Weird Cooling Issue... Sticky Thermostat?

Hey

So, background is 89 GT with 100k original miles. Stock. Have been driving it for 2 years without the temp gauge (an aftermarket / accurate temp gauge) going above 190* even in august.

Driving to work the other morning and it climbs to over 210, so I pull over and check it out.

Radiator hose and radiator are cold. So I think, ok stuck thermo.

Let it cool down, turn around and drive home, starts to climb again then all of a sudden boom temp drops back to rock solid. So ya, thermostat, I figure I'll replace it anyway.

Replaced it with a motorcraft thermo, same issue. Made sure the coolant was full, let engine warm up with cap off to keep filling coolant... engine climbs over 210 again. Then all of a sudden, boom, comes down, take it for a drive and it's rock solid again.

What else should I be looking for? I'm going to try again tomorrow morning and see if it happens... but has anyone experienced this?

Thanks.
 
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I'm mister limited on this experience since my car is a shell just beginning rebuild, but...

Logically, first thing would be the thermostat. You tried that.

Second, air in the system. Bleed it out.

Third (to me) could be the water pump itself.

Let's get some more intelligent help on here, rather than depending on my haphazard guessing. @Boosted92LX @stykthyn @TOOLOW91 @hoopty5.0 @jrichker

Those guys are bound to know.
 
Just went through this and put a motorcraft in my car that was drilled at 12 and 6 for air pocket relief and extra flow when it's closed .

Im guessing it has a stock rad and fan ? Is the clutch worn on the fan that's also a possibility .

Take it for another ride and report back .


Sent from my iPhone using my fingers while my auto correct makes me seem illiterate
 
ok. is this a stock or afterrmarket gauge?

Things to check
  • Is the thermostat tested in boiling water to see if it is operational
  • lower hose not collapsing
  • Sending unit on the gauge
  • air pocket in the system
  • bad ground for the gauge
 
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I have seen the temp gauge go up and then quickly drop back down. It is usually due to low coolant level or air in the cooling system. The sudden drop is because the thermostat opened and coolant began circulating through the radiator.
 
Late to the party, but these guys have covered it. I'll throw in also that a thermostat installed backwards will cause problems as well.

Edit:
Oh yeah, the lower rad hose has a spring it (some do anyway) to prevent collapse. If that spring rusts out and the hose collapses, the water pump can't pull water and funny things happen. Might check that as well.
 
Replaced it with a motorcraft thermo, same issue. Made sure the coolant was full, let engine warm up with cap off to keep filling coolant... engine climbs over 210 again. Then all of a sudden, boom, comes down, take it for a drive and it's rock solid again.

What else should I be looking for? I'm going to try again tomorrow morning and see if it happens... but has anyone experienced this?

What exactly is the problem?