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Discussion Starter · #1 ·
The thermostat on my '13 was stuck open -- it would run at around 120-130F on a cool day and 150-160F on a hotter day. I did not have long life coolant on hand, so I had to come up with a way of saving the coolant. What I did is attach a hose to the radiator drain nipple and drained 1 gallon of coolant into a clean water jug.

When I removed the thermostat, only a few drops of coolant leaked out. Replaced the t-stat, and poured the gallon back in. Approximately, 3/4 of the gallon went in. I poured the rest into the overflow tank and it got sucked back in after a few heat/cool cycles.

The old t-stat looked normal -- however, when I ran water through it (reverse direction) it was leaking massively (full facet flow was going through "closed" t-stat without an issue). Looks like the problem was that the rubber gasket on the t-stat itself (not the housing) shrunk to the point that coolant could flow freely around the "closed" t-stat.
 

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Stant knows thermostats.

ABC's of THERMOSTATS

A thermostat fails “open” if the return spring breaks or debris prevents the thermostat valve from fully seating or closing; allowing a steady flow of coolant to the radiator, overcooling the engine
A thermostat will fail “closed” if the wax element has been damaged by overheating (from loss of coolant, a defective electric cooling fan or fan clutch) or corrosion
Side note: In theory, a thermostat shouldn't fail in a "closed" position, if all is working well and well maintained.

Your mode of failure was in an open position. Maybe do the hot water test to see if there is any movement or if it stays put, i.e. open.
How to Troubleshoot a Faulty Car Thermostat
 

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Discussion Starter · #4 ·
How many miles were on the vehicle/thermostat?
143K Also, I boiled the old assembly -- it opened and closed normally at expected temperatures. As I said, the only issue is the rubber ring on the plunger that shrunk. I noticed on MOPAR replacement t-stat, they redesigned the plunger as to eliminate the rubber ring -- now it seals against a ridge in plastic.
 

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Side note: In theory, a thermostat shouldn't fail in a "open" position, if all is working well and well maintained.
Guess you don't use Motorad "fail safe" thermostats. :)

Fail-Safe Thermostats
MotoRad Fail-Safe® Thermostats offer premium, patented technology for superior protection over any thermostat on the market. Only Fail-Safe® is designed to lock in the open position when overheating occurs due to a failing cooling system component. This allows maximum coolant flow, thus preventing expensive engine damage.
 
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Of the handful of thermos I've replaced over the years, they fail in a way that lets coolant pass by either freely or easier. Never had one clamp shut and close off flow.
 

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Of the handful of thermos I've replaced over the years, they fail in a way that lets coolant pass by either freely or easier. Never had one clamp shut and close off flow.
My radiator had a leak (top plastic) and the car ran a few ticks below middle on the temp gauge. I assumed the thermostat was failing or combination of a radiator leak. Just replaced both radiator and Mopar thermostat, filled with Mopar coolant and now it hangs the the middle or a tick above the middle. I’m assuming this is how it should be to run efficiently?
 

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Needle location as you’re describing is fine.

I’d check the real temp with an OBDII scanner that can measure live data.

My 2014 T&C runs between 190-200 at 60 mph.
 

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Needle location as you’re describing is fine.

I’d check the real temp with an OBDII scanner that can measure live data.

My 2014 T&C runs between 190-200 at 60 mph.
I placed extra coolant into the radiator a day after replacing the radiator and thermostat and now it runs I think just perfect and consistent—a small tick just under middle. I’m very pleased with the difference and anyone seeing your car run a little on the cooler side ought to consider changing your thermostat. OEM thermostat costed me $33 shipped from
Amazon. My van use to run about a few ticks below middle.
 
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