Thermostat? (1 Viewer)

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Aug 24, 2008
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12
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72
Location
Nashville TN
While driving the kids to school yesterday I noticed that my heater was not blowing hot air. I took a look at my temp gauge and it was in the red. Does this mean my thermostat has had it? Any ideas and thanks in advance.
 
You sound amazingly calm for someone who just ran their engine temp's into the red. You'll be very lucky if all you need at this point is a new t-stat. (Plus that's not likely the issue.)

So what did you do? Pull over immediately? Pop the hood and check the coolant level? Listen for gurgling/boiling noises? Check all belts and hoses? Look for leaks? Or...?
 
Pop the hood and check the coolant level. Listen for gurgling/boiling noises. Check all belts and hoses. Look for leaks.

Question Marks Removed...
 
He must be saying the temp slider on the AC control unit was in the red. Not sure, but I hope so.
 
While driving the kids to school yesterday I noticed that my heater was not blowing hot air. I took a look at my temp gauge and it was in the red. Does this mean my thermostat has had it? Any ideas and thanks in advance.

Yes. I'm 99% sure your thermostat failed. Get an OEM one - even if you have to wait a day or two for it to come in. The parts store thermostats are junk by comparison.

It is a relatively easy job - but gets more involved when you start looking at the WYIT (While you're in there) aspects of it. With the coolant out - its probably a good time to replace all the rubber coolant hoses. Since you're replacing hoses, may as well do belts, right?

Oh, and you wouldn't want to do all of this and leave any sediment or old coolant in the system - so a multiple flush is in order. Be sure to disconnect and flush both front and rear heater cores from the firewall - and get the soft lines up underneath.

Now that you have a pristine clean system, you wouldn't want to put just any coolant in so you'll want to $28/gallon Toyota special coolant - two gallons of it. Oh, and distilled water to mix with it.

But, yes, it sounds like your thermostat failed. I'm assuming the system was full of coolant before it failed - if not, it could be very bad. Changing just the thermostat isn't hard - but you will likely drop most of your coolant to do it. Be sure to orient the jiggle valve properly.

Were you boiling water and steam out of the radiator cap? If not, I wouldn't worry about it - if the engine is hot enough to do damage and had coolant in it, the radiator cap would be screaming like a kettle in a bonfire.

IMHO YMMV I'm not a mechanic.
 
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Yes. I'm 99% sure your thermostat failed.

Why are you so sure of that?

No in cabin heat is a symptom of severe overheating, regardless of the cause of the overheating. (For example: Blown headgasket, blown water pump, busted water pump belt, etc...).

I'm not saying it's NOT the t-stat, but there are plenty of variables to consider when dealing with acute overheating.
 
Changing just the thermostat isn't hard - but you will likely drop most of your coolant to do it. Be sure to orient the jiggle valve properly.

On a 91-92:

Very easy to get at the t-stat, without losing much coolant at all.

No jiggle valve issue as the t-stat does not sit "sideways" as on a 93-97.

There *is* an o-ring issue: Make sure you get the o-ring that sits on top of the t-stat, and install it carefully.
 
Why are you so sure of that?

No in cabin heat is a symptom of severe overheating, regardless of the cause of the overheating. (For example: Blown headgasket, blown water pump, busted water pump belt, etc...).

I'm not saying it's NOT the t-stat, but there are plenty of variables to consider when dealing with acute overheating.

No report of oil in coolant, no report of sweet smell from exhaust, no report of hearing a thwhack from a belt going out, it is that time of year - for whatever reason thermostats tend to go south in the fall. If it were 'acute' then he'd likely also have mentioned the burst of steam coming from under the hood when the radiator cap popped - which it sounds like it never got that bad.

I am making the assumption that there was coolant in the system - if it had all leaked out somewhere else, I'm assuming he would have mentioned that the system was empty when he looked in the radiator after it had cooled back down.

So, yes, I'm making the assumption that the person asking the question has at least some knowledge of vehicles - that they require coolant.

On a 91-92:

Very easy to get at the t-stat, without losing much coolant at all.

No jiggle valve issue as the t-stat does not sit "sideways" as on a 93-97.

There *is* an o-ring issue: Make sure you get the o-ring that sits on top of the t-stat, and install it carefully.

You're right of course - I didn't check the year. Both engines in North American trucks are fairly easy to get to the thermostat.
 
Hmm... wouldn't no heat in the cabin also be a sign of,.. Air in coolant system,.. stuck or broken temp diverter door... (or whatever they call it in the Toyota)... the temp knob becoming disconnected... I can't see it being only a sign of "severe overheating".

Why is it always worst-case scenario? Especially when we don't have clarification/complete description of the issue?

Nonsensical.
 
Hmm... wouldn't no heat in the cabin also be a sign of,.. Air in coolant system,.. stuck or broken temp diverter door... (or whatever they call it in the Toyota)... the temp knob becoming disconnected... I can't see it being only a sign of "severe overheating".

Why is it always worst-case scenario? Especially when we don't have clarification/complete description of the issue?

Nonsensical.

See the following quote:

I took a look at my temp gauge and it was in the red.

Engine temp's in the red IS worst case scenario in my book. Even my wife knows to shut 'er down IMMEDIATELY in such a situation. Do not restart; do nothing till I can give it a thorough once over.

I do agree that we need to hear back from the OP soon...
 
On a 91-92: There *is* an o-ring issue: Make sure you get the o-ring that sits on top of the t-stat, and install it carefully.

Yes I agree as the thermostats on these rigs rarely fail. The majority of problems I have seen are O-rings that are not seated, or have deteriorated or flattened over time and need to be replaced. If that o-ring does not seal, the system it is basically in bypass as the thermostats are slotted and your rig may never get up to prper temp to warm up. I would recommend replacing the two parts as a pair if you are going in there, but the stat rarely fails.

o-ring is the main culprit for the no heat issues out there....Not sure about his overheating, I would guess low coolant if he was running hot and no heat...
 
Low coolant. But after 12 posts, I think we need more input/info from the OP??

DougM
 
You sound amazingly calm for someone who just ran their engine temp's into the red. You'll be very lucky if all you need at this point is a new t-stat. (Plus that's not likely the issue.)

So what did you do? Pull over immediately? Pop the hood and check the coolant level? Listen for gurgling/boiling noises? Check all belts and hoses? Look for leaks? Or...?

No since in getting worked up over it whats done is done. I stopped to take a look under the hood. None of the above noises where heard. Belts and hoses are intact and no steam. It a 20 year old truck w/ 340k on the clock it has some issues. But I am pretty sure this issue is the thermostat. thanks for the help
 
Yes. I'm 99% sure your thermostat failed. Get an OEM one - even if you have to wait a day or two for it to come in. The parts store thermostats are junk by comparison.

It is a relatively easy job - but gets more involved when you start looking at the WYIT (While you're in there) aspects of it. With the coolant out - its probably a good time to replace all the rubber coolant hoses. Since you're replacing hoses, may as well do belts, right?

Oh, and you wouldn't want to do all of this and leave any sediment or old coolant in the system - so a multiple flush is in order. Be sure to disconnect and flush both front and rear heater cores from the firewall - and get the soft lines up underneath.

Now that you have a pristine clean system, you wouldn't want to put just any coolant in so you'll want to $28/gallon Toyota special coolant - two gallons of it. Oh, and distilled water to mix with it.

But, yes, it sounds like your thermostat failed. I'm assuming the system was full of coolant before it failed - if not, it could be very bad. Changing just the thermostat isn't hard - but you will likely drop most of your coolant to do it. Be sure to orient the jiggle valve properly.

Were you boiling water and steam out of the radiator cap? If not, I wouldn't worry about it - if the engine is hot enough to do damage and had coolant in it, the radiator cap would be screaming like a kettle in a bonfire.

IMHO YMMV I'm not a mechanic.

Thanks thats what I was thinking. It did not get hot enough to boil over or any other visible signs were present. No hot air and temp gauge went up. When I looked under the hood it was hotter than normal but other than that nothing strange. I have been planing to change all the hoses and retailed items just have not had the time to get to it yet. Thanks for the help sorry for the quick reply worked late last night and it is calling me back now. This helps a buch. Cheers
 
Keep us posted please: We haven't seen many t-stat failures in the closed position that I can recall. Hopefully that's all it is.

:beer:
 
Oh,

and hit the t-stat housing bolts with PB blaster a few times (starting a day or so ahead if possible) before removing. Quite a few folks have accidently snapped them.
 
Keep us posted please: We haven't seen many t-stat failures in the closed position that I can recall. Hopefully that's all it is.

:beer:

My 1991 stat failed that way. I forget how many years ago, but it was the original. I replace it every 4 years or so now.
 
You sound amazingly calm for someone who just ran their engine temp's into the red. You'll be very lucky if all you need at this point is a new t-stat. (Plus that's not likely the issue.)

So what did you do? Pull over immediately? Pop the hood and check the coolant level? Listen for gurgling/boiling noises? Check all belts and hoses? Look for leaks? Or...?

Well crap. Now I'm the one who get's to hope it's just the T-stat.

Driving in town after about 10 miles on the freeway, ~24* ambient temp.(!), started to overheat. Shut 'er down *really* quick; never lost heat in the cabin, gauge never made it into to the red. Belts & hoses fine, no leaks, coolant in both rad. and overflow was full but *was* boiling into/out of the overflow. After cooldown, radiator full and still some coolant in the overflow. Haven't re-started it since; got a ride home on a flat-bed and will check it out in the next couple days.

Curtis

Updates here (added 1-11-2010): https://forum.ih8mud.com/80-series-tech/350260-3fe-t-stat-failed-closed-position.html
 
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Well ****. Now I'm the one who get's to hope it's just the T-stat.

Driving in town after about 10 miles on the freeway, ~24* ambient temp.(!), started to overheat. Shut 'er down *really* quick; never lost heat in the cabin, gauge never made it into to the red. Belts & hoses fine, no leaks, coolant in both rad. and overflow was full but *was* boiling into/out of the overflow. After cooldown, radiator full and still some coolant in the overflow. Haven't re-started it since; got a ride home on a flat-bed and will check it out in the next couple days.

Curtis

Have you changed coolant recently? May be a bubble in the system.
 

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