99 Blazer-- Water Temp Instantly raises in dead traffic, fine on the free way-- Is it the fan clutch?

99 Blazer, A/C, 4x4..161k
Cooling System Background:
I had the dealer flush the dexcool about 5000 miles ago. The dealer said there was some funky stuff in the radiator, and that I had made a
good call getting it flushed. Sometimes I hear gurgling from the heater core. No wet passenger floor surprises so far, and the heat still works.
The Symptoms:
Driving through low-speed or no speed, city traffic, the water temperature quickly gets into the 230-235 degree range. When I get to highway speeds, the vehicle instantly goes back to normal operating temperature of about 190 degrees.
In my past S10 Blazers, an 86, and a 93, when things got hot, the fan clutch would firm up and you'd hear the familiar loud fan whooshing sound.
Not-so-scientific testing:
My roommate has a 97 blazer. I got both vehicles up to operating temperature... and mine beyond that to 230 degrees driving around the block a few times. His fan has a bit more resistance than than mine does when trying to turn the fan.
I'm fairly convinced the fan clutch is most likely the problem. What other elements in the cooling system could cause a consistent behavior like this?
Regards,
Lane Jennison
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When the engine is at operating temp the usual way to test the clutch is to spin by hand, should turn maybe 2 blades at most. Could be air in the cooling system also from the flush, although this would have showed up right away. Look in the rad when cold may have to drain some coolant down, look at the core tubes and see if the are clogged with the coolant contamination residue.

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Thermostat stuck open, Has it been changed lately ?
Larry
Lane Jennison wrote:

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Most likely not.. I've only had the vehicle since 153k.
If its stuck open, wouldn't that cause it to run cooler instead of hotter?
Larry wrote:

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"Lane Jennison" wrote:

It can run hotter with it stuck open but usually on highway not around town. This is a clutch fan cooling problem and nothing more. Year ago I had a old Jeep truck that did simularly and I replaced clutch fan and problem went away and never came back.
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SnoMan wrote:

Right On. Thanks for the input. I will repair it tomorrow and follow-up.
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"noones" wrote: > Thermostat stuck open, Has it been changed lately ? > > Larry > > > Lane Jennison wrote: > > 99 Blazer, A/C, 4x4..161k > > > > > > Cooling System Background: > > > > I had the dealer flush the dexcool about 5000 miles ago. > The dealer > > said there was some funky stuff in the radiator, and that I > had made a > > good call getting it flushed. Sometimes I hear gurgling > from the heater > > core. No wet passenger floor surprises so far, and the heat > still works. > > > > The Symptoms: > > > > Driving through low-speed or no speed, city traffic, the > water > > temperature quickly gets into the 230-235 degree range. > When I get to > > highway speeds, the vehicle instantly goes back to normal > operating > > temperature of about 190 degrees. > > > > In my past S10 Blazers, an 86, and a 93, when things got > hot, the fan > > clutch would firm up and you'd hear the familiar loud fan > whooshing sound. > > > > Not-so-scientific testing: > > > > My roommate has a 97 blazer. I got both vehicles up to > operating > > temperature... and mine beyond that to 230 degrees driving > around the > > block a few times. His fan has a bit more resistance than > than mine > > does when trying to turn the fan. > > > > I'm fairly convinced the fan clutch is most likely the > problem. What > > other elements in the cooling system could cause a > consistent behavior > > like this? > > > > Regards, > > > > Lane Jennison
My nickel is on a defective clutch fan hub. Classic signs of failure.
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My vote is on the fan clutch also.

http://www.autoforumz.com/Chevrolet-99-Blazer-Water-Temp-Instantly-raises-de ad-traffic-fine-ftopict120749.html
http://www.autoforumz.com/eform.php?pX7140
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