Heating Up 3/4 way, but not Overheating on Hot Days


Good day all:

I have a 2010 Rubicon that itself has 87K on it, but the motor got replaced at 15K under warranty, but wasn’t related to any cooling issue.

Moved to Arizona last year, and when it gets hot outside (105+), Air Conditioning running, and especially on the freeway (about 3K @ 80MPH), the temp gauge will make its way over to the 3/4 mark. It won’t make it any further than that, but runs up in that area every day. It’s usually after the first 5 minutes or so on the freeway, and stays that area until I get off the freeway about 15 minutes later. Then when I’m on the streets, it runs closer down the the normal straight up and down 1/2 way mark. When it runs at the 3/4 mark when I park it in the driveway, the overflow bottle is boiling, running out the whole, and the host from the radiator to the bottle is hissing pretty good.

I took it to a shop to diagnose, and they couldn’t get it to run up that hot (of course – it’s in the shop). They said they drove it a few blocks, and then pretty much let it idle in the lot for about 30 minutes, and it never got up that hi. They did see that the cooling fan switch and what not had some corrosion on it, wires starting to get bare, etc., so that whole assembly was just replaced. They also stated the radiator cap was only holding about 4 1/2 psi before failing, so that was replaced as well.

They did a block test and said there is nothing wrong with the motor itself. All pressures came back good, there’s nothing going on with the head gaskets or anything. They said the radiator looks in good condition visually, and there is no leakage from the water pump at all.

Yesterday, when it was boiling over, I dipped my finger in the fluid and tasted it to make sure it wasn’t just water, which trust me – after that taste, it’s not. lol

Could it possibly be a bad thermostat? I have always encountered in other vehicles when the thermo goes bad, it doesn’t have a “sweet spot”, it either fails, or it doesn’t.

I just don’t want to flush the system then it be the thermo. Or replace the thermo and all that it needed was a flush. Or do both of those and it’s something else, etc.

Anyone ever encountered anything like this in their Jeep? When I was living in WA state, it never did any of this. Granted, it’s 30+ degrees cooler, and up until just the last maybe month or so, it has always ran straight up and down on the gauge.

When I was pulling the 6×12 U-Haul trailer and encountered the Nevada desert via way of Idaho, is when I really started noticing it. It would get to that 3/4 mark, I could turn the A/C off, the heat on, she would cool back down to 1/2 way, then I could run the A/C again for about 5 minutes or so before she would get back up to the 3/4 mark.

I am just confused and at a loss! Hopefully someone has encountered this before, or is an expert in the Cooling field, and can steer me in the right direction!

Thanks in advance!

Salty Soul Jeep Shirt

Article source: http://www.wranglerforum.com/f202/heating-up-3-4-way-but-not-overheating-on-hot-days-2078785.html