Overheating on 2015 JKU

Everything @BLACKJKU has mentioned is spot on . Just went threw this with my 2008 Sahara .
It went on for awhile . When engine pushed on the hwy it would start to fill up reservoir.
Once enough fluid has been pushed into reservoir it starts to over heat .
My Jeep was fine in the city .
It was hwy driving that pushed it over the edge .
A leak in the head gasket allows exhaust gases to push coolant threw the system which end up in the reservoir .

As funny as it sounds . I would check my reservoir every couple days and pump out reservoir with Turkey Baster to put coolant back into rad.
If on the hwy which I tried to limit would always keep on eye on it . Pump out if necessary .
The reservoir filling is a classic head gasket failure happening . For sure get a test kit to verify .
Since I got head gaskets done , heads machined flat it’s been perfect . Yesterday 3 hours hwy driving , 6 hours on a summit trail in 30 degree C weather .

Reservoir fluid rose by maybe 1/4” - 1/2” at the most which is normal as water expands when heated . When engine cooled that extra 1/2” was automatically sucked back into rad .

The fan cane on a few times but never full blast . Low speed only. Temp gauge straight up or to left of centre when on hwy .

Fel Pro makes really good gaskets sets and head bolts for the Jeep .

Well mmmmmm.
You’ve replaced thermostat
& pump .
You can smell coolant .
Coolant test negative .
You mentioned possible leaking rad ?
@BLACKJKU suggesting locking Torque Converter possibly heating things up.

Man this is a tough one . Part of me still thinking head gasket issue even though test negative .

May want to consider bringing it in for diagnoses and also have rad checked .

As anything going forward probably won’t be cheap .

Look at the lower driver’s side of your radiator. Look for a pink stain. That seam is a common area for a leak.

Pepperbelly said:

Look at the lower driver’s side of your radiator. Look for a pink stain. That seam is a common area for a leak.

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On my third radiator and this has been the area where it leaked on the other two.

Cimmerian said:

On my third radiator and this has been the area where it leaked on the other two.

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Everybody says to go with an OEM Mopar radiator but I wonder if an aluminum radiator might be better.

Pepperbelly said:

Everybody says to go with an OEM Mopar radiator but I wonder if an aluminum radiator might be better.

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Nope, everyone I have seen go that route have regretted it. The plastic flexes better than aluminum. Only good thing about the aluminum is you can theoretically repair it when it breaks. It has to do with the actual design of the JK moreso than the radiators. Too much frame flex on them.

As far as aluminum goes though, if you're deadset on it I heard the CSR ones are the best but they're like $600 a pop. My junkyard Mopar was $50.

Let's not forget how many times we've heard of people changing multiple thermostats before finally getting one that functions as it should.

If you have JScan, set up your phone so you can see it while you've got the hood up. Cold start your JKU and wrap your hand around the upper hose and check the coolant temp on JScan when you feel the coolant start to flow. This will let you know if the t-stat is opening when it's supposed to. If it opens well past where it should, the t-stat may be sticking.

Pepperbelly said:

Everybody says to go with an OEM Mopar radiator but I wonder if an aluminum radiator might be better.

Click to expand...

I went with an aluminum Cold Case rad about a year ish ago . Started leaking after 2nd off road trip.
@Cimmerian was bang on when he said they don’t flex as well . The aluminum with plastic tanks are more forgiving due to ORing sealing the the tank to rad . It allows some flex . The aluminum being all welded is to rigid for off road . Keeping the upper mounting bolts loose didnt help me at all.
Went with a Crown that works really well. Runs cooler than other rad’s I’ve had on before the Cold Case disaster .