Thermostat failed closed, happy I avoided disaster

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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.
 
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!
 
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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 :
thumbsup2.gif
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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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