Coolant temp runs hot ALL THE SUDDEN!

[micruz60]

If I remember it’s fiber.

That's good news. I recall doing a t-stat swap along with cooling system maintenance, and the circular gasket was basically heat-glued to the upper half of the housing and it had disintegrated such that there was rubber scum floating at the radiator cap. Several coolant flushes later (and a fiber gasket) all's well.

 

[Pighead]

Maybe running the engine without a thermostat for a few days after changing coolant would purge the air much faster. I don’t know though. Never tried it.

Would one not re-introduce air into the cooling system when re-installing the thermostat?

 

[LandoNick]

Would one not re-introduce air into the cooling system when re-installing the thermostat?

I guess anytime you open the system you risk that?

 

[LandoNick]

Would air in the system gradually raise the temp sensor or would it spike?

 

[ToyotaMatt]

Would air in the system gradually raise the temp sensor or would it spike?

this topic has not been discussed yet , you have replaced everything in your system in recent time window of or before it's expected life cycle would be over , so lets

conclude for a moment this is your issue because its over 30 years old and original ?


u can FSM step by step it , or take the path of both a guarantee and least resistance ........

- and to be krystal klear if your quickie-jack flash fast , and your RED cap is on tight , and land Cruiser cool engine first thing in morning ( T-STAT Closed up tite )

NO coolant draining is necessary........

Genuine YAZAKI OEM Gage Assy, Water Temperature Sender Sensor 2/76 - 92 FJ40 FJ55 FJ60 FJ70 FJ80 FJ62 / 2F / 3F carb / 3F-E / 3FE Updated Marine Grade Alloy Tin Plated Repair Connector KIT & Special positive grip locking detent ball terminal - Vi

Genuine YAZAKI Japan spec. parts for Cluster meter Gage Assy, Water Temperature sensor / sending unit Fits 2/76 - 92...

vintageteqparts.com

 

[OSS]

The 2F temperature sender is oriented vertically which traps an air pocket around it. If there’s any frothing going on inside the cooling system from the water pump chewing up bubbles, those micro bubbles will migrate everywhere in the cooling system and coalesce in trapped pockets. The space around the temperature sender is one of those pockets.
When enough air finds its way around the gap surrounding the sensor, as new micro bubbles join in, the sensor ends up being completely out of the coolant. It’s not touching coolant at all. It’s dry.
At that point the sensor is then measuring the temperature through its threads screwed into the adapter fitting screwed into the head. It’s measuring the actual cast iron temperature, not the temperature of the coolant which is always cooler.

The 3F engine fixed this problem by having the temperature sender installed sideways in the thermostat housing. It doesn’t trap air and measures the same temperature the thermostat gets.

If the thermostat housing cap is removed on a full system, only an air bubble will form on the top half of the housing when it’s sealed back up. This area will purge directly to the radiator even in a cold engine, so none of that air should get sucked back into the water pump (I think)

 

[LandoNick]

Ok I think OSS was right I think I still had some bubbles in the system. Free way driving with the heat on and rear heat on. The temp stayed rock steady in the middle. so Hopefully that was the end of that.