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Discussion Starter · #1 ·
How do I know if my water temp sensors are bad or going bad, I had my cooling system flushed replace the water from electric to stock, replace the stat twice an did the hot water test on the stat to see if it working, bleed the system of air, and the fans are working fine. An it keep going past the half way spot an up the the white line before the h, so now I think it the sensors. An input on how I would if they bad please help thanks.
 

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When do the fans come on? My primary start's at a tic above the 1/2 mark on my gauge, I have never seen the secondary go on since I replaced the primary, ...at that time the secondary used to kick in at the last white line before the the red...scared the crap out of me in downtown gridlock, but it cooled down and didn't over heat. Your primary fan might be out or on it's way out, as in spining...but not fast enough. Does it run hot with the A/C on?
 

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Are you running a stock PCM program?

The gauge in the instrument cluster reads from the sender in the RH cylinder head. The sensor in the water pump is for the PCM only.

Do you have a volt-ohm meter? I seem to remember there being a chart in the service manual for resistance to indicate what temperature the sender is showing. I'll have to see what I can find.
 

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An it keep going past the half way spot an up the the white line before the h, so now I think it the sensors. An input on how I would if they bad please help thanks.
Half way is not hot. With stock programming, the PCM does not command the fan(s) on until 225 F primary and 232 F secondary. That's well past halfway on the gauge. Most GM temp gauges run from 100 to 260 F and have 210 F at the halfway point, they are not linear.

Here's a chart that's good for most GM sensors:

 

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Discussion Starter · #5 ·
Ok here's the problem I'm having now I replace the stat with a brand new one, an put back on my stock water pump, I bleed the system the best way I could, but I still keep getting little bubbles in the in my coolant tank when I open the throttle up, I also notice when I turn the heat on high when I'm driving the car gets cooler. Can any tell me what's going on?
 

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When do the fans come on? My primary start's at a tic above the 1/2 mark on my gauge, I have never seen the secondary go on since I replaced the primary, ...at that time the secondary used to kick in at the last white line before the the red...scared the crap out of me in downtown gridlock, but it cooled down and didn't over heat. Your primary fan might be out or on it's way out, as in spining...but not fast enough. Does it run hot with the A/C on?
Interesting you should mention a "not completely dead" fan. I thought that was at least one thing that either worked - or not. I'm getting peculiar overheating symptoms that are different than anything I ever recall in 15 years. At 75mph it sets there at 1/4 mark all day no matter how hot out. In traffic at 30-50 it now gets up to 3/4 without trouble, it never did that years before - ever. I was going to swap out the thermostat just because. And I vaguely recall hearing 20-30 years ago that antifreeze can get "weak" after too many years, so I figured even if that's just an old wive's tale that I'd finally just do a flush - it's been 6-7 years at least.

This fan slowly dying issue is interesting though.

BTW, previously swapped a known good cap from my Cadillac, this is the Impala with just a 3000Edge, good tune, headers, fresh air and catbacks.
 

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but I still keep getting little bubbles in the in my coolant tank when I open the throttle up, I also notice when I turn the heat on high when I'm driving the car gets cooler. Can any tell me what's going on?
Bubbles in the coolant when you rev it up are NOT a GOOD thing.....turning the heater on lowers the temp because you are disipating (sp) some of the heat. It can help in a jam if you are borderline overheating.
 

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At 75mph it sets there at 1/4 mark all day no matter how hot out. In traffic at 30-50 it now gets up to 3/4 without trouble, it never did that years before - ever.
This fan slowly dying issue is interesting though.

BTW, previously swapped a known good cap from my Cadillac, this is the Impala with just a 3000Edge, good tune, headers, fresh air and catbacks.
Mine stay's right about the 1/4 mark as long as I'm doing 45 or better, which IIRC is when the fans are programmed out...I.E. not needed. Stop & go in 115 degree's it will slowly climb to almost 1/2 if I'm stopped long enough even with the A/C on. I did notice when my pri. fan was out that keeping RPM's up around 1800 helped cool things down a bit, better flow from the WP is all I can figure.
 

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If coolant is boiling in the tank before your gauge is buried in the red, your system is losing pressure somewhere. Coolant cap is the most likely cause.
 
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