This is a general thermostat question for a non Ford truck product. My daily driver is a 99 Subaru outback. I flushed and drained the coolant using a chemical flush (Cool Prep). I used the chemical because my former mechanic more than likely used the garden hose flush and fill 5 years ago. The tstat stuck after the flush. No heat and the engine ran hotter than usual. I took it out and did the boiling water test and it opened. It was dirty. I reinstalled the Tstat,flushed the system and it works great.

Should I spend another $20 on a new Tstat? Is it common practice to replace tstats after a flush?

I am flushing my e150 next week and need the Subie for my parts runner. My Honda needs a flush too. We need at least one of the Ford vans and a sedan running at all times. Seems like all the PMs like oil and coolant changes happened this month on all 4 vehicles.

 

I can't imagine putting a used t-stat that has failed back in.

 

It failed because the chemical cleaner did it's job and cleaned a lot of crap out of the system that may have blocked something. There is a possibility that it was not a stuck thermostat. Something was blocking the coolant from flowing or I did not fill the system up enough. It's a Subaru and rarely needs any repairs. I change the oil and the brakes.

I put the T-stat back in to test to see if the thermostat actually failed. It worked in the pot of water. I used a candy thermometer inside the pot of water and the thermometer opened at about 180 degrees.

It takes 5 minutes to install the T-Stat and entire cooling system is 1.5 gallons. It's running great with reverse osmosis water. I plan on buying a new Tstat this week and filling it with coolant and distilled water.

I tested the cleaner on a small cooling system before I try it on my E150 van next week. I had the radiator of the E150 van replaced on the road in Montana and the installer filled the radiator with water from the bathroom sink. He mixed Ford Gold with the old garden variety green coolant. He only drained the system-did not flush it. I need to flush it ASAP as it's probably turning it into jello.

I have 2 gallons of Zerex green for older vehicles like my 1998 E150. My E150 van seems as durable as the Subaru.

 

The other reason to replace the thermostat is that it's 5 years old.

Sixto
93 E150 Chateau 5.8 191K miles

 

Then why do you ask if you should change it?
You already made up your mind and did not provide all the facts.