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#4759716 - 05/17/18 10:35 AM Thermostat failed closed, happy I avoided disaster
mrsilv04 Offline


Registered: 12/08/06
Posts: 8326
Loc: Illinois
Monday night, I had the thermostat on my 2000 Sierra 5.3 fail in the *closed* position. I had been driving for about a half an hour, with the A/C on, and I got a whiff of something that didn't smell quite right. I shut off the A/C and rolled down the window, and smelled more of what didn't smell right.

I took a look at the temperature gauge, and it was at 230... and rising quickly. I pulled into a parking lot, nosed it into the wind (it was a very windy out), shut it down, and put the hood up. There was nothing leaking, and it was full of coolant.

Once it had cooled down, I drove it the 6 blocks to a friend's house and left it in his driveway. Barely made it there, before it the temperature gauge was heading past 210, yet again.

Assumed one of three things.... thermostat, water pump, or a fan clutch. When it was hot, the top radiator hose was tight... and had noted that the fan appeared to be working properly. Start easy first, as always... so that meant the thermostat. I found that the thermostat had failed shut.

Factory thermostat, 18 years old with 130,000 miles. Came close to costing me an engine.

I'm going to place an order with RockAuto, and make plans to slap a new water pump, belts, hoses, plugs, wires, coolant, oil and filter on it as well, sometime in the next few weeks. Seems like it would be an excellent Memorial Day weekend project.

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#4759723 - 05/17/18 10:39 AM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
maxdustington Offline


Registered: 01/21/17
Posts: 1014
Loc: Toronna
I thought they were supposed to fail in the open position? Or is that just aftermarket tstats?

Planned obsolescence.

EDIT: A belated birthday gift! HBD!


Edited by maxdustington (05/17/18 10:39 AM)
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#4759774 - 05/17/18 11:27 AM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
Olas Offline


Registered: 12/11/13
Posts: 3969
Loc: Manchester, England
230f is only 110c and the pressurised system doesn't boil until 120c so it's more than likely going to be fine.
Good job you let it cool down when you did : thumbsup
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#4759787 - 05/17/18 11:43 AM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
EdwardC Offline


Registered: 11/14/13
Posts: 1900
Loc: Chicago, IL
Nice work! I had two overheating issues in the past, one due to a connector coming loose for the radiator fan and another where there was a leak in the cooling system. I caught both in time that both vehicles have kept going for many thousands of miles since.

Another trick that you probably already know, is to turn the air to full heat. It should help cool the coolant since I believe it's plumb in a loop before the thermostat.

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#4759908 - 05/17/18 01:33 PM Re: Thermostat failed closed, happy I avoided disaster [Re: maxdustington]
Chris142 Offline


Registered: 06/05/03
Posts: 17106
Loc: Deplorable in apple valley, ca
Originally Posted By: maxdustington
I thought they were supposed to fail in the open position? Or is that just aftermarket tstats?

Planned obsolescence.

EDIT: A belated birthday gift! HBD!
it's a myth. A stat can stick in any position. There are some garbage aftermarket ones that will latch open around 220f.
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#4759955 - 05/17/18 02:17 PM Re: Thermostat failed closed, happy I avoided disaster [Re: Chris142]
mrsilv04 Offline


Registered: 12/08/06
Posts: 8326
Loc: Illinois
Originally Posted By: Chris142
it's a myth. A stat can stick in any position. There are some garbage aftermarket ones that will latch open around 220f.


I would have *much* rather had a garbage one that stuck open. One that sticks open doesn't try to ruin your engine and leave you stranded.
_________________________
2004 Silverado - on its 3rd Jasper engine in less than one year.

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#4759958 - 05/17/18 02:18 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
ARB1977 Offline


Registered: 06/12/05
Posts: 5212
Loc: North Texas
If the factory one lasted that long. I would buy another. Good job on shutting it down in time.
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2018 CRV 1.5L (as of 05/11/18)
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#4759962 - 05/17/18 02:24 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
Claud Offline


Registered: 02/11/14
Posts: 593
Loc: Margate England
Why do you feel you need to replace the water pump?. Any signs of it leaking?.
I guess the other items are planned maintenance, I hope it's not because you had a wake up call on Monday night.

Claud.

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#4759981 - 05/17/18 02:38 PM Re: Thermostat failed closed, happy I avoided disaster [Re: Claud]
mrsilv04 Offline


Registered: 12/08/06
Posts: 8326
Loc: Illinois
Originally Posted By: Claud
Why do you feel you need to replace the water pump?. Any signs of it leaking?.
I guess the other items are planned maintenance, I hope it's not because you had a wake up call on Monday night.

Claud.


Just because it upset me badly enough. They're not that expensive, and I'm simply in the mood at this point. I can get a lifetime warranty unit for less than $60. I was assuming that I might need to replace it, and am still considering it.

This truck is used like a truck should be used (towing and hauling), and the peace of mind is simply worth it.
_________________________
2004 Silverado - on its 3rd Jasper engine in less than one year.

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#4760021 - 05/17/18 03:01 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
Nick1994 Offline


Registered: 02/19/13
Posts: 10442
Loc: Phoenix, AZ
My mom had an 03' Buick Rendezvous that the factory thermostat stuck closed while she was in traffic. It overheated and blew the head gasket. No coolant in the oil, but exhaust gases in the coolant. It would overheat if she wasn't moving so she was careful. She drove it for another year.
_________________________
2015 Hyundai Sonata 2.4L 82k Mobil 1 AFE 0w30 & OEM
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1996 Jeep Cherokee 4.0L 146k Mobil 1 HM 10w40 & Fram Ultra

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#4760037 - 05/17/18 03:09 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
supton Offline


Registered: 11/09/08
Posts: 12304
Loc: NH
I don't like doing timing belts but there is something to being said about replacing WP, tstat and coolant all at the same time.

Glad you made out ok.
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2011 Toyota Camry, base, 2.5L/6MT, 163k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 144k, ours
1999 Toyota Camry LE, 2.2L/4AT, 185k, his

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#4760050 - 05/17/18 03:17 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
Chris142 Offline


Registered: 06/05/03
Posts: 17106
Loc: Deplorable in apple valley, ca
Originally Posted By: mrsilv04
Originally Posted By: Chris142
it's a myth. A stat can stick in any position. There are some garbage aftermarket ones that will latch open around 220f.


I would have *much* rather had a garbage one that stuck open. One that sticks open doesn't try to ruin your engine and leave you stranded.
you didn't understand. they stick open and latch @ normal temps. The latch has no effect on it sticking closed anywhere in it's travel. They can still stick closed. The 1st time the engine gets warmed up they latch and stick open. Usually the day after it was installed.
_________________________
02 Wrangler durablend 10w40
87 F250 traveler 15w40
04 Tahoe super-s 10w30
Z400 castrol T 10w40
Can am maveric edge 5w40
57 case tractor 15w40

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#4760189 - 05/17/18 05:50 PM Re: Thermostat failed closed, happy I avoided disaster [Re: mrsilv04]
jhellwig Offline


Registered: 07/01/13
Posts: 1595
Loc: Ottumwa, Iowa
Am I the only one that remembers when this used to occur regularly? It has been 15 years since I had one stick closed but it used to happen more often. It was great when they came out with these fail safe ones but everyone I have had has stuck open. Now I just get the regular ones.
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1995 Chevy K2500 Suburban lt 5.7
2014 Toyota Sienna
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