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Discussion Starter · #1 ·
I went for a ride in my Chevelle, watching my gauges as it was warming up just glanced at the water temp, it was rising to 200, 210, 220, 230, OH MY God, then all of a sudden the gauge flew down to 180 as usual. It almost sounds like the thermostat was stuck then flew open. Whats your thoughts?

Dave
 

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I had this very thing happen years ago. It was the new thermostat in my case. Replaced it and everything was fine. In fact, visually, it looked fine too.
 

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Did you recently drain the coolant system and not burp it afterward? I had the same symptoms last year because I didn't burp. (The system, that is!)
 

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I used to have that happen with the old motor.

The motor never acted hot when it happened and the temp always dropped very quickly back to normal.

That was with a hi flo Mr G thermostat mounted in the head (interesting that PCB mentioned that location too) and a mechanical gauge.

Since rebuilding the motor and moving the sender to the intake I haven't had the problem re-occur.
 

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Discussion Starter · #6 ·
My sending unit is in the intake, I replaced the thermostat, hopefully thats got it. I actually started to pull over I thought I would of been walking for sure.

Dave
 

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I lived in Saudi Arabia and drove a '79 Mazda 4-banger beater. I'd watch the aftermarket temp gauge go up,up,up until it just dropped rapidly to around 180ish after a few minutes on the freeway. Did it all the time-- winter and summer and in between. No air in the system; checked that. I just chalked it up to characteristic of the thermostat.

My $0.02
 

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On my 66 stock 396/325 with 180 tstat and mech gauge in the intake, when I start it up, it always slowly rises to 185-190 then drops fast to 160, then slowly rises to 185, then drops to 170 then rises and settles at around 185. Never gets too hot so I am thinking its OK.
 
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