chryslerpartsdirect (or something like that), Oreilly, all nothing. Do I seriously have to drive over to the dealer? The vehicle is 3 years old.

No antifreeze locally, but at least they have Zerex online.
 

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Anyone know why there is no listing anywhere for a radiator cap for a 2011 JK? I checked Amazon, Rock Auto, Chryslerpartsdirect (or something like that), Oreilly, all nothing. Do I seriously have to drive over to the dealer? The vehicle is 3 years old.

No antifreeze locally, but at least they have Zerex online.
http://www.jcwhitney.com/2008-2011-jeep-wrangler-jk/radiator-cap/p2019334d57149y2008-2011j1.jcwx

http://www.amazon.com/Radiator-Wrangler-Liberty-Compass-Patriot/dp/B00B1LRA00

http://www.quadratec.com/products/51200_0004.htm
 
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