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danielgolf1 D thanks #1 · Apr 14, 2003 thanks Sort by Oldest first Oldest first Newest first Most reactions #2 · Apr 14, 2003 Re: how do you know your thermostat is bad !!! (danielgolf1) guy at the shop says...dood, your thermostat is shot.

normally, your heat wont work very well..itd take a while for it to kick in, sometimes not at all...stuff like that. i dont know the other symptoms or what exactly to check to know for sure #3 · Apr 14, 2003 Re: how do you know your thermostat is bad !!! (danielgolf1) Engine temp will not come up at highway speeds, maybe only at red lights. IIRC these thermostats are fail safe in that when they fail they do so in the open position so the car does not overheat. It just won't want to warm up. [Modified by MikeBlaze, 7:56 PM 4-14-2003] #4 · Apr 14, 2003 Re: how do you know your thermostat is bad !!! (Severance) Do you know what the t-stat does? It opens when your coolant hits a certain temperature to let water flow through the radiator and cool down. It can fail in two ways: 1. Stuck open Your car will take a long time to heat up, and when you're driving at a good speed downhill on a cool day, your water temp gauge will start to go below the 1/2 way mark. 2. Stuck closed Your car will overheat. If your car is overheating and you want to know if a stuck t-stat is causing it, once the car is heated up touch the upper and lower rad. hoses. If one is a lot colder than the other, your t-stat is stuck closed. Hope that helped! ROB #5 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (rtmeikle) quote:[HR][/HR]Do you know what the t-stat does? It opens when your coolant hits a certain temperature to let water flow through the radiator and cool down. It can fail in two ways: 1. Stuck open Your car will take a long time to heat up, and when you're driving at a good speed downhill on a cool day, your water temp gauge will start to go below the 1/2 way mark. 2. Stuck closed Your car will overheat. If your car is overheating and you want to know if a stuck t-stat is causing it, once the car is heated up touch the upper and lower rad. hoses. If one is a lot colder than the other, your t-stat is stuck closed. Hope that helped! ROB[HR][/HR]Excellent explanation. http://****************.com/smile/emthup.gif It's a relatively simple replacement. If you're in doubt, just replace it. #6 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (MikeBlaze) quote:[HR][/HR]IIRC these thermostats are fail safe in that when they fail they do so in the open position so the car does not overheat. It just won't want to warm up. [HR][/HR]Correct. #7 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (Air_Cooled_Nut) quote:[HR][/HR]IIRC these thermostats are fail safe in that when they fail they do so in the open position so the car does not overheat. It just won't want to warm up. Correct.[HR][/HR]Incorrect. Maybe that's the design, but it doesn't always work. Tell that to my t-stat that stuck closed a few months ago!

ROB #8 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (rtmeikle) quote:[HR][/HR]IIRC these thermostats are fail safe in that when they fail they do so in the open position so the car does not overheat. It just won't want to warm up. Correct. Incorrect. Maybe that's the design, but it doesn't always work. Tell that to my t-stat that stuck closed a few months ago!

ROB[HR][/HR]Was it OEM? #9 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (MikeBlaze) quote:[HR][/HR]Was it OEM?[HR][/HR]Yep. I've heard the rumor that they're only supposed to fail open, but I've heard from a lot of people on the 'tex (besides me) who had them fail closed. Also, the Bentley mentions both, so maybe they fail open more often; but to say they never fail closed is just wrong. In fact, I've heard of SEVERAL people who've had them fail closed. ROB #13 · Jul 9, 2015 My thermostat failed in the closed position

rtmeikle said: quote:[HR][/HR]Was it OEM?[HR][/HR]Yep. I've heard the rumor that they're only supposed to fail open, but I've heard from a lot of people on the 'tex (besides me) who had them fail closed. Also, the Bentley mentions both, so maybe they fail open more often; but to say they never fail closed is just wrong. In fact, I've heard of SEVERAL people who've had them fail closed. ROB Click to expand...

I've been troubleshooting my 99 2.0L Beetle which has been overheating. Thought for sure it was the water pump, because no coolant was returning to the reservoir, even at high RPM. So I tore it all down and was ready to replace the water pump. Pulled the thermostat out and reached behind it. The water pump was not turning. I would expect it would turn and that I might find bits of broken impeller, but no. So I put the thermostat in boiling water. It didn't open. Then I realized water isn't going to get any hotter than 100 degrees C. So I put the thermostat in a pan of cooking oil, brought it up to 200 degrees C and it did NOT open. Guess I don't need a water pump, but I discovered my timing belt was worn pretty badly. So I'll put in all the new parts anyway. Looks like God spared me from a broken timing belt and bent valves. Live and learn.

0 Reply #10 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (rtmeikle) quote:[HR][/HR]but to say they never fail closed is just wrong. In fact, I've heard of SEVERAL people who've had them fail closed. ROB[HR][/HR]Never said they will only fail open, only that that is what they are designed to do. Anything can happen... Murphy's law is a *****!

[Modified by MikeBlaze, 4:29 PM 4-15-2003] #11 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (MikeBlaze) quote:[HR][/HR]Never said they will only fail open, only that that is what they are designed to do[HR][/HR]No argument there, I'm not sure what they were "designed" to do. I just want people reading this to know that they are not, as you said, "fail-safe" by ANY means! Sorry to get a little off topic, but my initial explanation should be enough for you to diagnose your t-stat whether it is stuck open or closed.

ROB #12 · Apr 15, 2003 Re: how do you know your thermostat is bad !!! (MikeBlaze) quote:[HR][/HR] IIRC these thermostats are fail safe in that when they fail they do so in the open position so the car does not overheat. It just won't want to warm up. [Modified by MikeBlaze, 7:56 PM 4-14-2003][HR][/HR]designed or not mine got stuck closed!

And a week later I saw a guy with 2.0 looking at his engine and a big puddle of coolant in front. He said it overheated, I checked the hoses from his radiator (one was hot the other was cold) and it was his t-stat, it got stuck closed as well. THEY ARE NOT FAIL SAFE!!!!! Also there are no symptoms when will it fail, it just does whenver it wants to.

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