Mr.T

That sounds like it's in the range of normal, especially if temperature was decreasing during the test. It's not a perfect test, a tiny leak can go undetected and a small decrease in pressure can be due to temperature, a tiny leak in the test equipment, or maybe even air dissolving into solution with the coolant. What looks quite good is the latter part of your test, only 1 psi drop per hour.

You could check it again, trying to minimize temperature changes and checking for leaks in the tester with soapy water -- or just keep a close watch on the coolant level each morning for the next few weeks.

Zxkn

UPDATE:

Engine is fine, guess I lucked out.

However, I’m now looking to order a 5th thermostat in an attempt to find one that works. I can’t find Mopar ones anywhere. They’ve apparently been on back order for over 8 months now.

1). original Mopar => cracked housing
2). Motorad => failed catastrophically after 3 days
3). Stant => didn’t even install, wouldn’t even budge in boiling water (note, motorad housing like many, but valve itself had a different manufacturing mark)
4). Mishimoto => 5 days till it stopped opening.
5) ???? Any suggestions on what to try next?

How is it this hard to make such a simple part correctly? WTF?

Seizer

What temperature range is it supposed to open? On previous vehicles I could buy different opening temperature range thermostats. Not sure on the JK.

What I am getting at is are you certain you are at the required temps when testing it on the stovetop?

David Rodenberg

I have this same issue. I wasn’t getting any heat out of the vents, so I asked a 4x4 shop to take a look. They changed the thermostat but didnt fix the problem. They said I need to take it to the dealer. I assessed it myself and discovered the actuator that opens and closes the flap that allows more or less hot air mixture into the cab was stuck. After unsticking it. The hot air worked fine.

However, I then notice my engine temperature would go up to 3/4 when going up an incline. I was going about 70. I slowed down and the temp started to come down. After I crested the incline the gauge went back to middle. It continued to do this consistently. No leaks, fluids were at the right level etc. I had the system flushed and a new thermostat (non OEM) put it at the same time. Apparently OEM thermostats have been on back order for quite some time. No one seems to have them in stock. I changed the water pump and while burping the system, I noticed that the large burping funnel started to fill up and as it got hotter, the fluid started splashing out of the funnel and making a mess. I also noticed that the bottom radiator house was barely warm. The top radiator house was hot.

I deduced that the thermostat was not opening up. I decided to take out the thermostat from the housing to attempt to see if the thermostat was the issue. It ran great and didnt overheat. I ended up buying 5 different thermostats from various places (Napa, AutoZone, Advanced Auto, and O”Reilly’s. I decided to test them on the stove in boiling water before putting any of them on. None of them opened up when I placed them in boiling hot water. Not a single one. I just ordered a 6th one that’s actually got an aluminum body. I will get it tomorrow and will test it out.



I have 5:13 gears, 37” Cooper ST’s, 3.5 inch lift. Black 2015 JKU, automatic.

Seizer

That’s insane. Five failures in a row! I’m not doubting either of you. The sheer random probability that both of you had seen this many bad thermostats has got to be around 1 in 100000.

Mr.T

Looks like you're in Colorado Springs CO which is a little over 6000 FT altitude. Water boils at ~201 F at 6000 FT, and the thermostat for the 3.6L opens at 203F per a quick check at RockAuto.

I think that explains why none of the thermostats tested opened, it's just a relatively hot thermostat and at high altitude water boils at a lower temperature.

Zxkn

I’m not sure if the number of failures is really just random odds, or if it speaks to the lack of quality control on these aftermarket units.

It’s supposed to open at 203F. Water boils at 212F when at sea level. I confirmed water temp of 210-211 with a thermometer.

This last unit I put in is from gates. It looked like a better engineered product. It did not come in a motorad housing. It was a gates branded housing. The spring had a proper seat at both ends to keep it centered where the others did not. The center hole had more clearance around the encased wax piston. I’m at 150miles on it so far. I have high hopes.

In retrospect, I suspect that the poor spring fitment might be why the mishimoto failed so quickly. It didn’t seem to fit that well in the motorad housing and spring seat.

Zxkn

David, you could try adding coolant to the water, it should raise up your boiling point to match your elevation(though you probably want to avoid breathing the vapor/steam). Or just dump a bunch of salt in it. Either way, cross check your water temp with a thermometer to make sure the altitude isn’t effecting your test.

David Rodenberg

That is a very good point Mr. T. Looks like the boiling point here in Colorado Springs in the low 200’s, so maybe I’m not getting it quite enough to the point to where they should be opening up. Damn, I should have thought of that. I am pretty sure the latest one that I had in the jeep was not working, but maybe one or more of these other 5 (now 6) was actually working. I received another today in the mail. It as an aluminum housing. It actually seem like the best one yet. The spring seems to sit better and the thermo is more centered to the center of the opening in the thermo bracket. And its not a Dorman like all of the other ones were (as Zxkn stated).

Well, not sure how to test them at this point? Id rather test it to make sure it’s opening up before going through the whole process of installing it, losing antifreeze and making a mess. I wonder if putting a concentrated torch flame at the tip of the thermo??

David Rodenberg

Definitely will do that. As Mr. T pointed out, my boiling point here in the Springs is 10 or more degrees F less than at sea level. I am sure that the temp at my boiling point, is going to be in the low 200’s. Now the question is how do I test these? Torch flame??? Not sure if I want to risk boiling water with the coolant in it if I can avoid that: the vapor, using a pot that I should probably not use for cooking again etc…..

I’ll figure something out and repost. Glad your situation seems to be fixed Zxkn!!