Bad Thermostat?

[villevol666]

So I was driving home yesterday from my grandparents house, about an hour drive, and in the last mile or so, my heater stopped blowing hot air and when I parked, there was steam spewing from the coolant tanks overflow tube.

Is this the sign of a bad Thermostat? I've already replaced the otterstat a few months ago, so I know the fans are running when they should, but because of where the otterstat is located in the system, if the thermostat is frozen closed, hot water would never pass by the otterstat to activate it, correct?

Thanks,
Brandon

[DMC5180]

Was your last mile of driving at slow in town stop n go?


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[DMC5180]

Was your last mile of driving at slow in town stop n go?


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Did you observe a higher than normal water temp?


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[villevol666]

Last mile was still on the freeway. Unfortunately, I'm not sure if the temperature because the gauge stopped working 2 weeks ago.

[AugustneverEnds]

Notice any coolant drips anywhere? You may have a small leak the allowed enough air in to airlock the cooling system. Having a pressure tester is very useful on occasions like these, Autozone will loan you one if you don't have access to one

[Rich]

So I was driving home yesterday from my grandparents house, about an hour drive, and in the last mile or so, my heater stopped blowing hot air and when I parked, there was steam spewing from the coolant tanks overflow tube.

Is this the sign of a bad Thermostat? I've already replaced the otterstat a few months ago, so I know the fans are running when they should, but because of where the otterstat is located in the system, if the thermostat is frozen closed, hot water would never pass by the otterstat to activate it, correct?

Thanks,
Brandon

Maybe, but more likely this is a sign of either low coolant level (leak), a poorly-bled cooling system or the rad fans failing. The first two issues would be a problem at any speed, the last one would be a problem around town except in hot weather - which we do not have in SF this weekend. Sounds like the heater stopped working after the freeway segment of your drive.

Refill the system, making sure it is bled correctly. Then make sure the otterstat is behaving correctly (harder to do if the temp gauge isn't working, though) during some around-town testing or idling for 10-15min. Also make sure your otterstat pipe tee is facing downward (otterstat needs to be under the pipe, not above it).

Have you noticed any signs of coolant leakage recently? Nick's pressure test is a good idea.

[DMC5180]

Last mile was still on the freeway. Unfortunately, I'm not sure if the temperature because the gauge stopped working 2 weeks ago.

Hate to say it, but there is a lesson to be learned here. You must have some kind of temp indication whether a gauge or warning light. Deloreans don’t have warning lights, so you must have a functional gauge.

My guess is your cooling fans are not functioning like you think.

Unplug the wires at the otterstat add jumper them to gather, turn the key to run, they should turn ON. If they don’t you’ll need to troubleshoot.




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[villevol666]

Fans are new. Replaced 5 months ago.

[DMC5180]

Fans are new. Replaced 5 months ago.

Doesn’t mean they are turning ON when needed though. What setup do you have in place of the blue fan fail module?


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[villevol666]

Not sure I have anything in place of the blue fail module. Having said that, if the fans work, the otterstat works, the relay works and the fans come on when I jump the otterstat, how could it be fan related?

[dmcnc]

What's your coolant level? Have you bleed the air out?

[Bitsyncmaster]

If the thermostat froze closed your otterstat would not get hot and the fans would not turn on. But since no coolant is flowing through the radiator, it would not help to have the fans run anyway.

Your first thing to do it get your temp gauge working. The temp gauge works even if the thermostat is frozen shut. There is coolant flowing in the engine. Try unplugging and plugging in the bulkhead connectors to see if that fixes your temp gauge.

[villevol666]

Which bulk head is it specifically?

Edit: nevermind, I cleaned them all with wd40 and a wire brush, I'm back in business.

Checking to see if the fans turn on

[villevol666]

Fan is not turning on. Coolant pipe from the front of the car, i.e pipe with the otterstat is cool too the touch...

Water pump?

Edit: antifreeze in overflow tank also cold.

[DMC5180]

Not sure I have anything in place of the blue fail module. Having said that, if the fans work, the otterstat works, the relay works and the fans come on when I jump the otterstat, how could it be fan related?

At this point, you’re just trying to verify that they do work and that they come on when the otterstat turns them on.

Assuming you don’t have the blue fan fail module, there should be something else plugged into the blue socket. A Y- jumper or Fused Y-jumper at minimum.


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[DMC5180]

Fan is not turning on. Coolant pipe from the front of the car, i.e pipe with the otterstat is cool too the touch...

Water pump?

Edit: antifreeze in overflow tank also cold.

Does that mean your temp gauge is working again?


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[villevol666]

Yes, temp gauge is working again. Coolant in pipe from radiator never heats up, I'm going to swap the thermostat now.

[villevol666]

Thanks for everyone's help, it was the thermostat.

[Rich]

Thanks for everyone's help, it was the thermostat.

Way to go. That was a quick resolution by you and the forum team.

Thanks for the closure report. Glad you'll be back on the road now.

[David T]

Rare for a thermostat to fail but possible. Make sure the new one has a "jiggle pin" and if not at least drill a 1/16" hole in it to pass air so you can bleed the system of air. Watch your coolant level, if you have a leak you can overheat. Bleed the system, at the water pump and the small hose top right side of the radiator. Make sure the header bottle is 1/2 full cold with 50/50 anti-freeze and soft water. Make sure your fans come on and do the relay upgrade and fan fail bypass. If you still have the original radiator with the plastic tanks you should replace it. Ditto for the plastic header bottle.

[villevol666]

The old thermostat was a corroded mess, I can't believe it was working at all.

[DMC5180]

The old thermostat was a corroded mess, I can't believe it was working at all.

Glad you got it sorted out. Follow the bleeding steps David T mentioned.

Can you post a photo of the old thermostat? The corrosion at the thermostat seems highly unusual, however, it could be an indicator of other problems to come.


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[David T]

If the old thermostat was a "corroded mess" the entire cooling system should be flushed out several times. If the thermostat was corroded you can only guess what else and how bad the system is.