GeneralDisorder Posted September 5, 2006 Share Posted September 5, 2006 This is more a theory question, but I've noticed that I have an extremely high thermostat failure rate - most especially when they have sat unused for a period of time. Example: I got a 93 Loyale and drove it home about two weeks ago. Running temp was perfect - about 1/4 on the guage, and it ran beutiful all the way home some 20 miles. Now mind you this engine had NOT run for over a year. Early last week I pulled the engine - drained the coolant of course and the thermostat was exposed to the air. It was without coolant for approximately one week and some change. I just filled it up and started it in it's new home tonight and it promptly overheated. I pulled the thermostat, as well as another I had in the garage and yet another from my running (but not currently driving) lifted wagon and set to work boiling them all on the stove. The control (from my wagon) opened perfectly and the other two remained stubbornly closed. I can open them a bit by hand so they are not stuck or anything..... what gives? Why when exposed to a little air for a short time after being succesfully used do they fail like that. The three I tested are composed of one OEM from the dealer, and two aftermarket ones. The OEM was one of the ones that didn't open, and I've had other OEM ones fail like that as well. But then this aftermarket one didn't fare much better so it seems to be common. GD Quote Link to comment Share on other sites More sharing options...
NorthWet Posted September 5, 2006 Share Posted September 5, 2006 This is more a theory question, but I've noticed that I have an extremely high thermostat failure rate - most especially when they have sat unused for a period of time... Over the decades I have been frustrated by what seemed a high failure rate with t-stats. Mine seem to be related somewhat to disuse, but more so to my being really bad about using just plain water as a coolant. If I were to guess, I would say that the design of t-stats really relies upon the coolant having the lubricants and anti-corrosives in "antifreezes". Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted September 5, 2006 Author Share Posted September 5, 2006 On a whim (and since they were still sitting on the stove) when I came inside I decided to boil the two failed units again. After getting to a rolling boil (so about 100 celcius) each of them opened about 1/8". Now they are both 88 celcius units, so I consider this a fail. The working unit opened completely before I even got the pot to a rolling boil. They are not frozen from lack of lube or anything like that - their temp has gone way up. What's inside one of these things? I think I'm going to die-grind one open and seen the innards.... GD Quote Link to comment Share on other sites More sharing options...
desertsubaru Posted September 5, 2006 Share Posted September 5, 2006 Try one from napa. They claim when they fail they will fail open. Just put one in my wagon so will let you know how it does. Quote Link to comment Share on other sites More sharing options...
Roundeye Posted September 5, 2006 Share Posted September 5, 2006 Try one from napa. They claim when they fail they will fail open. Just put one in my wagon so will let you know how it does. Times two. I have not heard of the fail open thing, but I have been using NAPA Superstats (ones for Oldsmobile diesel 350) (forget P/N) on all of my older Subes. No failures. GD: You're on to a wierd one there! My only guess would be something corrosion-related. I would see see how many pounds of force is required to open them and compare to a new (control) one of the same manufacturer. Use a push-pull gage, or a fish scale would even give you an idea of what it takes. If the force required is the same, then it could only mean the temper of the bimetalic spring has changed. If the force is more on the failed one, then it could be physical interferance in moving parts or again, sping failure. I hate problems like that. Something so simple that seemingly defies logic. Quote Link to comment Share on other sites More sharing options...
86subaru Posted September 5, 2006 Share Posted September 5, 2006 my napa went bad after 2 months , i used oem which i had Quote Link to comment Share on other sites More sharing options...
Roundeye Posted September 5, 2006 Share Posted September 5, 2006 my napa went bad after 2 months , i used oem which i had Was it a Superstat? There is a difference. Used 'em in my last 4 Subes, one has been in around 60K and 5 years. Quote Link to comment Share on other sites More sharing options...
bgd73 Posted September 5, 2006 Share Posted September 5, 2006 I ended up with a "stant" brand from advance auto, I went with it due to my remembrance of that name for years and nothing unusually failed on them. The Lubricant in anitfreeze no doubt feeds the longevity, regardless of brand. That little gadget I am sure has a very high quality control before shipping out from thier plants of manufacture- to have a problem once in engine would take some realistic deciphering. My only fail was the "miracle goop" that some folks/ oem used to keep system sealed. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted September 5, 2006 Author Share Posted September 5, 2006 Try one from napa. They claim when they fail they will fail open. Just put one in my wagon so will let you know how it does. That's known as a "locking thermostat". They lock in the open position when they overheat. Not really cool IMO, because then you are forced to replace the thing when you have a little cooling system problem. It is unfortunately impossible for any thermostat to fail open when it's cold. If the unit will not open in the first place, it cannot fail "open". GD Quote Link to comment Share on other sites More sharing options...
Snowman Posted September 6, 2006 Share Posted September 6, 2006 That's really bizarre about that one suddenly going bad. I haven't a clue why that would happen, but I suppose that the plain-water thing may have something to do with it. Unless I'm in a pinch, I always put in an OEM thermostat, and I've never had trouble with those. I got one from CarQuest that didn't work when it was new! Quote Link to comment Share on other sites More sharing options...
DaveT Posted September 6, 2006 Share Posted September 6, 2006 I ended up with a "stant" brand I have had good luck with the Stant brand also. The one I have in one of my cars seems to keep the temperature regulated better than others I've tried. Never had much trouble with the originals either. I have run straight water in an engine - leaked too much to waste antifreeze on - while waiting to rebuild. I saw no ill effects. Quote Link to comment Share on other sites More sharing options...
DasWaff Posted September 7, 2006 Share Posted September 7, 2006 On a whim (and since they were still sitting on the stove) when I came inside I decided to boil the two failed units again. After getting to a rolling boil (so about 100 celcius) each of them opened about 1/8". Now they are both 88 celcius units, so I consider this a fail. Perhaps when those units are in place, the pressure of the system helps force them open enough that they go unnoticed? Maybe this is why the Stant brand keeps a more stable temp? A 'working' themostat which was still restricting coolant flow would manifest as a greater variation in water temp. I have a spare that I think I'll boil now that I'm curious. DW Quote Link to comment Share on other sites More sharing options...
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