I have a 97 chevy blazer 4.3, 4 wheel drive i had an issue where my trucks temp gage startex to rise and spiking out at 260 i would immediately pull over shut off and.give it a few to.cool then start again .. But then i noticed it would spike and i pull over and put in park and hit gas a few times and.it would.drop below the half mark and i had no heat ... So ok i replaced the thermostat, still no heat, replaced the resister, nothing, replaced the blower motor and boom i got heat but now after driving a few minutes with heat on it will still spike at the 260 mark i would pull over pop in neutral hit the gas a few times and it comes down to below half put in drive and drive a few minutes like.maybe 10 if that and boom back.up to 260 im at a loss i dont know what could be the problem, theres no leaks all hoses are hot so nothing plugged clutch fan working any ideas would be appreciated.

 

Water pump. Mine did that before I replaced the water pump. There's an impeller inside thats probably worn down so that it no longer pushes coolant efficiently enough to maintain engine temp. Do yourself a favor and get an AC Delco pump. I've been through 3 of the store brand models (Carquest at Advance Auto Parts)in the last 6 months. It gets expensive replacing coolant at that rate. And be sure to use the included gaskets, use some high temp RTV, clean the mating surfaces thoroughly (I used a brass brush on a drill. Worked perfectly). And torque the bolts to the proper specs. It was 33 foot pounds on mine, but I have an 02. I'm sure it's the same for your 97, but double check to be sure. Hope this cures you.
I would also change the oil while you're at it, since those overheating cycles probably baked it. Also, you will need a 36mm wrench to remove the fan. I rented one from Auto Zone for $20. A quick YouTube search should yield several ways to remove it.
Let us know how it turns out.

 

i replaced the water pump and still same problem but this time i hear a rattling kinda knocking in my dash when that stops the temp drops below the half mark no steam, no smell of antifreeze, truck runs fine . no clue why its doing this.
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