Coolant temp runs hot ALL THE SUDDEN! (1 Viewer)

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In the last 2 days during freeway driving the coolant temp on the gauge has been creeping up. Typically it's dead center on the gauge. About 3-4 months ago replaced the temp. sensor and the wire with a new boot insulator. Coolant was still reading in the middle . Now I know the temp gauge is garbage and doesn't work great. The last couple of days I have checked the temp with a IR thermometer at the thermostat it was 192, Top radiator hose 190, at the temp sensor it was like 230. Not sure if its supposed to be that high. It does not get hotter then normal around town only free way.
 

cwwfj60

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Sounds like you are cool enough based on IR….230 is high but about what I get on IR depending on brand and quality.

Where does the gauge read? 3/4? Touching the red? Mine usually read above half here in Texas

Belts tight? I had a belt that would slip just enough to get warm, but not overheat…failing smog pump too….

Lastly, have you had the system open recently? Air bubble would cause this. Turn the heater on for a bit and burp the system maybe.
 

micruz60

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What Cody wrote ^^ is what I thought as well, air bubble; run it at operating temps with the heater on, check coolant overflow bottle for drawdown and refill. Is the radiator cap OEM and still working properly?
 

OSS

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The back of the head is the hottest part of the engine. My 2F with a completely overhauled cylinder head and new Toyota head gasket, new 190°F thermostat, new upper thermostat housing, new radiator, new calibrated Toyota temperature sender and a few year old water pump ran approximately 30° hotter at the back of the head at the sender location than at the thermostat. 220°F rear, 192°F front.
It wasn’t a matter of purging air either.

It’s a bit unsettling to see it - but that’s how it runs normally (for 35 years).

The water circulation inside the head isn’t even. The front runs cooler than the back.
 
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Sounds like you are cool enough based on IR….230 is high but about what I get on IR depending on brand and quality.

Where does the gauge read? 3/4? Touching the red? Mine usually read above half here in Texas

Belts tight? I had a belt that would slip just enough to get warm, but not overheat…failing smog pump too….

Lastly, have you had the system open recently? Air bubble would cause this. Turn the heater on for a bit and burp the system maybe.
yeah I thought that was a pretty Normal temp..

will get up to 3/4 after a freeway run.

belts are tight but could loosen when warm. Smog pump is deleted

I did recently replace a broken BVSB violet one.

so turn on the heater squeeze the upper hose? I did replace the coolant with a funnel that connects to the radiator cap.

why only when on the freeway. I also have a H55 is it possible that the water pump would not flow enough water at that RPM?
 
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What Cody wrote ^^ is what I thought as well, air bubble; run it at operating temps with the heater on, check coolant overflow bottle for drawdown and refill. Is the radiator cap OEM and still working properly?
Cap is OEM new. Also new water pump, new radiator, thermostat hoses clamps. all couple years age
 
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The back of the head is the hottest part of the engine. My 2F with a completely overhauled cylinder head and new Toyota head gasket, new 190°F thermostat, new upper thermostat housing, new radiator, new calibrated Toyota temperature sender and a few year old water pump ran approximately 30° hotter at the back of the head at the sender location than at the thermostat. 220°F rear, 192°F front.
It wasn’t a matter of purging air either.

It’s a bit unsettling to see it - but that’s how it runs normally (for 35 years).

The water circulation inside the head isn’t even. The front runs cooler than the back.
I just don't get the random timing and the only Free way. then is cools dow after I get to residential roads
 

micruz60

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Good to be concerned about it, but maybe not a major issue, freeway speeds, and free flowing air thru radiator would rule out fan clutch; is the radiator suspect- no clogged fins ?
 
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I ran my truck from Florida to Montana loaded at 65-75mph and it got up to about 197-198 at the thermostat on the hottest part of the trip, but normally ran about 192-194. My set up is different than yours and I have a digital read out from the coolant drain on the back of the block. I ran it hard on the highway for about a week every day and I never had issues with it running at those temps.
 
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Good to be concerned about it, but maybe not a major issue, freeway speeds, and free flowing air thru radiator would rule out fan clutch; is the radiator suspect- no clogged fins ?
Yeah I thought about the fan clutch did the “magazine “ test and it didn’t stop. There was some good resistance. I also thin it would overheat in town. Newish radiator a couple years old.
 

OSS

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If the cooling system is opened up to replace coolant, air will get in the system and the temperature gauge will definitely show hot (even on the freeway) for a few weeks until all the air eventually purges out. It can take a long time.
 

cwwfj60

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so turn on the heater squeeze the upper hose? I did replace the coolant with a funnel that connects to the radiator cap.

Ya, but reinstall the funnel and fill it 3/4, even park at an incline if you can. The area around the temp sender seems to be the most likely to accumulate a pocket of air…which spikes the gauge.

That being said, you may be looking at normal running conditions and wonky 60 temp gauges.
 
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I ran my truck from Florida to Montana loaded at 65-75mph and it got up to about 197-198 at the thermostat on the hottest part of the trip, but normally ran about 192-194. My set up is different than yours and I have a digital read out from the coolant drain on the back of the block. I ran it hard on the highway for about a week every day and I never had issues with it running at those temps.
The the random of it all is weird to me.
 
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If the cooling system is opened up to replace coolant, air will get in the system and the temperature gauge will definitely show hot (even on the freeway) for a few weeks until all the air eventually purges out. It can take a long time.
What is the best purge practice?
 

OSS

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I think natural purging takes a long time because at first start up of a cold engine that has air in it, the coolant is recirculating inside the engine and not flowing into the radiator.

The radiator is a natural air separator, keeping air on top and coolant below, but when the engine is warming up, any air in the system gets sucked directly back into the spinning water pump which then whips the big bubbles into microscopic frothy bubbles which then circulate all throughout the cooling system to get trapped & coalesce in pockets around the head.

It’s a vicious cycle, but eventually, given enough time while driving, the bubbles end up in the radiator which separates them out.

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.
 

micruz60

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Yeah I thought about the fan clutch did the “magazine “ test and it didn’t stop. There was some good resistance. I also thin it would overheat in town. Newish radiator a couple years old.
Yes, fan clutch is more of a stop-and-go city driving cooling assist.
Good to be cautious about the concern, but it may just need some time to work out the air bubble at the sender?
Oh, jeez, just thought of this, the circular gasket that sits atop the thermostat- really shouldn't be a factor, but is it a fiber one or a rubber one?
 

micruz60

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I think natural purging takes a long time because at first start up of a cold engine that has air in it, the coolant is recirculating inside the engine and not flowing into the radiator.

The radiator is a natural air separator, keeping air on top and coolant below, but when the engine is warming up, any air in the system gets sucked directly back into the spinning water pump which then whips the big bubbles into microscopic frothy bubbles which then circulate all throughout the cooling system to get trapped & coalesce in pockets around the head.

It’s a vicious cycle, but eventually, given enough time while driving, the bubbles end up in the radiator which separates them out.

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.
Cavitation of that air is not good, but by doing the burp, doesn't that essentially eliminate the air in the system, and then closing up the top of the radiator (overflowing when burped), then maintaining the overflow bottle such that no air gets drawn in solve this?
 

OSS

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Yes but a first start up on a cold engine, the thermostat is closed so any air in the system that burps into the thermostat housing get sucked straight into the spinning water pump and whipped into tiny bubbles. Only when the thermostat opens is “burping” effective.

In the end it all works itself out. It just takes longer than we want it to.
 
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Yes, fan clutch is more of a stop-and-go city driving cooling assist.
Good to be cautious about the concern, but it may just need some time to work out the air bubble at the sender?
Oh, jeez, just thought of this, the circular gasket that sits atop the thermostat- really shouldn't be a factor, but is it a fiber one or a rubber one?
If I remember it’s fiber.
 

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